1 // SPDX-License-Identifier: GPL-2.0 2 3 #include "mmu_internal.h" 4 #include "tdp_iter.h" 5 #include "spte.h" 6 7 /* 8 * Recalculates the pointer to the SPTE for the current GFN and level and 9 * reread the SPTE. 10 */ 11 static void tdp_iter_refresh_sptep(struct tdp_iter *iter) 12 { 13 iter->sptep = iter->pt_path[iter->level - 1] + 14 SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level); 15 iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); 16 } 17 18 static gfn_t round_gfn_for_level(gfn_t gfn, int level) 19 { 20 return gfn & -KVM_PAGES_PER_HPAGE(level); 21 } 22 23 /* 24 * Return the TDP iterator to the root PT and allow it to continue its 25 * traversal over the paging structure from there. 26 */ 27 void tdp_iter_restart(struct tdp_iter *iter) 28 { 29 iter->yielded_gfn = iter->next_last_level_gfn; 30 iter->level = iter->root_level; 31 32 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level); 33 tdp_iter_refresh_sptep(iter); 34 35 iter->valid = true; 36 } 37 38 /* 39 * Sets a TDP iterator to walk a pre-order traversal of the paging structure 40 * rooted at root_pt, starting with the walk to translate next_last_level_gfn. 41 */ 42 void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level, 43 int min_level, gfn_t next_last_level_gfn) 44 { 45 WARN_ON(root_level < 1); 46 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); 47 48 iter->next_last_level_gfn = next_last_level_gfn; 49 iter->root_level = root_level; 50 iter->min_level = min_level; 51 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root_pt; 52 iter->as_id = kvm_mmu_page_as_id(sptep_to_sp(root_pt)); 53 54 tdp_iter_restart(iter); 55 } 56 57 /* 58 * Given an SPTE and its level, returns a pointer containing the host virtual 59 * address of the child page table referenced by the SPTE. Returns null if 60 * there is no such entry. 61 */ 62 tdp_ptep_t spte_to_child_pt(u64 spte, int level) 63 { 64 /* 65 * There's no child entry if this entry isn't present or is a 66 * last-level entry. 67 */ 68 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) 69 return NULL; 70 71 return (tdp_ptep_t)__va(spte_to_pfn(spte) << PAGE_SHIFT); 72 } 73 74 /* 75 * Steps down one level in the paging structure towards the goal GFN. Returns 76 * true if the iterator was able to step down a level, false otherwise. 77 */ 78 static bool try_step_down(struct tdp_iter *iter) 79 { 80 tdp_ptep_t child_pt; 81 82 if (iter->level == iter->min_level) 83 return false; 84 85 /* 86 * Reread the SPTE before stepping down to avoid traversing into page 87 * tables that are no longer linked from this entry. 88 */ 89 iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); 90 91 child_pt = spte_to_child_pt(iter->old_spte, iter->level); 92 if (!child_pt) 93 return false; 94 95 iter->level--; 96 iter->pt_path[iter->level - 1] = child_pt; 97 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level); 98 tdp_iter_refresh_sptep(iter); 99 100 return true; 101 } 102 103 /* 104 * Steps to the next entry in the current page table, at the current page table 105 * level. The next entry could point to a page backing guest memory or another 106 * page table, or it could be non-present. Returns true if the iterator was 107 * able to step to the next entry in the page table, false if the iterator was 108 * already at the end of the current page table. 109 */ 110 static bool try_step_side(struct tdp_iter *iter) 111 { 112 /* 113 * Check if the iterator is already at the end of the current page 114 * table. 115 */ 116 if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) == 117 (PT64_ENT_PER_PAGE - 1)) 118 return false; 119 120 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); 121 iter->next_last_level_gfn = iter->gfn; 122 iter->sptep++; 123 iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); 124 125 return true; 126 } 127 128 /* 129 * Tries to traverse back up a level in the paging structure so that the walk 130 * can continue from the next entry in the parent page table. Returns true on a 131 * successful step up, false if already in the root page. 132 */ 133 static bool try_step_up(struct tdp_iter *iter) 134 { 135 if (iter->level == iter->root_level) 136 return false; 137 138 iter->level++; 139 iter->gfn = round_gfn_for_level(iter->gfn, iter->level); 140 tdp_iter_refresh_sptep(iter); 141 142 return true; 143 } 144 145 /* 146 * Step to the next SPTE in a pre-order traversal of the paging structure. 147 * To get to the next SPTE, the iterator either steps down towards the goal 148 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a 149 * highter GFN. 150 * 151 * The basic algorithm is as follows: 152 * 1. If the current SPTE is a non-last-level SPTE, step down into the page 153 * table it points to. 154 * 2. If the iterator cannot step down, it will try to step to the next SPTE 155 * in the current page of the paging structure. 156 * 3. If the iterator cannot step to the next entry in the current page, it will 157 * try to step up to the parent paging structure page. In this case, that 158 * SPTE will have already been visited, and so the iterator must also step 159 * to the side again. 160 */ 161 void tdp_iter_next(struct tdp_iter *iter) 162 { 163 if (try_step_down(iter)) 164 return; 165 166 do { 167 if (try_step_side(iter)) 168 return; 169 } while (try_step_up(iter)); 170 iter->valid = false; 171 } 172 173