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