kvm/mmu/tdp_mmu.c

// SPDX-License-Identifier: GPL-2.0

#include "mmu.h"
#include "mmu_internal.h"
#include "mmutrace.h"
#include "tdp_iter.h"
#include "tdp_mmu.h"
#include "spte.h"

#include <asm/cmpxchg.h>
#include <trace/events/kvm.h>

static bool __read_mostly tdp_mmu_enabled = true;
module_param_named(tdp_mmu, tdp_mmu_enabled, bool, 0644);

/* Initializes the TDP MMU for the VM, if enabled. */
int kvm_mmu_init_tdp_mmu(struct kvm *kvm)
{
	struct workqueue_struct *wq;

	if (!tdp_enabled || !READ_ONCE(tdp_mmu_enabled))
		return 0;

	wq = alloc_workqueue("kvm", WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE, 0);
	if (!wq)
		return -ENOMEM;

	/* This should not be changed for the lifetime of the VM. */
	kvm->arch.tdp_mmu_enabled = true;
	INIT_LIST_HEAD(&kvm->arch.tdp_mmu_roots);
	spin_lock_init(&kvm->arch.tdp_mmu_pages_lock);
	INIT_LIST_HEAD(&kvm->arch.tdp_mmu_pages);
	kvm->arch.tdp_mmu_zap_wq = wq;
	return 1;
}

/* Arbitrarily returns true so that this may be used in if statements. */
static __always_inline bool kvm_lockdep_assert_mmu_lock_held(struct kvm *kvm,
							     bool shared)
{
	if (shared)
		lockdep_assert_held_read(&kvm->mmu_lock);
	else
		lockdep_assert_held_write(&kvm->mmu_lock);

	return true;
}

void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm)
{
	if (!kvm->arch.tdp_mmu_enabled)
		return;

	flush_workqueue(kvm->arch.tdp_mmu_zap_wq);
	destroy_workqueue(kvm->arch.tdp_mmu_zap_wq);

	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_pages));
	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_roots));

	/*
	 * Ensure that all the outstanding RCU callbacks to free shadow pages
	 * can run before the VM is torn down.  Work items on tdp_mmu_zap_wq
	 * can call kvm_tdp_mmu_put_root and create new callbacks.
	 */
	rcu_barrier();
}

static void tdp_mmu_free_sp(struct kvm_mmu_page *sp)
{
	free_page((unsigned long)sp->spt);
	kmem_cache_free(mmu_page_header_cache, sp);
}

/*
 * This is called through call_rcu in order to free TDP page table memory
 * safely with respect to other kernel threads that may be operating on
 * the memory.
 * By only accessing TDP MMU page table memory in an RCU read critical
 * section, and freeing it after a grace period, lockless access to that
 * memory won't use it after it is freed.
 */
static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
{
	struct kvm_mmu_page *sp = container_of(head, struct kvm_mmu_page,
					       rcu_head);

	tdp_mmu_free_sp(sp);
}

static void tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
			     bool shared);

static void tdp_mmu_zap_root_work(struct work_struct *work)
{
	struct kvm_mmu_page *root = container_of(work, struct kvm_mmu_page,
						 tdp_mmu_async_work);
	struct kvm *kvm = root->tdp_mmu_async_data;

	read_lock(&kvm->mmu_lock);

	/*
	 * A TLB flush is not necessary as KVM performs a local TLB flush when
	 * allocating a new root (see kvm_mmu_load()), and when migrating vCPU
	 * to a different pCPU.  Note, the local TLB flush on reuse also
	 * invalidates any paging-structure-cache entries, i.e. TLB entries for
	 * intermediate paging structures, that may be zapped, as such entries
	 * are associated with the ASID on both VMX and SVM.
	 */
	tdp_mmu_zap_root(kvm, root, true);

	/*
	 * Drop the refcount using kvm_tdp_mmu_put_root() to test its logic for
	 * avoiding an infinite loop.  By design, the root is reachable while
	 * it's being asynchronously zapped, thus a different task can put its
	 * last reference, i.e. flowing through kvm_tdp_mmu_put_root() for an
	 * asynchronously zapped root is unavoidable.
	 */
	kvm_tdp_mmu_put_root(kvm, root, true);

	read_unlock(&kvm->mmu_lock);
}

static void tdp_mmu_schedule_zap_root(struct kvm *kvm, struct kvm_mmu_page *root)
{
	root->tdp_mmu_async_data = kvm;
	INIT_WORK(&root->tdp_mmu_async_work, tdp_mmu_zap_root_work);
	queue_work(kvm->arch.tdp_mmu_zap_wq, &root->tdp_mmu_async_work);
}

static inline bool kvm_tdp_root_mark_invalid(struct kvm_mmu_page *page)
{
	union kvm_mmu_page_role role = page->role;
	role.invalid = true;

	/* No need to use cmpxchg, only the invalid bit can change.  */
	role.word = xchg(&page->role.word, role.word);
	return role.invalid;
}

void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root,
			  bool shared)
{
	kvm_lockdep_assert_mmu_lock_held(kvm, shared);

	if (!refcount_dec_and_test(&root->tdp_mmu_root_count))
		return;

	WARN_ON(!root->tdp_mmu_page);

	/*
	 * The root now has refcount=0.  It is valid, but readers already
	 * cannot acquire a reference to it because kvm_tdp_mmu_get_root()
	 * rejects it.  This remains true for the rest of the execution
	 * of this function, because readers visit valid roots only
	 * (except for tdp_mmu_zap_root_work(), which however
	 * does not acquire any reference itself).
	 *
	 * Even though there are flows that need to visit all roots for
	 * correctness, they all take mmu_lock for write, so they cannot yet
	 * run concurrently. The same is true after kvm_tdp_root_mark_invalid,
	 * since the root still has refcount=0.
	 *
	 * However, tdp_mmu_zap_root can yield, and writers do not expect to
	 * see refcount=0 (see for example kvm_tdp_mmu_invalidate_all_roots()).
	 * So the root temporarily gets an extra reference, going to refcount=1
	 * while staying invalid.  Readers still cannot acquire any reference;
	 * but writers are now allowed to run if tdp_mmu_zap_root yields and
	 * they might take an extra reference if they themselves yield.
	 * Therefore, when the reference is given back by the worker,
	 * there is no guarantee that the refcount is still 1.  If not, whoever
	 * puts the last reference will free the page, but they will not have to
	 * zap the root because a root cannot go from invalid to valid.
	 */
	if (!kvm_tdp_root_mark_invalid(root)) {
		refcount_set(&root->tdp_mmu_root_count, 1);

		/*
		 * Zapping the root in a worker is not just "nice to have";
		 * it is required because kvm_tdp_mmu_invalidate_all_roots()
		 * skips already-invalid roots.  If kvm_tdp_mmu_put_root() did
		 * not add the root to the workqueue, kvm_tdp_mmu_zap_all_fast()
		 * might return with some roots not zapped yet.
		 */
		tdp_mmu_schedule_zap_root(kvm, root);
		return;
	}

	spin_lock(&kvm->arch.tdp_mmu_pages_lock);
	list_del_rcu(&root->link);
	spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
	call_rcu(&root->rcu_head, tdp_mmu_free_sp_rcu_callback);
}

