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 = false; 30 iter->yielded_gfn = iter->next_last_level_gfn; 31 iter->level = iter->root_level; 32 33 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level); 34 tdp_iter_refresh_sptep(iter); 35 36 iter->valid = true; 37 } 38 39 /* 40 * Sets a TDP iterator to walk a pre-order traversal of the paging structure 41 * rooted at root_pt, starting with the walk to translate next_last_level_gfn. 42 */ 43 void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level, 44 int min_level, gfn_t next_last_level_gfn) 45 { 46 WARN_ON(root_level < 1); 47 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); 48 49 iter->next_last_level_gfn = next_last_level_gfn; 50 iter->root_level = root_level; 51 iter->min_level = min_level; 52 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root_pt; 53 iter->as_id = kvm_mmu_page_as_id(sptep_to_sp(root_pt)); 54 55 tdp_iter_restart(iter); 56 } 57 58 /* 59 * Given an SPTE and its level, returns a pointer containing the host virtual 60 * address of the child page table referenced by the SPTE. Returns null if 61 * there is no such entry. 62 */ 63 tdp_ptep_t spte_to_child_pt(u64 spte, int level) 64 { 65 /* 66 * There's no child entry if this entry isn't present or is a 67 * last-level entry. 68 */ 69 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) 70 return NULL; 71 72 return (tdp_ptep_t)__va(spte_to_pfn(spte) << PAGE_SHIFT); 73 } 74 75 /* 76 * Steps down one level in the paging structure towards the goal GFN. Returns 77 * true if the iterator was able to step down a level, false otherwise. 78 */ 79 static bool try_step_down(struct tdp_iter *iter) 80 { 81 tdp_ptep_t child_pt; 82 83 if (iter->level == iter->min_level) 84 return false; 85 86 /* 87 * Reread the SPTE before stepping down to avoid traversing into page 88 * tables that are no longer linked from this entry. 89 */ 90 iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); 91 92 child_pt = spte_to_child_pt(iter->old_spte, iter->level); 93 if (!child_pt) 94 return false; 95 96 iter->level--; 97 iter->pt_path[iter->level - 1] = child_pt; 98 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level); 99 tdp_iter_refresh_sptep(iter); 100 101 return true; 102 } 103 104 /* 105 * Steps to the next entry in the current page table, at the current page table 106 * level. The next entry could point to a page backing guest memory or another 107 * page table, or it could be non-present. Returns true if the iterator was 108 * able to step to the next entry in the page table, false if the iterator was 109 * already at the end of the current page table. 110 */ 111 static bool try_step_side(struct tdp_iter *iter) 112 { 113 /* 114 * Check if the iterator is already at the end of the current page 115 * table. 116 */ 117 if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) == 118 (PT64_ENT_PER_PAGE - 1)) 119 return false; 120 121 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); 122 iter->next_last_level_gfn = iter->gfn; 123 iter->sptep++; 124 iter->old_spte = READ_ONCE(*rcu_dereference(iter->sptep)); 125 126 return true; 127 } 128 129 /* 130 * Tries to traverse back up a level in the paging structure so that the walk 131 * can continue from the next entry in the parent page table. Returns true on a 132 * successful step up, false if already in the root page. 133 */ 134 static bool try_step_up(struct tdp_iter *iter) 135 { 136 if (iter->level == iter->root_level) 137 return false; 138 139 iter->level++; 140 iter->gfn = round_gfn_for_level(iter->gfn, iter->level); 141 tdp_iter_refresh_sptep(iter); 142 143 return true; 144 } 145 146 /* 147 * Step to the next SPTE in a pre-order traversal of the paging structure. 148 * To get to the next SPTE, the iterator either steps down towards the goal 149 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a 150 * highter GFN. 151 * 152 * The basic algorithm is as follows: 153 * 1. If the current SPTE is a non-last-level SPTE, step down into the page 154 * table it points to. 155 * 2. If the iterator cannot step down, it will try to step to the next SPTE 156 * in the current page of the paging structure. 157 * 3. If the iterator cannot step to the next entry in the current page, it will 158 * try to step up to the parent paging structure page. In this case, that 159 * SPTE will have already been visited, and so the iterator must also step 160 * to the side again. 161 */ 162 void tdp_iter_next(struct tdp_iter *iter) 163 { 164 if (iter->yielded) { 165 tdp_iter_restart(iter); 166 return; 167 } 168 169 if (try_step_down(iter)) 170 return; 171 172 do { 173 if (try_step_side(iter)) 174 return; 175 } while (try_step_up(iter)); 176 iter->valid = false; 177 } 178 179