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_gfn = iter->next_last_level_gfn;
30 iter->level = iter->root_level;
31
32 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level);
33 tdp_iter_refresh_sptep(iter);
34
35 iter->valid = true;
36 }
37
38 /*
39 * Sets a TDP iterator to walk a pre-order traversal of the paging structure
40 * rooted at root_pt, starting with the walk to translate next_last_level_gfn.
41 */
tdp_iter_start(struct tdp_iter * iter,u64 * root_pt,int root_level,int min_level,gfn_t next_last_level_gfn)42 void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,
43 int min_level, gfn_t next_last_level_gfn)
44 {
45 WARN_ON(root_level < 1);
46 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL);
47
48 iter->next_last_level_gfn = next_last_level_gfn;
49 iter->root_level = root_level;
50 iter->min_level = min_level;
51 iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root_pt;
52 iter->as_id = kvm_mmu_page_as_id(sptep_to_sp(root_pt));
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 */
spte_to_child_pt(u64 spte,int level)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 */
try_step_down(struct tdp_iter * iter)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 = READ_ONCE(*rcu_dereference(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 = round_gfn_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 */
try_step_side(struct tdp_iter * iter)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 (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
117 (PT64_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 = READ_ONCE(*rcu_dereference(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 */
try_step_up(struct tdp_iter * iter)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 = round_gfn_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 * highter 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 */
tdp_iter_next(struct tdp_iter * iter)161 void tdp_iter_next(struct tdp_iter *iter)
162 {
163 if (try_step_down(iter))
164 return;
165
166 do {
167 if (try_step_side(iter))
168 return;
169 } while (try_step_up(iter));
170 iter->valid = false;
171 }
172
173