/*
 * Returns the next root after @prev_root (or the first root if @prev_root is
 * NULL).  A reference to the returned root is acquired, and the reference to
 * @prev_root is released (the caller obviously must hold a reference to
 * @prev_root if it's non-NULL).
 *
 * If @only_valid is true, invalid roots are skipped.
 *
 * Returns NULL if the end of tdp_mmu_roots was reached.
 */
static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
					      struct kvm_mmu_page *prev_root,
					      bool shared, bool only_valid)
{
	struct kvm_mmu_page *next_root;

	rcu_read_lock();

	if (prev_root)
		next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
						  &prev_root->link,
						  typeof(*prev_root), link);
	else
		next_root = list_first_or_null_rcu(&kvm->arch.tdp_mmu_roots,
						   typeof(*next_root), link);

	while (next_root) {
		if ((!only_valid || !next_root->role.invalid) &&
		    kvm_tdp_mmu_get_root(next_root))
			break;

		next_root = list_next_or_null_rcu(&kvm->arch.tdp_mmu_roots,
				&next_root->link, typeof(*next_root), link);
	}

	rcu_read_unlock();

	if (prev_root)
		kvm_tdp_mmu_put_root(kvm, prev_root, shared);

	return next_root;
}

/*
 * Note: this iterator gets and puts references to the roots it iterates over.
 * This makes it safe to release the MMU lock and yield within the loop, but
 * if exiting the loop early, the caller must drop the reference to the most
 * recent root. (Unless keeping a live reference is desirable.)
 *
 * If shared is set, this function is operating under the MMU lock in read
 * mode. In the unlikely event that this thread must free a root, the lock
 * will be temporarily dropped and reacquired in write mode.
 */
#define __for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, _only_valid)\
	for (_root = tdp_mmu_next_root(_kvm, NULL, _shared, _only_valid);	\
	     _root;								\
	     _root = tdp_mmu_next_root(_kvm, _root, _shared, _only_valid))	\
		if (kvm_lockdep_assert_mmu_lock_held(_kvm, _shared) &&		\
		    kvm_mmu_page_as_id(_root) != _as_id) {			\
		} else

#define for_each_valid_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared)	\
	__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, _shared, true)

#define for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id)			\
	__for_each_tdp_mmu_root_yield_safe(_kvm, _root, _as_id, false, false)

/*
 * Iterate over all TDP MMU roots.  Requires that mmu_lock be held for write,
 * the implication being that any flow that holds mmu_lock for read is
 * inherently yield-friendly and should use the yield-safe variant above.
 * Holding mmu_lock for write obviates the need for RCU protection as the list
 * is guaranteed to be stable.
 */
#define for_each_tdp_mmu_root(_kvm, _root, _as_id)			\
	list_for_each_entry(_root, &_kvm->arch.tdp_mmu_roots, link)	\
		if (kvm_lockdep_assert_mmu_lock_held(_kvm, false) &&	\
		    kvm_mmu_page_as_id(_root) != _as_id) {		\
		} else

static struct kvm_mmu_page *tdp_mmu_alloc_sp(struct kvm_vcpu *vcpu)
{
	struct kvm_mmu_page *sp;

	sp = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_page_header_cache);
	sp->spt = kvm_mmu_memory_cache_alloc(&vcpu->arch.mmu_shadow_page_cache);

	return sp;
}

static void tdp_mmu_init_sp(struct kvm_mmu_page *sp, tdp_ptep_t sptep,
			    gfn_t gfn, union kvm_mmu_page_role role)
{
	set_page_private(virt_to_page(sp->spt), (unsigned long)sp);

	sp->role = role;
	sp->gfn = gfn;
	sp->ptep = sptep;
	sp->tdp_mmu_page = true;

	trace_kvm_mmu_get_page(sp, true);
}

static void tdp_mmu_init_child_sp(struct kvm_mmu_page *child_sp,
				  struct tdp_iter *iter)
{
	struct kvm_mmu_page *parent_sp;
	union kvm_mmu_page_role role;

	parent_sp = sptep_to_sp(rcu_dereference(iter->sptep));

	role = parent_sp->role;
	role.level--;

	tdp_mmu_init_sp(child_sp, iter->sptep, iter->gfn, role);
}

hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
{
	union kvm_mmu_page_role role = vcpu->arch.mmu->mmu_role.base;
	struct kvm *kvm = vcpu->kvm;
	struct kvm_mmu_page *root;

	lockdep_assert_held_write(&kvm->mmu_lock);

	/*
	 * Check for an existing root before allocating a new one.  Note, the
	 * role check prevents consuming an invalid root.
	 */
	for_each_tdp_mmu_root(kvm, root, kvm_mmu_role_as_id(role)) {
		if (root->role.word == role.word &&
		    kvm_tdp_mmu_get_root(root))
			goto out;
	}

	root = tdp_mmu_alloc_sp(vcpu);
	tdp_mmu_init_sp(root, NULL, 0, role);

	refcount_set(&root->tdp_mmu_root_count, 1);

	spin_lock(&kvm->arch.tdp_mmu_pages_lock);
	list_add_rcu(&root->link, &kvm->arch.tdp_mmu_roots);
	spin_unlock(&kvm->arch.tdp_mmu_pages_lock);

out:
	return __pa(root->spt);
}

static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
				u64 old_spte, u64 new_spte, int level,
				bool shared);

static void handle_changed_spte_acc_track(u64 old_spte, u64 new_spte, int level)
{
	if (!is_shadow_present_pte(old_spte) || !is_last_spte(old_spte, level))
		return;

	if (is_accessed_spte(old_spte) &&
	    (!is_shadow_present_pte(new_spte) || !is_accessed_spte(new_spte) ||
	     spte_to_pfn(old_spte) != spte_to_pfn(new_spte)))
		kvm_set_pfn_accessed(spte_to_pfn(old_spte));
}

static void handle_changed_spte_dirty_log(struct kvm *kvm, int as_id, gfn_t gfn,
					  u64 old_spte, u64 new_spte, int level)
{
	bool pfn_changed;
	struct kvm_memory_slot *slot;

	if (level > PG_LEVEL_4K)
		return;

	pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);

	if ((!is_writable_pte(old_spte) || pfn_changed) &&
	    is_writable_pte(new_spte)) {
		slot = __gfn_to_memslot(__kvm_memslots(kvm, as_id), gfn);
		mark_page_dirty_in_slot(kvm, slot, gfn);
	}
}

/**
 * tdp_mmu_unlink_sp() - Remove a shadow page from the list of used pages
 *
 * @kvm: kvm instance
 * @sp: the page to be removed
 * @shared: This operation may not be running under the exclusive use of
 *	    the MMU lock and the operation must synchronize with other
 *	    threads that might be adding or removing pages.
 */
static void tdp_mmu_unlink_sp(struct kvm *kvm, struct kvm_mmu_page *sp,
			      bool shared)
{
	if (shared)
		spin_lock(&kvm->arch.tdp_mmu_pages_lock);
	else
		lockdep_assert_held_write(&kvm->mmu_lock);

	list_del(&sp->link);
	if (sp->lpage_disallowed)
		unaccount_huge_nx_page(kvm, sp);

	if (shared)
		spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
}

/**
 * handle_removed_pt() - handle a page table removed from the TDP structure
 *
 * @kvm: kvm instance
 * @pt: the page removed from the paging structure
 * @shared: This operation may not be running under the exclusive use
 *	    of the MMU lock and the operation must synchronize with other
 *	    threads that might be modifying SPTEs.
 *
 * Given a page table that has been removed from the TDP paging structure,
 * iterates through the page table to clear SPTEs and free child page tables.
 *
 * Note that pt is passed in as a tdp_ptep_t, but it does not need RCU
 * protection. Since this thread removed it from the paging structure,
 * this thread will be responsible for ensuring the page is freed. Hence the
 * early rcu_dereferences in the function.
 */
static void handle_removed_pt(struct kvm *kvm, tdp_ptep_t pt, bool shared)
{
	struct kvm_mmu_page *sp = sptep_to_sp(rcu_dereference(pt));
	int level = sp->role.level;
	gfn_t base_gfn = sp->gfn;
	int i;

	trace_kvm_mmu_prepare_zap_page(sp);

	tdp_mmu_unlink_sp(kvm, sp, shared);

	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
		u64 *sptep = rcu_dereference(pt) + i;
		gfn_t gfn = base_gfn + i * KVM_PAGES_PER_HPAGE(level);
		u64 old_child_spte;

		if (shared) {
			/*
			 * Set the SPTE to a nonpresent value that other
			 * threads will not overwrite. If the SPTE was
			 * already marked as removed then another thread
			 * handling a page fault could overwrite it, so
			 * set the SPTE until it is set from some other
			 * value to the removed SPTE value.
			 */
			for (;;) {
				old_child_spte = xchg(sptep, REMOVED_SPTE);
				if (!is_removed_spte(old_child_spte))
					break;
				cpu_relax();
			}
		} else {
			/*
			 * If the SPTE is not MMU-present, there is no backing
			 * page associated with the SPTE and so no side effects
			 * that need to be recorded, and exclusive ownership of
			 * mmu_lock ensures the SPTE can't be made present.
			 * Note, zapping MMIO SPTEs is also unnecessary as they
			 * are guarded by the memslots generation, not by being
			 * unreachable.
			 */
			old_child_spte = READ_ONCE(*sptep);
			if (!is_shadow_present_pte(old_child_spte))
				continue;

