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 SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level); 15 iter->old_spte = kvm_tdp_mmu_read_spte(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, struct kvm_mmu_page *root, 44 int min_level, gfn_t next_last_level_gfn) 45 { 46 int root_level = root->role.level; 47 48 WARN_ON(root_level < 1); 49 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); 50 51 iter->next_last_level_gfn = next_last_level_gfn; 52 iter->root_level = root_level; 53 iter->min_level = min_level; 54 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root->spt; 55 iter->as_id = kvm_mmu_page_as_id(root); 56 57 tdp_iter_restart(iter); 58 } 59 60 /* 61 * Given an SPTE and its level, returns a pointer containing the host virtual 62 * address of the child page table referenced by the SPTE. Returns null if 63 * there is no such entry. 64 */ 65 tdp_ptep_t spte_to_child_pt(u64 spte, int level) 66 { 67 /* 68 * There's no child entry if this entry isn't present or is a 69 * last-level entry. 70 */ 71 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) 72 return NULL; 73 74 return (tdp_ptep_t)__va(spte_to_pfn(spte) << PAGE_SHIFT); 75 } 76 77 /* 78 * Steps down one level in the paging structure towards the goal GFN. Returns 79 * true if the iterator was able to step down a level, false otherwise. 80 */ 81 static bool try_step_down(struct tdp_iter *iter) 82 { 83 tdp_ptep_t child_pt; 84 85 if (iter->level == iter->min_level) 86 return false; 87 88 /* 89 * Reread the SPTE before stepping down to avoid traversing into page 90 * tables that are no longer linked from this entry. 91 */ 92 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 93 94 child_pt = spte_to_child_pt(iter->old_spte, iter->level); 95 if (!child_pt) 96 return false; 97 98 iter->level--; 99 iter->pt_path[iter->level - 1] = child_pt; 100 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level); 101 tdp_iter_refresh_sptep(iter); 102 103 return true; 104 } 105 106 /* 107 * Steps to the next entry in the current page table, at the current page table 108 * level. The next entry could point to a page backing guest memory or another 109 * page table, or it could be non-present. Returns true if the iterator was 110 * able to step to the next entry in the page table, false if the iterator was 111 * already at the end of the current page table. 112 */ 113 static bool try_step_side(struct tdp_iter *iter) 114 { 115 /* 116 * Check if the iterator is already at the end of the current page 117 * table. 118 */ 119 if (SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level) == 120 (SPTE_ENT_PER_PAGE - 1)) 121 return false; 122 123 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); 124 iter->next_last_level_gfn = iter->gfn; 125 iter->sptep++; 126 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 127 128 return true; 129 } 130 131 /* 132 * Tries to traverse back up a level in the paging structure so that the walk 133 * can continue from the next entry in the parent page table. Returns true on a 134 * successful step up, false if already in the root page. 135 */ 136 static bool try_step_up(struct tdp_iter *iter) 137 { 138 if (iter->level == iter->root_level) 139 return false; 140 141 iter->level++; 142 iter->gfn = round_gfn_for_level(iter->gfn, iter->level); 143 tdp_iter_refresh_sptep(iter); 144 145 return true; 146 } 147 148 /* 149 * Step to the next SPTE in a pre-order traversal of the paging structure. 150 * To get to the next SPTE, the iterator either steps down towards the goal 151 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a 152 * highter GFN. 153 * 154 * The basic algorithm is as follows: 155 * 1. If the current SPTE is a non-last-level SPTE, step down into the page 156 * table it points to. 157 * 2. If the iterator cannot step down, it will try to step to the next SPTE 158 * in the current page of the paging structure. 159 * 3. If the iterator cannot step to the next entry in the current page, it will 160 * try to step up to the parent paging structure page. In this case, that 161 * SPTE will have already been visited, and so the iterator must also step 162 * to the side again. 163 */ 164 void tdp_iter_next(struct tdp_iter *iter) 165 { 166 if (iter->yielded) { 167 tdp_iter_restart(iter); 168 return; 169 } 170 171 if (try_step_down(iter)) 172 return; 173 174 do { 175 if (try_step_side(iter)) 176 return; 177 } while (try_step_up(iter)); 178 iter->valid = false; 179 } 180 181