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 | iter->gfn_bits) << 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, gfn_t gfn_bits) 41 { 42 if (WARN_ON_ONCE(!root || (root->role.level < 1) || 43 (root->role.level > PT64_ROOT_MAX_LEVEL) || 44 (gfn_bits && next_last_level_gfn >= gfn_bits))) { 45 iter->valid = false; 46 return; 47 } 48 49 iter->next_last_level_gfn = next_last_level_gfn; 50 iter->gfn_bits = gfn_bits; 51 iter->root_level = root->role.level; 52 iter->min_level = min_level; 53 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root->spt; 54 iter->as_id = kvm_mmu_page_as_id(root); 55 56 tdp_iter_restart(iter); 57 } 58 59 /* 60 * Given an SPTE and its level, returns a pointer containing the host virtual 61 * address of the child page table referenced by the SPTE. Returns null if 62 * there is no such entry. 63 */ 64 tdp_ptep_t spte_to_child_pt(u64 spte, int level) 65 { 66 /* 67 * There's no child entry if this entry isn't present or is a 68 * last-level entry. 69 */ 70 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) 71 return NULL; 72 73 return (tdp_ptep_t)__va(spte_to_pfn(spte) << PAGE_SHIFT); 74 } 75 76 /* 77 * Steps down one level in the paging structure towards the goal GFN. Returns 78 * true if the iterator was able to step down a level, false otherwise. 79 */ 80 static bool try_step_down(struct tdp_iter *iter) 81 { 82 tdp_ptep_t child_pt; 83 84 if (iter->level == iter->min_level) 85 return false; 86 87 /* 88 * Reread the SPTE before stepping down to avoid traversing into page 89 * tables that are no longer linked from this entry. 90 */ 91 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 92 93 child_pt = spte_to_child_pt(iter->old_spte, iter->level); 94 if (!child_pt) 95 return false; 96 97 iter->level--; 98 iter->pt_path[iter->level - 1] = child_pt; 99 iter->gfn = gfn_round_for_level(iter->next_last_level_gfn, iter->level); 100 tdp_iter_refresh_sptep(iter); 101 102 return true; 103 } 104 105 /* 106 * Steps to the next entry in the current page table, at the current page table 107 * level. The next entry could point to a page backing guest memory or another 108 * page table, or it could be non-present. Returns true if the iterator was 109 * able to step to the next entry in the page table, false if the iterator was 110 * already at the end of the current page table. 111 */ 112 static bool try_step_side(struct tdp_iter *iter) 113 { 114 /* 115 * Check if the iterator is already at the end of the current page 116 * table. 117 */ 118 if (SPTE_INDEX((iter->gfn | iter->gfn_bits) << PAGE_SHIFT, iter->level) == 119 (SPTE_ENT_PER_PAGE - 1)) 120 return false; 121 122 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); 123 iter->next_last_level_gfn = iter->gfn; 124 iter->sptep++; 125 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep); 126 127 return true; 128 } 129 130 /* 131 * Tries to traverse back up a level in the paging structure so that the walk 132 * can continue from the next entry in the parent page table. Returns true on a 133 * successful step up, false if already in the root page. 134 */ 135 static bool try_step_up(struct tdp_iter *iter) 136 { 137 if (iter->level == iter->root_level) 138 return false; 139 140 iter->level++; 141 iter->gfn = gfn_round_for_level(iter->gfn, iter->level); 142 tdp_iter_refresh_sptep(iter); 143 144 return true; 145 } 146 147 /* 148 * Step to the next SPTE in a pre-order traversal of the paging structure. 149 * To get to the next SPTE, the iterator either steps down towards the goal 150 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a 151 * higher GFN. 152 * 153 * The basic algorithm is as follows: 154 * 1. If the current SPTE is a non-last-level SPTE, step down into the page 155 * table it points to. 156 * 2. If the iterator cannot step down, it will try to step to the next SPTE 157 * in the current page of the paging structure. 158 * 3. If the iterator cannot step to the next entry in the current page, it will 159 * try to step up to the parent paging structure page. In this case, that 160 * SPTE will have already been visited, and so the iterator must also step 161 * to the side again. 162 */ 163 void tdp_iter_next(struct tdp_iter *iter) 164 { 165 if (iter->yielded) { 166 tdp_iter_restart(iter); 167 return; 168 } 169 170 if (try_step_down(iter)) 171 return; 172 173 do { 174 if (try_step_side(iter)) 175 return; 176 } while (try_step_up(iter)); 177 iter->valid = false; 178 } 179 180