			/*
			 * Marking the SPTE as a removed SPTE is not
			 * strictly necessary here as the MMU lock will
			 * stop other threads from concurrently modifying
			 * this SPTE. Using the removed SPTE value keeps
			 * the two branches consistent and simplifies
			 * the function.
			 */
			WRITE_ONCE(*sptep, REMOVED_SPTE);
		}
		handle_changed_spte(kvm, kvm_mmu_page_as_id(sp), gfn,
				    old_child_spte, REMOVED_SPTE, level,
				    shared);
	}

	call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback);
}

/**
 * __handle_changed_spte - handle bookkeeping associated with an SPTE change
 * @kvm: kvm instance
 * @as_id: the address space of the paging structure the SPTE was a part of
 * @gfn: the base GFN that was mapped by the SPTE
 * @old_spte: The value of the SPTE before the change
 * @new_spte: The value of the SPTE after the change
 * @level: the level of the PT the SPTE is part of in the paging structure
 * @shared: This operation may not be running under the exclusive use of
 *	    the MMU lock and the operation must synchronize with other
 *	    threads that might be modifying SPTEs.
 *
 * Handle bookkeeping that might result from the modification of a SPTE.
 * This function must be called for all TDP SPTE modifications.
 */
static void __handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
				  u64 old_spte, u64 new_spte, int level,
				  bool shared)
{
	bool was_present = is_shadow_present_pte(old_spte);
	bool is_present = is_shadow_present_pte(new_spte);
	bool was_leaf = was_present && is_last_spte(old_spte, level);
	bool is_leaf = is_present && is_last_spte(new_spte, level);
	bool pfn_changed = spte_to_pfn(old_spte) != spte_to_pfn(new_spte);

	WARN_ON(level > PT64_ROOT_MAX_LEVEL);
	WARN_ON(level < PG_LEVEL_4K);
	WARN_ON(gfn & (KVM_PAGES_PER_HPAGE(level) - 1));

	/*
	 * If this warning were to trigger it would indicate that there was a
	 * missing MMU notifier or a race with some notifier handler.
	 * A present, leaf SPTE should never be directly replaced with another
	 * present leaf SPTE pointing to a different PFN. A notifier handler
	 * should be zapping the SPTE before the main MM's page table is
	 * changed, or the SPTE should be zeroed, and the TLBs flushed by the
	 * thread before replacement.
	 */
	if (was_leaf && is_leaf && pfn_changed) {
		pr_err("Invalid SPTE change: cannot replace a present leaf\n"
		       "SPTE with another present leaf SPTE mapping a\n"
		       "different PFN!\n"
		       "as_id: %d gfn: %llx old_spte: %llx new_spte: %llx level: %d",
		       as_id, gfn, old_spte, new_spte, level);

		/*
		 * Crash the host to prevent error propagation and guest data
		 * corruption.
		 */
		BUG();
	}

	if (old_spte == new_spte)
		return;

	trace_kvm_tdp_mmu_spte_changed(as_id, gfn, level, old_spte, new_spte);

	if (is_leaf)
		check_spte_writable_invariants(new_spte);

	/*
	 * The only times a SPTE should be changed from a non-present to
	 * non-present state is when an MMIO entry is installed/modified/
	 * removed. In that case, there is nothing to do here.
	 */
	if (!was_present && !is_present) {
		/*
		 * If this change does not involve a MMIO SPTE or removed SPTE,
		 * it is unexpected. Log the change, though it should not
		 * impact the guest since both the former and current SPTEs
		 * are nonpresent.
		 */
		if (WARN_ON(!is_mmio_spte(old_spte) &&
			    !is_mmio_spte(new_spte) &&
			    !is_removed_spte(new_spte)))
			pr_err("Unexpected SPTE change! Nonpresent SPTEs\n"
			       "should not be replaced with another,\n"
			       "different nonpresent SPTE, unless one or both\n"
			       "are MMIO SPTEs, or the new SPTE is\n"
			       "a temporary removed SPTE.\n"
			       "as_id: %d gfn: %llx old_spte: %llx new_spte: %llx level: %d",
			       as_id, gfn, old_spte, new_spte, level);
		return;
	}

	if (is_leaf != was_leaf)
		kvm_update_page_stats(kvm, level, is_leaf ? 1 : -1);

	if (was_leaf && is_dirty_spte(old_spte) &&
	    (!is_present || !is_dirty_spte(new_spte) || pfn_changed))
		kvm_set_pfn_dirty(spte_to_pfn(old_spte));

	/*
	 * Recursively handle child PTs if the change removed a subtree from
	 * the paging structure.  Note the WARN on the PFN changing without the
	 * SPTE being converted to a hugepage (leaf) or being zapped.  Shadow
	 * pages are kernel allocations and should never be migrated.
	 */
	if (was_present && !was_leaf &&
	    (is_leaf || !is_present || WARN_ON_ONCE(pfn_changed)))
		handle_removed_pt(kvm, spte_to_child_pt(old_spte, level), shared);
}

static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn,
				u64 old_spte, u64 new_spte, int level,
				bool shared)
{
	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level,
			      shared);
	handle_changed_spte_acc_track(old_spte, new_spte, level);
	handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte,
				      new_spte, level);
}

/*
 * tdp_mmu_set_spte_atomic - Set a TDP MMU SPTE atomically
 * and handle the associated bookkeeping.  Do not mark the page dirty
 * in KVM's dirty bitmaps.
 *
 * If setting the SPTE fails because it has changed, iter->old_spte will be
 * refreshed to the current value of the spte.
 *
 * @kvm: kvm instance
 * @iter: a tdp_iter instance currently on the SPTE that should be set
 * @new_spte: The value the SPTE should be set to
 * Return:
 * * 0      - If the SPTE was set.
 * * -EBUSY - If the SPTE cannot be set. In this case this function will have
 *            no side-effects other than setting iter->old_spte to the last
 *            known value of the spte.
 */
static inline int tdp_mmu_set_spte_atomic(struct kvm *kvm,
					  struct tdp_iter *iter,
					  u64 new_spte)
{
	u64 *sptep = rcu_dereference(iter->sptep);
	u64 old_spte;

	/*
	 * The caller is responsible for ensuring the old SPTE is not a REMOVED
	 * SPTE.  KVM should never attempt to zap or manipulate a REMOVED SPTE,
	 * and pre-checking before inserting a new SPTE is advantageous as it
	 * avoids unnecessary work.
	 */
	WARN_ON_ONCE(iter->yielded || is_removed_spte(iter->old_spte));

	lockdep_assert_held_read(&kvm->mmu_lock);

	/*
	 * Note, fast_pf_fix_direct_spte() can also modify TDP MMU SPTEs and
	 * does not hold the mmu_lock.
	 */
	old_spte = cmpxchg64(sptep, iter->old_spte, new_spte);
	if (old_spte != iter->old_spte) {
		/*
		 * The page table entry was modified by a different logical
		 * CPU. Refresh iter->old_spte with the current value so the
		 * caller operates on fresh data, e.g. if it retries
		 * tdp_mmu_set_spte_atomic().
		 */
		iter->old_spte = old_spte;
		return -EBUSY;
	}

	__handle_changed_spte(kvm, iter->as_id, iter->gfn, iter->old_spte,
			      new_spte, iter->level, true);
	handle_changed_spte_acc_track(iter->old_spte, new_spte, iter->level);

	return 0;
}

static inline int tdp_mmu_zap_spte_atomic(struct kvm *kvm,
					  struct tdp_iter *iter)
{
	int ret;

	/*
	 * Freeze the SPTE by setting it to a special,
	 * non-present value. This will stop other threads from
	 * immediately installing a present entry in its place
	 * before the TLBs are flushed.
	 */
	ret = tdp_mmu_set_spte_atomic(kvm, iter, REMOVED_SPTE);
	if (ret)
		return ret;

	kvm_flush_remote_tlbs_with_address(kvm, iter->gfn,
					   KVM_PAGES_PER_HPAGE(iter->level));

