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