1 // SPDX-License-Identifier: GPL-2.0 2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 3 4 #include "mmu_internal.h" 5 #include "tdp_iter.h" 6 #include "spte.h" 7 8 /* 9 * Recalculates the pointer to the SPTE for the current GFN and level and 10 * reread the SPTE. 11 */ 12 static void tdp_iter_refresh_sptep(struct tdp_iter *iter) 13 { 14 iter->sptep = iter->pt_path[iter->level - 1] + 15 SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level); 16 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 17 } 18 19 /* 20 * Return the TDP iterator to the root PT and allow it to continue its 21 * traversal over the paging structure from there. 22 */ 23 void tdp_iter_restart(struct tdp_iter *iter) 24 { 25 iter->yielded = false; 26 iter->yielded_gfn = iter->next_last_level_gfn; 27 iter->level = iter->root_level; 28 29 iter->gfn = gfn_round_for_level(iter->next_last_level_gfn, iter->level); 30 tdp_iter_refresh_sptep(iter); 31 32 iter->valid = true; 33 } 34 35 /* 36 * Sets a TDP iterator to walk a pre-order traversal of the paging structure 37 * rooted at root_pt, starting with the walk to translate next_last_level_gfn. 38 */ 39 void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root, 40 int min_level, gfn_t next_last_level_gfn) 41 { 42 int root_level = root->role.level; 43 44 WARN_ON(root_level < 1); 45 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); 46 47 iter->next_last_level_gfn = next_last_level_gfn; 48 iter->root_level = root_level; 49 iter->min_level = min_level; 50 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root->spt; 51 iter->as_id = kvm_mmu_page_as_id(root); 52 53 tdp_iter_restart(iter); 54 } 55 56 /* 57 * Given an SPTE and its level, returns a pointer containing the host virtual 58 * address of the child page table referenced by the SPTE. Returns null if 59 * there is no such entry. 60 */ 61 tdp_ptep_t spte_to_child_pt(u64 spte, int level) 62 { 63 /* 64 * There's no child entry if this entry isn't present or is a 65 * last-level entry. 66 */ 67 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) 68 return NULL; 69 70 return (tdp_ptep_t)__va(spte_to_pfn(spte) << PAGE_SHIFT); 71 } 72 73 /* 74 * Steps down one level in the paging structure towards the goal GFN. Returns 75 * true if the iterator was able to step down a level, false otherwise. 76 */ 77 static bool try_step_down(struct tdp_iter *iter) 78 { 79 tdp_ptep_t child_pt; 80 81 if (iter->level == iter->min_level) 82 return false; 83 84 /* 85 * Reread the SPTE before stepping down to avoid traversing into page 86 * tables that are no longer linked from this entry. 87 */ 88 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 89 90 child_pt = spte_to_child_pt(iter->old_spte, iter->level); 91 if (!child_pt) 92 return false; 93 94 iter->level--; 95 iter->pt_path[iter->level - 1] = child_pt; 96 iter->gfn = gfn_round_for_level(iter->next_last_level_gfn, iter->level); 97 tdp_iter_refresh_sptep(iter); 98 99 return true; 100 } 101 102 /* 103 * Steps to the next entry in the current page table, at the current page table 104 * level. The next entry could point to a page backing guest memory or another 105 * page table, or it could be non-present. Returns true if the iterator was 106 * able to step to the next entry in the page table, false if the iterator was 107 * already at the end of the current page table. 108 */ 109 static bool try_step_side(struct tdp_iter *iter) 110 { 111 /* 112 * Check if the iterator is already at the end of the current page 113 * table. 114 */ 115 if (SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level) == 116 (SPTE_ENT_PER_PAGE - 1)) 117 return false; 118 119 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); 120 iter->next_last_level_gfn = iter->gfn; 121 iter->sptep++; 122 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 123 124 return true; 125 } 126 127 /* 128 * Tries to traverse back up a level in the paging structure so that the walk 129 * can continue from the next entry in the parent page table. Returns true on a 130 * successful step up, false if already in the root page. 131 */ 132 static bool try_step_up(struct tdp_iter *iter) 133 { 134 if (iter->level == iter->root_level) 135 return false; 136 137 iter->level++; 138 iter->gfn = gfn_round_for_level(iter->gfn, iter->level); 139 tdp_iter_refresh_sptep(iter); 140 141 return true; 142 } 143 144 /* 145 * Step to the next SPTE in a pre-order traversal of the paging structure. 146 * To get to the next SPTE, the iterator either steps down towards the goal 147 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a 148 * highter GFN. 149 * 150 * The basic algorithm is as follows: 151 * 1. If the current SPTE is a non-last-level SPTE, step down into the page 152 * table it points to. 153 * 2. If the iterator cannot step down, it will try to step to the next SPTE 154 * in the current page of the paging structure. 155 * 3. If the iterator cannot step to the next entry in the current page, it will 156 * try to step up to the parent paging structure page. In this case, that 157 * SPTE will have already been visited, and so the iterator must also step 158 * to the side again. 159 */ 160 void tdp_iter_next(struct tdp_iter *iter) 161 { 162 if (iter->yielded) { 163 tdp_iter_restart(iter); 164 return; 165 } 166 167 if (try_step_down(iter)) 168 return; 169 170 do { 171 if (try_step_side(iter)) 172 return; 173 } while (try_step_up(iter)); 174 iter->valid = false; 175 } 176 177