	/*
	 * No other thread can overwrite the removed SPTE as they
	 * must either wait on the MMU lock or use
	 * tdp_mmu_set_spte_atomic which will not overwrite the
	 * special removed SPTE value. No bookkeeping is needed
	 * here since the SPTE is going from non-present
	 * to non-present.
	 */
	kvm_tdp_mmu_write_spte(iter->sptep, 0);

	return 0;
}


/*
 * __tdp_mmu_set_spte - Set a TDP MMU SPTE and handle the associated bookkeeping
 * @kvm:	      KVM instance
 * @as_id:	      Address space ID, i.e. regular vs. SMM
 * @sptep:	      Pointer to the SPTE
 * @old_spte:	      The current value of the SPTE
 * @new_spte:	      The new value that will be set for the SPTE
 * @gfn:	      The base GFN that was (or will be) mapped by the SPTE
 * @level:	      The level _containing_ the SPTE (its parent PT's level)
 * @record_acc_track: Notify the MM subsystem of changes to the accessed state
 *		      of the page. Should be set unless handling an MMU
 *		      notifier for access tracking. Leaving record_acc_track
 *		      unset in that case prevents page accesses from being
 *		      double counted.
 * @record_dirty_log: Record the page as dirty in the dirty bitmap if
 *		      appropriate for the change being made. Should be set
 *		      unless performing certain dirty logging operations.
 *		      Leaving record_dirty_log unset in that case prevents page
 *		      writes from being double counted.
 */
static void __tdp_mmu_set_spte(struct kvm *kvm, int as_id, tdp_ptep_t sptep,
			       u64 old_spte, u64 new_spte, gfn_t gfn, int level,
			       bool record_acc_track, bool record_dirty_log)
{
	lockdep_assert_held_write(&kvm->mmu_lock);

	/*
	 * No thread should be using this function to set SPTEs to or from the
	 * temporary removed SPTE value.
	 * If operating under the MMU lock in read mode, tdp_mmu_set_spte_atomic
	 * should be used. If operating under the MMU lock in write mode, the
	 * use of the removed SPTE should not be necessary.
	 */
	WARN_ON(is_removed_spte(old_spte) || is_removed_spte(new_spte));

	kvm_tdp_mmu_write_spte(sptep, new_spte);

	__handle_changed_spte(kvm, as_id, gfn, old_spte, new_spte, level, false);

	if (record_acc_track)
		handle_changed_spte_acc_track(old_spte, new_spte, level);
	if (record_dirty_log)
		handle_changed_spte_dirty_log(kvm, as_id, gfn, old_spte,
					      new_spte, level);
}

static inline void _tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
				     u64 new_spte, bool record_acc_track,
				     bool record_dirty_log)
{
	WARN_ON_ONCE(iter->yielded);

	__tdp_mmu_set_spte(kvm, iter->as_id, iter->sptep, iter->old_spte,
			   new_spte, iter->gfn, iter->level,
			   record_acc_track, record_dirty_log);
}

static inline void tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
				    u64 new_spte)
{
	_tdp_mmu_set_spte(kvm, iter, new_spte, true, true);
}

static inline void tdp_mmu_set_spte_no_acc_track(struct kvm *kvm,
						 struct tdp_iter *iter,
						 u64 new_spte)
{
	_tdp_mmu_set_spte(kvm, iter, new_spte, false, true);
}

static inline void tdp_mmu_set_spte_no_dirty_log(struct kvm *kvm,
						 struct tdp_iter *iter,
						 u64 new_spte)
{
	_tdp_mmu_set_spte(kvm, iter, new_spte, true, false);
}

#define tdp_root_for_each_pte(_iter, _root, _start, _end) \
	for_each_tdp_pte(_iter, _root, _start, _end)

#define tdp_root_for_each_leaf_pte(_iter, _root, _start, _end)	\
	tdp_root_for_each_pte(_iter, _root, _start, _end)		\
		if (!is_shadow_present_pte(_iter.old_spte) ||		\
		    !is_last_spte(_iter.old_spte, _iter.level))		\
			continue;					\
		else

#define tdp_mmu_for_each_pte(_iter, _mmu, _start, _end)		\
	for_each_tdp_pte(_iter, to_shadow_page(_mmu->root.hpa), _start, _end)

/*
 * Yield if the MMU lock is contended or this thread needs to return control
 * to the scheduler.
 *
 * If this function should yield and flush is set, it will perform a remote
 * TLB flush before yielding.
 *
 * If this function yields, iter->yielded is set and the caller must skip to
 * the next iteration, where tdp_iter_next() will reset the tdp_iter's walk
 * over the paging structures to allow the iterator to continue its traversal
 * from the paging structure root.
 *
 * Returns true if this function yielded.
 */
static inline bool __must_check tdp_mmu_iter_cond_resched(struct kvm *kvm,
							  struct tdp_iter *iter,
							  bool flush, bool shared)
{
	WARN_ON(iter->yielded);

	/* Ensure forward progress has been made before yielding. */
	if (iter->next_last_level_gfn == iter->yielded_gfn)
		return false;

	if (need_resched() || rwlock_needbreak(&kvm->mmu_lock)) {
		if (flush)
			kvm_flush_remote_tlbs(kvm);

		rcu_read_unlock();

		if (shared)
			cond_resched_rwlock_read(&kvm->mmu_lock);
		else
			cond_resched_rwlock_write(&kvm->mmu_lock);

		rcu_read_lock();

		WARN_ON(iter->gfn > iter->next_last_level_gfn);

		iter->yielded = true;
	}

	return iter->yielded;
}

static inline gfn_t tdp_mmu_max_gfn_host(void)
{
	/*
	 * Bound TDP MMU walks at host.MAXPHYADDR, guest accesses beyond that
	 * will hit a #PF(RSVD) and never hit an EPT Violation/Misconfig / #NPF,
	 * and so KVM will never install a SPTE for such addresses.
	 */
	return 1ULL << (shadow_phys_bits - PAGE_SHIFT);
}

static void __tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
			       bool shared, int zap_level)
{
	struct tdp_iter iter;

	gfn_t end = tdp_mmu_max_gfn_host();
	gfn_t start = 0;

	for_each_tdp_pte_min_level(iter, root, zap_level, start, end) {
retry:
		if (tdp_mmu_iter_cond_resched(kvm, &iter, false, shared))
			continue;

		if (!is_shadow_present_pte(iter.old_spte))
			continue;

		if (iter.level > zap_level)
			continue;

		if (!shared)
			tdp_mmu_set_spte(kvm, &iter, 0);
		else if (tdp_mmu_set_spte_atomic(kvm, &iter, 0))
			goto retry;
	}
}

static void tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
			     bool shared)
{

	/*
	 * The root must have an elevated refcount so that it's reachable via
	 * mmu_notifier callbacks, which allows this path to yield and drop
	 * mmu_lock.  When handling an unmap/release mmu_notifier command, KVM
	 * must drop all references to relevant pages prior to completing the
	 * callback.  Dropping mmu_lock with an unreachable root would result
	 * in zapping SPTEs after a relevant mmu_notifier callback completes
	 * and lead to use-after-free as zapping a SPTE triggers "writeback" of
	 * dirty accessed bits to the SPTE's associated struct page.
	 */
	WARN_ON_ONCE(!refcount_read(&root->tdp_mmu_root_count));

	kvm_lockdep_assert_mmu_lock_held(kvm, shared);

	rcu_read_lock();

	/*
	 * To avoid RCU stalls due to recursively removing huge swaths of SPs,
	 * split the zap into two passes.  On the first pass, zap at the 1gb
	 * level, and then zap top-level SPs on the second pass.  "1gb" is not
	 * arbitrary, as KVM must be able to zap a 1gb shadow page without
	 * inducing a stall to allow in-place replacement with a 1gb hugepage.
	 *
	 * Because zapping a SP recurses on its children, stepping down to
	 * PG_LEVEL_4K in the iterator itself is unnecessary.
	 */
	__tdp_mmu_zap_root(kvm, root, shared, PG_LEVEL_1G);
	__tdp_mmu_zap_root(kvm, root, shared, root->role.level);

	rcu_read_unlock();
}

bool kvm_tdp_mmu_zap_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
{
	u64 old_spte;

