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