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(*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 * Sets a TDP iterator to walk a pre-order traversal of the paging structure 25 * rooted at root_pt, starting with the walk to translate goal_gfn. 26 */ 27 void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level, 28 int min_level, gfn_t goal_gfn) 29 { 30 WARN_ON(root_level < 1); 31 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL); 32 33 iter->goal_gfn = goal_gfn; 34 iter->root_level = root_level; 35 iter->min_level = min_level; 36 iter->level = root_level; 37 iter->pt_path[iter->level - 1] = root_pt; 38 39 iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level); 40 tdp_iter_refresh_sptep(iter); 41 42 iter->valid = true; 43 } 44 45 /* 46 * Given an SPTE and its level, returns a pointer containing the host virtual 47 * address of the child page table referenced by the SPTE. Returns null if 48 * there is no such entry. 49 */ 50 u64 *spte_to_child_pt(u64 spte, int level) 51 { 52 /* 53 * There's no child entry if this entry isn't present or is a 54 * last-level entry. 55 */ 56 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level)) 57 return NULL; 58 59 return __va(spte_to_pfn(spte) << PAGE_SHIFT); 60 } 61 62 /* 63 * Steps down one level in the paging structure towards the goal GFN. Returns 64 * true if the iterator was able to step down a level, false otherwise. 65 */ 66 static bool try_step_down(struct tdp_iter *iter) 67 { 68 u64 *child_pt; 69 70 if (iter->level == iter->min_level) 71 return false; 72 73 /* 74 * Reread the SPTE before stepping down to avoid traversing into page 75 * tables that are no longer linked from this entry. 76 */ 77 iter->old_spte = READ_ONCE(*iter->sptep); 78 79 child_pt = spte_to_child_pt(iter->old_spte, iter->level); 80 if (!child_pt) 81 return false; 82 83 iter->level--; 84 iter->pt_path[iter->level - 1] = child_pt; 85 iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level); 86 tdp_iter_refresh_sptep(iter); 87 88 return true; 89 } 90 91 /* 92 * Steps to the next entry in the current page table, at the current page table 93 * level. The next entry could point to a page backing guest memory or another 94 * page table, or it could be non-present. Returns true if the iterator was 95 * able to step to the next entry in the page table, false if the iterator was 96 * already at the end of the current page table. 97 */ 98 static bool try_step_side(struct tdp_iter *iter) 99 { 100 /* 101 * Check if the iterator is already at the end of the current page 102 * table. 103 */ 104 if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) == 105 (PT64_ENT_PER_PAGE - 1)) 106 return false; 107 108 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level); 109 iter->goal_gfn = iter->gfn; 110 iter->sptep++; 111 iter->old_spte = READ_ONCE(*iter->sptep); 112 113 return true; 114 } 115 116 /* 117 * Tries to traverse back up a level in the paging structure so that the walk 118 * can continue from the next entry in the parent page table. Returns true on a 119 * successful step up, false if already in the root page. 120 */ 121 static bool try_step_up(struct tdp_iter *iter) 122 { 123 if (iter->level == iter->root_level) 124 return false; 125 126 iter->level++; 127 iter->gfn = round_gfn_for_level(iter->gfn, iter->level); 128 tdp_iter_refresh_sptep(iter); 129 130 return true; 131 } 132 133 /* 134 * Step to the next SPTE in a pre-order traversal of the paging structure. 135 * To get to the next SPTE, the iterator either steps down towards the goal 136 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a 137 * highter GFN. 138 * 139 * The basic algorithm is as follows: 140 * 1. If the current SPTE is a non-last-level SPTE, step down into the page 141 * table it points to. 142 * 2. If the iterator cannot step down, it will try to step to the next SPTE 143 * in the current page of the paging structure. 144 * 3. If the iterator cannot step to the next entry in the current page, it will 145 * try to step up to the parent paging structure page. In this case, that 146 * SPTE will have already been visited, and so the iterator must also step 147 * to the side again. 148 */ 149 void tdp_iter_next(struct tdp_iter *iter) 150 { 151 if (try_step_down(iter)) 152 return; 153 154 do { 155 if (try_step_side(iter)) 156 return; 157 } while (try_step_up(iter)); 158 iter->valid = false; 159 } 160 161 /* 162 * Restart the walk over the paging structure from the root, starting from the 163 * highest gfn the iterator had previously reached. Assumes that the entire 164 * paging structure, except the root page, may have been completely torn down 165 * and rebuilt. 166 */ 167 void tdp_iter_refresh_walk(struct tdp_iter *iter) 168 { 169 gfn_t goal_gfn = iter->goal_gfn; 170 171 if (iter->gfn > goal_gfn) 172 goal_gfn = iter->gfn; 173 174 tdp_iter_start(iter, iter->pt_path[iter->root_level - 1], 175 iter->root_level, iter->min_level, goal_gfn); 176 } 177 178 u64 *tdp_iter_root_pt(struct tdp_iter *iter) 179 { 180 return iter->pt_path[iter->root_level - 1]; 181 } 182 183