	/*
	 * This helper intentionally doesn't allow zapping a root shadow page,
	 * which doesn't have a parent page table and thus no associated entry.
	 */
	if (WARN_ON_ONCE(!sp->ptep))
		return false;

	old_spte = kvm_tdp_mmu_read_spte(sp->ptep);
	if (WARN_ON_ONCE(!is_shadow_present_pte(old_spte)))
		return false;

	__tdp_mmu_set_spte(kvm, kvm_mmu_page_as_id(sp), sp->ptep, old_spte, 0,
			   sp->gfn, sp->role.level + 1, true, true);

	return true;
}

/*
 * Zap leafs SPTEs for the range of gfns, [start, end). Returns true if SPTEs
 * have been cleared and a TLB flush is needed before releasing the MMU lock.
 *
 * If can_yield is true, will release the MMU lock and reschedule if the
 * scheduler needs the CPU or there is contention on the MMU lock. If this
 * function cannot yield, it will not release the MMU lock or reschedule and
 * the caller must ensure it does not supply too large a GFN range, or the
 * operation can cause a soft lockup.
 */
static bool tdp_mmu_zap_leafs(struct kvm *kvm, struct kvm_mmu_page *root,
			      gfn_t start, gfn_t end, bool can_yield, bool flush)
{
	struct tdp_iter iter;

	end = min(end, tdp_mmu_max_gfn_host());

	lockdep_assert_held_write(&kvm->mmu_lock);

	rcu_read_lock();

	for_each_tdp_pte_min_level(iter, root, PG_LEVEL_4K, start, end) {
		if (can_yield &&
		    tdp_mmu_iter_cond_resched(kvm, &iter, flush, false)) {
			flush = false;
			continue;
		}

		if (!is_shadow_present_pte(iter.old_spte) ||
		    !is_last_spte(iter.old_spte, iter.level))
			continue;

		tdp_mmu_set_spte(kvm, &iter, 0);
		flush = true;
	}

	rcu_read_unlock();

	/*
	 * Because this flow zaps _only_ leaf SPTEs, the caller doesn't need
	 * to provide RCU protection as no 'struct kvm_mmu_page' will be freed.
	 */
	return flush;
}

/*
 * Tears down the mappings for the range of gfns, [start, end), and frees the
 * non-root pages mapping GFNs strictly within that range. Returns true if
 * SPTEs have been cleared and a TLB flush is needed before releasing the
 * MMU lock.
 */
bool kvm_tdp_mmu_zap_leafs(struct kvm *kvm, int as_id, gfn_t start, gfn_t end,
			   bool can_yield, bool flush)
{
	struct kvm_mmu_page *root;

	for_each_tdp_mmu_root_yield_safe(kvm, root, as_id)
		flush = tdp_mmu_zap_leafs(kvm, root, start, end, can_yield, flush);

	return flush;
}

void kvm_tdp_mmu_zap_all(struct kvm *kvm)
{
	struct kvm_mmu_page *root;
	int i;

	/*
	 * Zap all roots, including invalid roots, as all SPTEs must be dropped
	 * before returning to the caller.  Zap directly even if the root is
	 * also being zapped by a worker.  Walking zapped top-level SPTEs isn't
	 * all that expensive and mmu_lock is already held, which means the
	 * worker has yielded, i.e. flushing the work instead of zapping here
	 * isn't guaranteed to be any faster.
	 *
	 * A TLB flush is unnecessary, KVM zaps everything if and only the VM
	 * is being destroyed or the userspace VMM has exited.  In both cases,
	 * KVM_RUN is unreachable, i.e. no vCPUs will ever service the request.
	 */
	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
		for_each_tdp_mmu_root_yield_safe(kvm, root, i)
			tdp_mmu_zap_root(kvm, root, false);
	}
}

/*
 * Zap all invalidated roots to ensure all SPTEs are dropped before the "fast
 * zap" completes.
 */
void kvm_tdp_mmu_zap_invalidated_roots(struct kvm *kvm)
{
	flush_workqueue(kvm->arch.tdp_mmu_zap_wq);
}

/*
 * Mark each TDP MMU root as invalid to prevent vCPUs from reusing a root that
 * is about to be zapped, e.g. in response to a memslots update.  The actual
 * zapping is performed asynchronously, so a reference is taken on all roots.
 * Using a separate workqueue makes it easy to ensure that the destruction is
 * performed before the "fast zap" completes, without keeping a separate list
 * of invalidated roots; the list is effectively the list of work items in
 * the workqueue.
 *
 * Get a reference even if the root is already invalid, the asynchronous worker
 * assumes it was gifted a reference to the root it processes.  Because mmu_lock
 * is held for write, it should be impossible to observe a root with zero refcount,
 * i.e. the list of roots cannot be stale.
 *
 * This has essentially the same effect for the TDP MMU
 * as updating mmu_valid_gen does for the shadow MMU.
 */
void kvm_tdp_mmu_invalidate_all_roots(struct kvm *kvm)
{
	struct kvm_mmu_page *root;

	lockdep_assert_held_write(&kvm->mmu_lock);
	list_for_each_entry(root, &kvm->arch.tdp_mmu_roots, link) {
		if (!root->role.invalid &&
		    !WARN_ON_ONCE(!kvm_tdp_mmu_get_root(root))) {
			root->role.invalid = true;
			tdp_mmu_schedule_zap_root(kvm, root);
		}
	}
}

/*
 * Installs a last-level SPTE to handle a TDP page fault.
 * (NPT/EPT violation/misconfiguration)
 */
static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
					  struct kvm_page_fault *fault,
					  struct tdp_iter *iter)
{
	struct kvm_mmu_page *sp = sptep_to_sp(rcu_dereference(iter->sptep));
	u64 new_spte;
	int ret = RET_PF_FIXED;
	bool wrprot = false;

	WARN_ON(sp->role.level != fault->goal_level);
	if (unlikely(!fault->slot))
		new_spte = make_mmio_spte(vcpu, iter->gfn, ACC_ALL);
	else
		wrprot = make_spte(vcpu, sp, fault->slot, ACC_ALL, iter->gfn,
					 fault->pfn, iter->old_spte, fault->prefetch, true,
					 fault->map_writable, &new_spte);

	if (new_spte == iter->old_spte)
		ret = RET_PF_SPURIOUS;
	else if (tdp_mmu_set_spte_atomic(vcpu->kvm, iter, new_spte))
		return RET_PF_RETRY;
	else if (is_shadow_present_pte(iter->old_spte) &&
		 !is_last_spte(iter->old_spte, iter->level))
		kvm_flush_remote_tlbs_with_address(vcpu->kvm, sp->gfn,
						   KVM_PAGES_PER_HPAGE(iter->level + 1));

	/*
	 * If the page fault was caused by a write but the page is write
	 * protected, emulation is needed. If the emulation was skipped,
	 * the vCPU would have the same fault again.
	 */
	if (wrprot) {
		if (fault->write)
			ret = RET_PF_EMULATE;
	}

	/* If a MMIO SPTE is installed, the MMIO will need to be emulated. */
	if (unlikely(is_mmio_spte(new_spte))) {
		trace_mark_mmio_spte(rcu_dereference(iter->sptep), iter->gfn,
				     new_spte);
		ret = RET_PF_EMULATE;
	} else {
		trace_kvm_mmu_set_spte(iter->level, iter->gfn,
				       rcu_dereference(iter->sptep));
	}

