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 */
tdp_iter_refresh_sptep(struct tdp_iter * iter)11 static void tdp_iter_refresh_sptep(struct tdp_iter *iter)
12 {
13 iter->sptep = iter->pt_path[iter->level - 1] +
14 SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level);
15 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
16 }
17
round_gfn_for_level(gfn_t gfn,int level)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 * Return the TDP iterator to the root PT and allow it to continue its
25 * traversal over the paging structure from there.
26 */
tdp_iter_restart(struct tdp_iter * iter)27 void tdp_iter_restart(struct tdp_iter *iter)
28 {
29 iter->yielded = false;
30 iter->yielded_gfn = iter->next_last_level_gfn;
31 iter->level = iter->root_level;
32
33 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level);
34 tdp_iter_refresh_sptep(iter);
35
36 iter->valid = true;
37 }
38
39 /*
40 * Sets a TDP iterator to walk a pre-order traversal of the paging structure
41 * rooted at root_pt, starting with the walk to translate next_last_level_gfn.
42 */
tdp_iter_start(struct tdp_iter * iter,struct kvm_mmu_page * root,int min_level,gfn_t next_last_level_gfn)43 void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root,
44 int min_level, gfn_t next_last_level_gfn)
45 {
46 int root_level = root->role.level;
47
48 WARN_ON(root_level < 1);
49 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL);
50
51 iter->next_last_level_gfn = next_last_level_gfn;
52 iter->root_level = root_level;
53 iter->min_level = min_level;
54 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root->spt;
55 iter->as_id = kvm_mmu_page_as_id(root);
56
57 tdp_iter_restart(iter);
58 }
59
60 /*
61 * Given an SPTE and its level, returns a pointer containing the host virtual
62 * address of the child page table referenced by the SPTE. Returns null if
63 * there is no such entry.
64 */
spte_to_child_pt(u64 spte,int level)65 tdp_ptep_t spte_to_child_pt(u64 spte, int level)
66 {
67 /*
68 * There's no child entry if this entry isn't present or is a
69 * last-level entry.
70 */
71 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level))
72 return NULL;
73
74 return (tdp_ptep_t)__va(spte_to_pfn(spte) << PAGE_SHIFT);
75 }
76
77 /*
78 * Steps down one level in the paging structure towards the goal GFN. Returns
79 * true if the iterator was able to step down a level, false otherwise.
80 */
try_step_down(struct tdp_iter * iter)81 static bool try_step_down(struct tdp_iter *iter)
82 {
83 tdp_ptep_t child_pt;
84
85 if (iter->level == iter->min_level)
86 return false;
87
88 /*
89 * Reread the SPTE before stepping down to avoid traversing into page
90 * tables that are no longer linked from this entry.
91 */
92 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
93
94 child_pt = spte_to_child_pt(iter->old_spte, iter->level);
95 if (!child_pt)
96 return false;
97
98 iter->level--;
99 iter->pt_path[iter->level - 1] = child_pt;
100 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level);
101 tdp_iter_refresh_sptep(iter);
102
103 return true;
104 }
105
106 /*
107 * Steps to the next entry in the current page table, at the current page table
108 * level. The next entry could point to a page backing guest memory or another
109 * page table, or it could be non-present. Returns true if the iterator was
110 * able to step to the next entry in the page table, false if the iterator was
111 * already at the end of the current page table.
112 */
try_step_side(struct tdp_iter * iter)113 static bool try_step_side(struct tdp_iter *iter)
114 {
115 /*
116 * Check if the iterator is already at the end of the current page
117 * table.
118 */
119 if (SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
120 (SPTE_ENT_PER_PAGE - 1))
121 return false;
122
123 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level);
124 iter->next_last_level_gfn = iter->gfn;
125 iter->sptep++;
126 iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
127
128 return true;
129 }
130
131 /*
132 * Tries to traverse back up a level in the paging structure so that the walk
133 * can continue from the next entry in the parent page table. Returns true on a
134 * successful step up, false if already in the root page.
135 */
try_step_up(struct tdp_iter * iter)136 static bool try_step_up(struct tdp_iter *iter)
137 {
138 if (iter->level == iter->root_level)
139 return false;
140
141 iter->level++;
142 iter->gfn = round_gfn_for_level(iter->gfn, iter->level);
143 tdp_iter_refresh_sptep(iter);
144
145 return true;
146 }
147
148 /*
149 * Step to the next SPTE in a pre-order traversal of the paging structure.
150 * To get to the next SPTE, the iterator either steps down towards the goal
151 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a
152 * highter GFN.
153 *
154 * The basic algorithm is as follows:
155 * 1. If the current SPTE is a non-last-level SPTE, step down into the page
156 * table it points to.
157 * 2. If the iterator cannot step down, it will try to step to the next SPTE
158 * in the current page of the paging structure.
159 * 3. If the iterator cannot step to the next entry in the current page, it will
160 * try to step up to the parent paging structure page. In this case, that
161 * SPTE will have already been visited, and so the iterator must also step
162 * to the side again.
163 */
tdp_iter_next(struct tdp_iter * iter)164 void tdp_iter_next(struct tdp_iter *iter)
165 {
166 if (iter->yielded) {
167 tdp_iter_restart(iter);
168 return;
169 }
170
171 if (try_step_down(iter))
172 return;
173
174 do {
175 if (try_step_side(iter))
176 return;
177 } while (try_step_up(iter));
178 iter->valid = false;
179 }
180
181