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 */
tdp_iter_refresh_sptep(struct tdp_iter * iter)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 */
tdp_iter_restart(struct tdp_iter * iter)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 */
tdp_iter_start(struct tdp_iter * iter,struct kvm_mmu_page * root,int min_level,gfn_t next_last_level_gfn)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 */
spte_to_child_pt(u64 spte,int level)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 */
try_step_down(struct tdp_iter * iter)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 */
try_step_side(struct tdp_iter * iter)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 */
try_step_up(struct tdp_iter * iter)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 */
tdp_iter_next(struct tdp_iter * iter)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