	/*
	 * Increase pf_fixed in both RET_PF_EMULATE and RET_PF_FIXED to be
	 * consistent with legacy MMU behavior.
	 */
	if (ret != RET_PF_SPURIOUS)
		vcpu->stat.pf_fixed++;

	return ret;
}

/*
 * tdp_mmu_link_sp - Replace the given spte with an spte pointing to the
 * provided page table.
 *
 * @kvm: kvm instance
 * @iter: a tdp_iter instance currently on the SPTE that should be set
 * @sp: The new TDP page table to install.
 * @account_nx: True if this page table is being installed to split a
 *              non-executable huge page.
 * @shared: This operation is running under the MMU lock in read mode.
 *
 * Returns: 0 if the new page table was installed. Non-0 if the page table
 *          could not be installed (e.g. the atomic compare-exchange failed).
 */
static int tdp_mmu_link_sp(struct kvm *kvm, struct tdp_iter *iter,
			   struct kvm_mmu_page *sp, bool account_nx,
			   bool shared)
{
	u64 spte = make_nonleaf_spte(sp->spt, !shadow_accessed_mask);
	int ret = 0;

	if (shared) {
		ret = tdp_mmu_set_spte_atomic(kvm, iter, spte);
		if (ret)
			return ret;
	} else {
		tdp_mmu_set_spte(kvm, iter, spte);
	}

	spin_lock(&kvm->arch.tdp_mmu_pages_lock);
	list_add(&sp->link, &kvm->arch.tdp_mmu_pages);
	if (account_nx)
		account_huge_nx_page(kvm, sp);
	spin_unlock(&kvm->arch.tdp_mmu_pages_lock);

	return 0;
}

/*
 * Handle a TDP page fault (NPT/EPT violation/misconfiguration) by installing
 * page tables and SPTEs to translate the faulting guest physical address.
 */
int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
	struct kvm_mmu *mmu = vcpu->arch.mmu;
	struct tdp_iter iter;
	struct kvm_mmu_page *sp;
	int ret;

	kvm_mmu_hugepage_adjust(vcpu, fault);

	trace_kvm_mmu_spte_requested(fault);

	rcu_read_lock();

	tdp_mmu_for_each_pte(iter, mmu, fault->gfn, fault->gfn + 1) {
		if (fault->nx_huge_page_workaround_enabled)
			disallowed_hugepage_adjust(fault, iter.old_spte, iter.level);

		if (iter.level == fault->goal_level)
			break;

		/*
		 * If there is an SPTE mapping a large page at a higher level
		 * than the target, that SPTE must be cleared and replaced
		 * with a non-leaf SPTE.
		 */
		if (is_shadow_present_pte(iter.old_spte) &&
		    is_large_pte(iter.old_spte)) {
			if (tdp_mmu_zap_spte_atomic(vcpu->kvm, &iter))
				break;

			/*
			 * The iter must explicitly re-read the spte here
			 * because the new value informs the !present
			 * path below.
			 */
			iter.old_spte = kvm_tdp_mmu_read_spte(iter.sptep);
		}

		if (!is_shadow_present_pte(iter.old_spte)) {
			bool account_nx = fault->huge_page_disallowed &&
					  fault->req_level >= iter.level;

			/*
			 * If SPTE has been frozen by another thread, just
			 * give up and retry, avoiding unnecessary page table
			 * allocation and free.
			 */
			if (is_removed_spte(iter.old_spte))
				break;

			sp = tdp_mmu_alloc_sp(vcpu);
			tdp_mmu_init_child_sp(sp, &iter);

			if (tdp_mmu_link_sp(vcpu->kvm, &iter, sp, account_nx, true)) {
				tdp_mmu_free_sp(sp);
				break;
			}
		}
	}

	/*
	 * Force the guest to retry the access if the upper level SPTEs aren't
	 * in place, or if the target leaf SPTE is frozen by another CPU.
	 */
	if (iter.level != fault->goal_level || is_removed_spte(iter.old_spte)) {
		rcu_read_unlock();
		return RET_PF_RETRY;
	}

	ret = tdp_mmu_map_handle_target_level(vcpu, fault, &iter);
	rcu_read_unlock();

	return ret;
}

bool kvm_tdp_mmu_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range,
				 bool flush)
{
	return kvm_tdp_mmu_zap_leafs(kvm, range->slot->as_id, range->start,
				     range->end, range->may_block, flush);
}

typedef bool (*tdp_handler_t)(struct kvm *kvm, struct tdp_iter *iter,
			      struct kvm_gfn_range *range);

static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm,
						   struct kvm_gfn_range *range,
						   tdp_handler_t handler)
{
	struct kvm_mmu_page *root;
	struct tdp_iter iter;
	bool ret = false;

	/*
	 * Don't support rescheduling, none of the MMU notifiers that funnel
	 * into this helper allow blocking; it'd be dead, wasteful code.
	 */
	for_each_tdp_mmu_root(kvm, root, range->slot->as_id) {
		rcu_read_lock();

		tdp_root_for_each_leaf_pte(iter, root, range->start, range->end)
			ret |= handler(kvm, &iter, range);

		rcu_read_unlock();
	}

	return ret;
}

/*
 * Mark the SPTEs range of GFNs [start, end) unaccessed and return non-zero
 * if any of the GFNs in the range have been accessed.
 */
static bool age_gfn_range(struct kvm *kvm, struct tdp_iter *iter,
			  struct kvm_gfn_range *range)
{
	u64 new_spte = 0;

	/* If we have a non-accessed entry we don't need to change the pte. */
	if (!is_accessed_spte(iter->old_spte))
		return false;

	new_spte = iter->old_spte;

	if (spte_ad_enabled(new_spte)) {
		new_spte &= ~shadow_accessed_mask;
	} else {
		/*
		 * Capture the dirty status of the page, so that it doesn't get
		 * lost when the SPTE is marked for access tracking.
		 */
		if (is_writable_pte(new_spte))
			kvm_set_pfn_dirty(spte_to_pfn(new_spte));

		new_spte = mark_spte_for_access_track(new_spte);
	}

	tdp_mmu_set_spte_no_acc_track(kvm, iter, new_spte);

	return true;
}

bool kvm_tdp_mmu_age_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
{
	return kvm_tdp_mmu_handle_gfn(kvm, range, age_gfn_range);
}

static bool test_age_gfn(struct kvm *kvm, struct tdp_iter *iter,
			 struct kvm_gfn_range *range)
{
	return is_accessed_spte(iter->old_spte);
}

bool kvm_tdp_mmu_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
	return kvm_tdp_mmu_handle_gfn(kvm, range, test_age_gfn);
}

static bool set_spte_gfn(struct kvm *kvm, struct tdp_iter *iter,
			 struct kvm_gfn_range *range)
{
	u64 new_spte;

	/* Huge pages aren't expected to be modified without first being zapped. */
	WARN_ON(pte_huge(range->pte) || range->start + 1 != range->end);

	if (iter->level != PG_LEVEL_4K ||
	    !is_shadow_present_pte(iter->old_spte))
		return false;

	/*
	 * Note, when changing a read-only SPTE, it's not strictly necessary to
	 * zero the SPTE before setting the new PFN, but doing so preserves the
	 * invariant that the PFN of a present * leaf SPTE can never change.
	 * See __handle_changed_spte().
	 */
	tdp_mmu_set_spte(kvm, iter, 0);

	if (!pte_write(range->pte)) {
		new_spte = kvm_mmu_changed_pte_notifier_make_spte(iter->old_spte,
								  pte_pfn(range->pte));

		tdp_mmu_set_spte(kvm, iter, new_spte);
	}

	return true;
}

/*
 * Handle the changed_pte MMU notifier for the TDP MMU.
 * data is a pointer to the new pte_t mapping the HVA specified by the MMU
 * notifier.
 * Returns non-zero if a flush is needed before releasing the MMU lock.
 */
bool kvm_tdp_mmu_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
{
	/*
	 * No need to handle the remote TLB flush under RCU protection, the
	 * target SPTE _must_ be a leaf SPTE, i.e. cannot result in freeing a
	 * shadow page.  See the WARN on pfn_changed in __handle_changed_spte().
	 */
	return kvm_tdp_mmu_handle_gfn(kvm, range, set_spte_gfn);
}

/*
 * Remove write access from all SPTEs at or above min_level that map GFNs
 * [start, end). Returns true if an SPTE has been changed and the TLBs need to
 * be flushed.
 */
static bool wrprot_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
			     gfn_t start, gfn_t end, int min_level)
{
	struct tdp_iter iter;
	u64 new_spte;
	bool spte_set = false;

	rcu_read_lock();

	BUG_ON(min_level > KVM_MAX_HUGEPAGE_LEVEL);

	for_each_tdp_pte_min_level(iter, root, min_level, start, end) {
retry:
		if (tdp_mmu_iter_cond_resched(kvm, &iter, false, true))
			continue;

		if (!is_shadow_present_pte(iter.old_spte) ||
		    !is_last_spte(iter.old_spte, iter.level) ||
		    !(iter.old_spte & PT_WRITABLE_MASK))
			continue;

		new_spte = iter.old_spte & ~PT_WRITABLE_MASK;

		if (tdp_mmu_set_spte_atomic(kvm, &iter, new_spte))
			goto retry;

		spte_set = true;
	}

	rcu_read_unlock();
	return spte_set;
}

/*
 * Remove write access from all the SPTEs mapping GFNs in the memslot. Will
 * only affect leaf SPTEs down to min_level.
 * Returns true if an SPTE has been changed and the TLBs need to be flushed.
 */
bool kvm_tdp_mmu_wrprot_slot(struct kvm *kvm,
			     const struct kvm_memory_slot *slot, int min_level)
{
	struct kvm_mmu_page *root;
	bool spte_set = false;

	lockdep_assert_held_read(&kvm->mmu_lock);

	for_each_valid_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, true)
		spte_set |= wrprot_gfn_range(kvm, root, slot->base_gfn,
			     slot->base_gfn + slot->npages, min_level);

	return spte_set;
}

static struct kvm_mmu_page *__tdp_mmu_alloc_sp_for_split(gfp_t gfp)
{
	struct kvm_mmu_page *sp;

	gfp |= __GFP_ZERO;

	sp = kmem_cache_alloc(mmu_page_header_cache, gfp);
	if (!sp)
		return NULL;

	sp->spt = (void *)__get_free_page(gfp);
	if (!sp->spt) {
		kmem_cache_free(mmu_page_header_cache, sp);
		return NULL;
	}

	return sp;
}

static struct kvm_mmu_page *tdp_mmu_alloc_sp_for_split(struct kvm *kvm,
						       struct tdp_iter *iter,
						       bool shared)
{
	struct kvm_mmu_page *sp;

	/*
	 * Since we are allocating while under the MMU lock we have to be
	 * careful about GFP flags. Use GFP_NOWAIT to avoid blocking on direct
	 * reclaim and to avoid making any filesystem callbacks (which can end
	 * up invoking KVM MMU notifiers, resulting in a deadlock).
	 *
	 * If this allocation fails we drop the lock and retry with reclaim
	 * allowed.
	 */
	sp = __tdp_mmu_alloc_sp_for_split(GFP_NOWAIT | __GFP_ACCOUNT);
	if (sp)
		return sp;

	rcu_read_unlock();

	if (shared)
		read_unlock(&kvm->mmu_lock);
	else
		write_unlock(&kvm->mmu_lock);

	iter->yielded = true;
	sp = __tdp_mmu_alloc_sp_for_split(GFP_KERNEL_ACCOUNT);

	if (shared)
		read_lock(&kvm->mmu_lock);
	else
		write_lock(&kvm->mmu_lock);

	rcu_read_lock();

	return sp;
}

static int tdp_mmu_split_huge_page(struct kvm *kvm, struct tdp_iter *iter,
				   struct kvm_mmu_page *sp, bool shared)
{
	const u64 huge_spte = iter->old_spte;
	const int level = iter->level;
	int ret, i;

	tdp_mmu_init_child_sp(sp, iter);

	/*
	 * No need for atomics when writing to sp->spt since the page table has
	 * not been linked in yet and thus is not reachable from any other CPU.
	 */
	for (i = 0; i < PT64_ENT_PER_PAGE; i++)
		sp->spt[i] = make_huge_page_split_spte(huge_spte, level, i);

	/*
	 * Replace the huge spte with a pointer to the populated lower level
	 * page table. Since we are making this change without a TLB flush vCPUs
	 * will see a mix of the split mappings and the original huge mapping,
	 * depending on what's currently in their TLB. This is fine from a
	 * correctness standpoint since the translation will be the same either
	 * way.
	 */
	ret = tdp_mmu_link_sp(kvm, iter, sp, false, shared);
	if (ret)
		goto out;

	/*
	 * tdp_mmu_link_sp_atomic() will handle subtracting the huge page we
	 * are overwriting from the page stats. But we have to manually update
	 * the page stats with the new present child pages.
	 */
	kvm_update_page_stats(kvm, level - 1, PT64_ENT_PER_PAGE);

out:
	trace_kvm_mmu_split_huge_page(iter->gfn, huge_spte, level, ret);
	return ret;
}

static int tdp_mmu_split_huge_pages_root(struct kvm *kvm,
					 struct kvm_mmu_page *root,
					 gfn_t start, gfn_t end,
					 int target_level, bool shared)
{
	struct kvm_mmu_page *sp = NULL;
	struct tdp_iter iter;
	int ret = 0;

	rcu_read_lock();

	/*
	 * Traverse the page table splitting all huge pages above the target
	 * level into one lower level. For example, if we encounter a 1GB page
	 * we split it into 512 2MB pages.
	 *
	 * Since the TDP iterator uses a pre-order traversal, we are guaranteed
	 * to visit an SPTE before ever visiting its children, which means we
	 * will correctly recursively split huge pages that are more than one
	 * level above the target level (e.g. splitting a 1GB to 512 2MB pages,
	 * and then splitting each of those to 512 4KB pages).
	 */
	for_each_tdp_pte_min_level(iter, root, target_level + 1, start, end) {
retry:
		if (tdp_mmu_iter_cond_resched(kvm, &iter, false, shared))
			continue;

		if (!is_shadow_present_pte(iter.old_spte) || !is_large_pte(iter.old_spte))
			continue;

		if (!sp) {
			sp = tdp_mmu_alloc_sp_for_split(kvm, &iter, shared);
			if (!sp) {
				ret = -ENOMEM;
				trace_kvm_mmu_split_huge_page(iter.gfn,
							      iter.old_spte,
							      iter.level, ret);
				break;
			}

			if (iter.yielded)
				continue;
		}

		if (tdp_mmu_split_huge_page(kvm, &iter, sp, shared))
			goto retry;

		sp = NULL;
	}

	rcu_read_unlock();

	/*
	 * It's possible to exit the loop having never used the last sp if, for
	 * example, a vCPU doing HugePage NX splitting wins the race and
	 * installs its own sp in place of the last sp we tried to split.
	 */
	if (sp)
		tdp_mmu_free_sp(sp);

	return ret;
}


/*
 * Try to split all huge pages mapped by the TDP MMU down to the target level.
 */
void kvm_tdp_mmu_try_split_huge_pages(struct kvm *kvm,
				      const struct kvm_memory_slot *slot,
				      gfn_t start, gfn_t end,
				      int target_level, bool shared)
{
	struct kvm_mmu_page *root;
	int r = 0;

	kvm_lockdep_assert_mmu_lock_held(kvm, shared);

	for_each_valid_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, shared) {
		r = tdp_mmu_split_huge_pages_root(kvm, root, start, end, target_level, shared);
		if (r) {
			kvm_tdp_mmu_put_root(kvm, root, shared);
			break;
		}
	}
}

/*
 * Clear the dirty status of all the SPTEs mapping GFNs in the memslot. If
 * AD bits are enabled, this will involve clearing the dirty bit on each SPTE.
 * If AD bits are not enabled, this will require clearing the writable bit on
 * each SPTE. Returns true if an SPTE has been changed and the TLBs need to
 * be flushed.
 */
static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
			   gfn_t start, gfn_t end)
{
	struct tdp_iter iter;
	u64 new_spte;
	bool spte_set = false;

	rcu_read_lock();

	tdp_root_for_each_leaf_pte(iter, root, start, end) {
retry:
		if (tdp_mmu_iter_cond_resched(kvm, &iter, false, true))
			continue;

		if (!is_shadow_present_pte(iter.old_spte))
			continue;

		if (spte_ad_need_write_protect(iter.old_spte)) {
			if (is_writable_pte(iter.old_spte))
				new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
			else
				continue;
		} else {
			if (iter.old_spte & shadow_dirty_mask)
				new_spte = iter.old_spte & ~shadow_dirty_mask;
			else
				continue;
		}

		if (tdp_mmu_set_spte_atomic(kvm, &iter, new_spte))
			goto retry;

		spte_set = true;
	}

	rcu_read_unlock();
	return spte_set;
}

/*
 * Clear the dirty status of all the SPTEs mapping GFNs in the memslot. If
 * AD bits are enabled, this will involve clearing the dirty bit on each SPTE.
 * If AD bits are not enabled, this will require clearing the writable bit on
 * each SPTE. Returns true if an SPTE has been changed and the TLBs need to
 * be flushed.
 */
bool kvm_tdp_mmu_clear_dirty_slot(struct kvm *kvm,
				  const struct kvm_memory_slot *slot)
{
	struct kvm_mmu_page *root;
	bool spte_set = false;

	lockdep_assert_held_read(&kvm->mmu_lock);

	for_each_valid_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, true)
		spte_set |= clear_dirty_gfn_range(kvm, root, slot->base_gfn,
				slot->base_gfn + slot->npages);

	return spte_set;
}

/*
 * Clears the dirty status of all the 4k SPTEs mapping GFNs for which a bit is
 * set in mask, starting at gfn. The given memslot is expected to contain all
 * the GFNs represented by set bits in the mask. If AD bits are enabled,
 * clearing the dirty status will involve clearing the dirty bit on each SPTE
 * or, if AD bits are not enabled, clearing the writable bit on each SPTE.
 */
static void clear_dirty_pt_masked(struct kvm *kvm, struct kvm_mmu_page *root,
				  gfn_t gfn, unsigned long mask, bool wrprot)
{
	struct tdp_iter iter;
	u64 new_spte;

	rcu_read_lock();

	tdp_root_for_each_leaf_pte(iter, root, gfn + __ffs(mask),
				    gfn + BITS_PER_LONG) {
		if (!mask)
			break;

		if (iter.level > PG_LEVEL_4K ||
		    !(mask & (1UL << (iter.gfn - gfn))))
			continue;

		mask &= ~(1UL << (iter.gfn - gfn));

		if (wrprot || spte_ad_need_write_protect(iter.old_spte)) {
			if (is_writable_pte(iter.old_spte))
				new_spte = iter.old_spte & ~PT_WRITABLE_MASK;
			else
				continue;
		} else {
			if (iter.old_spte & shadow_dirty_mask)
				new_spte = iter.old_spte & ~shadow_dirty_mask;
			else
				continue;
		}

		tdp_mmu_set_spte_no_dirty_log(kvm, &iter, new_spte);
	}

	rcu_read_unlock();
}

/*
 * Clears the dirty status of all the 4k SPTEs mapping GFNs for which a bit is
 * set in mask, starting at gfn. The given memslot is expected to contain all
 * the GFNs represented by set bits in the mask. If AD bits are enabled,
 * clearing the dirty status will involve clearing the dirty bit on each SPTE
 * or, if AD bits are not enabled, clearing the writable bit on each SPTE.
 */
void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
				       struct kvm_memory_slot *slot,
				       gfn_t gfn, unsigned long mask,
				       bool wrprot)
{
	struct kvm_mmu_page *root;

	lockdep_assert_held_write(&kvm->mmu_lock);
	for_each_tdp_mmu_root(kvm, root, slot->as_id)
		clear_dirty_pt_masked(kvm, root, gfn, mask, wrprot);
}

/*
 * Clear leaf entries which could be replaced by large mappings, for
 * GFNs within the slot.
 */
static void zap_collapsible_spte_range(struct kvm *kvm,
				       struct kvm_mmu_page *root,
				       const struct kvm_memory_slot *slot)
{
	gfn_t start = slot->base_gfn;
	gfn_t end = start + slot->npages;
	struct tdp_iter iter;
	kvm_pfn_t pfn;

	rcu_read_lock();

	tdp_root_for_each_pte(iter, root, start, end) {
retry:
		if (tdp_mmu_iter_cond_resched(kvm, &iter, false, true))
			continue;

		if (!is_shadow_present_pte(iter.old_spte) ||
		    !is_last_spte(iter.old_spte, iter.level))
			continue;

		pfn = spte_to_pfn(iter.old_spte);
		if (kvm_is_reserved_pfn(pfn) ||
		    iter.level >= kvm_mmu_max_mapping_level(kvm, slot, iter.gfn,
							    pfn, PG_LEVEL_NUM))
			continue;

		/* Note, a successful atomic zap also does a remote TLB flush. */
		if (tdp_mmu_zap_spte_atomic(kvm, &iter))
			goto retry;
	}

	rcu_read_unlock();
}

/*
 * Clear non-leaf entries (and free associated page tables) which could
 * be replaced by large mappings, for GFNs within the slot.
 */
void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
				       const struct kvm_memory_slot *slot)
{
	struct kvm_mmu_page *root;

	lockdep_assert_held_read(&kvm->mmu_lock);

	for_each_valid_tdp_mmu_root_yield_safe(kvm, root, slot->as_id, true)
		zap_collapsible_spte_range(kvm, root, slot);
}

/*
 * Removes write access on the last level SPTE mapping this GFN and unsets the
 * MMU-writable bit to ensure future writes continue to be intercepted.
 * Returns true if an SPTE was set and a TLB flush is needed.
 */
static bool write_protect_gfn(struct kvm *kvm, struct kvm_mmu_page *root,
			      gfn_t gfn, int min_level)
{
	struct tdp_iter iter;
	u64 new_spte;
	bool spte_set = false;

	BUG_ON(min_level > KVM_MAX_HUGEPAGE_LEVEL);

	rcu_read_lock();

	for_each_tdp_pte_min_level(iter, root, min_level, gfn, gfn + 1) {
		if (!is_shadow_present_pte(iter.old_spte) ||
		    !is_last_spte(iter.old_spte, iter.level))
			continue;

		new_spte = iter.old_spte &
			~(PT_WRITABLE_MASK | shadow_mmu_writable_mask);

		if (new_spte == iter.old_spte)
			break;

		tdp_mmu_set_spte(kvm, &iter, new_spte);
		spte_set = true;
	}

	rcu_read_unlock();

	return spte_set;
}

/*
 * Removes write access on the last level SPTE mapping this GFN and unsets the
 * MMU-writable bit to ensure future writes continue to be intercepted.
 * Returns true if an SPTE was set and a TLB flush is needed.
 */
bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
				   struct kvm_memory_slot *slot, gfn_t gfn,
				   int min_level)
{
	struct kvm_mmu_page *root;
	bool spte_set = false;

	lockdep_assert_held_write(&kvm->mmu_lock);
	for_each_tdp_mmu_root(kvm, root, slot->as_id)
		spte_set |= write_protect_gfn(kvm, root, gfn, min_level);

	return spte_set;
}

/*
 * Return the level of the lowest level SPTE added to sptes.
 * That SPTE may be non-present.
 *
 * Must be called between kvm_tdp_mmu_walk_lockless_{begin,end}.
 */
int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
			 int *root_level)
{
	struct tdp_iter iter;
	struct kvm_mmu *mmu = vcpu->arch.mmu;
	gfn_t gfn = addr >> PAGE_SHIFT;
	int leaf = -1;

	*root_level = vcpu->arch.mmu->shadow_root_level;

	tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) {
		leaf = iter.level;
		sptes[leaf] = iter.old_spte;
	}

	return leaf;
}

/*
 * Returns the last level spte pointer of the shadow page walk for the given
 * gpa, and sets *spte to the spte value. This spte may be non-preset. If no
 * walk could be performed, returns NULL and *spte does not contain valid data.
 *
 * Contract:
 *  - Must be called between kvm_tdp_mmu_walk_lockless_{begin,end}.
 *  - The returned sptep must not be used after kvm_tdp_mmu_walk_lockless_end.
 *
 * WARNING: This function is only intended to be called during fast_page_fault.
 */
u64 *kvm_tdp_mmu_fast_pf_get_last_sptep(struct kvm_vcpu *vcpu, u64 addr,
					u64 *spte)
{
	struct tdp_iter iter;
	struct kvm_mmu *mmu = vcpu->arch.mmu;
	gfn_t gfn = addr >> PAGE_SHIFT;
	tdp_ptep_t sptep = NULL;

	tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) {
		*spte = iter.old_spte;
		sptep = iter.sptep;
	}

	/*
	 * Perform the rcu_dereference to get the raw spte pointer value since
	 * we are passing it up to fast_page_fault, which is shared with the
	 * legacy MMU and thus does not retain the TDP MMU-specific __rcu
	 * annotation.
	 *
	 * This is safe since fast_page_fault obeys the contracts of this
	 * function as well as all TDP MMU contracts around modifying SPTEs
	 * outside of mmu_lock.
	 */
	return rcu_dereference(sptep);
}