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(*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 * Sets a TDP iterator to walk a pre-order traversal of the paging structure
25 * rooted at root_pt, starting with the walk to translate next_last_level_gfn.
26 */
tdp_iter_start(struct tdp_iter * iter,u64 * root_pt,int root_level,int min_level,gfn_t next_last_level_gfn)27 void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,
28 int min_level, gfn_t next_last_level_gfn)
29 {
30 WARN_ON(root_level < 1);
31 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL);
32
33 iter->next_last_level_gfn = next_last_level_gfn;
34 iter->yielded_gfn = iter->next_last_level_gfn;
35 iter->root_level = root_level;
36 iter->min_level = min_level;
37 iter->level = root_level;
38 iter->pt_path[iter->level - 1] = root_pt;
39
40 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level);
41 tdp_iter_refresh_sptep(iter);
42
43 iter->valid = true;
44 }
45
46 /*
47 * Given an SPTE and its level, returns a pointer containing the host virtual
48 * address of the child page table referenced by the SPTE. Returns null if
49 * there is no such entry.
50 */
spte_to_child_pt(u64 spte,int level)51 u64 *spte_to_child_pt(u64 spte, int level)
52 {
53 /*
54 * There's no child entry if this entry isn't present or is a
55 * last-level entry.
56 */
57 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level))
58 return NULL;
59
60 return __va(spte_to_pfn(spte) << PAGE_SHIFT);
61 }
62
63 /*
64 * Steps down one level in the paging structure towards the goal GFN. Returns
65 * true if the iterator was able to step down a level, false otherwise.
66 */
try_step_down(struct tdp_iter * iter)67 static bool try_step_down(struct tdp_iter *iter)
68 {
69 u64 *child_pt;
70
71 if (iter->level == iter->min_level)
72 return false;
73
74 /*
75 * Reread the SPTE before stepping down to avoid traversing into page
76 * tables that are no longer linked from this entry.
77 */
78 iter->old_spte = READ_ONCE(*iter->sptep);
79
80 child_pt = spte_to_child_pt(iter->old_spte, iter->level);
81 if (!child_pt)
82 return false;
83
84 iter->level--;
85 iter->pt_path[iter->level - 1] = child_pt;
86 iter->gfn = round_gfn_for_level(iter->next_last_level_gfn, iter->level);
87 tdp_iter_refresh_sptep(iter);
88
89 return true;
90 }
91
92 /*
93 * Steps to the next entry in the current page table, at the current page table
94 * level. The next entry could point to a page backing guest memory or another
95 * page table, or it could be non-present. Returns true if the iterator was
96 * able to step to the next entry in the page table, false if the iterator was
97 * already at the end of the current page table.
98 */
try_step_side(struct tdp_iter * iter)99 static bool try_step_side(struct tdp_iter *iter)
100 {
101 /*
102 * Check if the iterator is already at the end of the current page
103 * table.
104 */
105 if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
106 (PT64_ENT_PER_PAGE - 1))
107 return false;
108
109 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level);
110 iter->next_last_level_gfn = iter->gfn;
111 iter->sptep++;
112 iter->old_spte = READ_ONCE(*iter->sptep);
113
114 return true;
115 }
116
117 /*
118 * Tries to traverse back up a level in the paging structure so that the walk
119 * can continue from the next entry in the parent page table. Returns true on a
120 * successful step up, false if already in the root page.
121 */
try_step_up(struct tdp_iter * iter)122 static bool try_step_up(struct tdp_iter *iter)
123 {
124 if (iter->level == iter->root_level)
125 return false;
126
127 iter->level++;
128 iter->gfn = round_gfn_for_level(iter->gfn, iter->level);
129 tdp_iter_refresh_sptep(iter);
130
131 return true;
132 }
133
134 /*
135 * Step to the next SPTE in a pre-order traversal of the paging structure.
136 * To get to the next SPTE, the iterator either steps down towards the goal
137 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a
138 * highter GFN.
139 *
140 * The basic algorithm is as follows:
141 * 1. If the current SPTE is a non-last-level SPTE, step down into the page
142 * table it points to.
143 * 2. If the iterator cannot step down, it will try to step to the next SPTE
144 * in the current page of the paging structure.
145 * 3. If the iterator cannot step to the next entry in the current page, it will
146 * try to step up to the parent paging structure page. In this case, that
147 * SPTE will have already been visited, and so the iterator must also step
148 * to the side again.
149 */
tdp_iter_next(struct tdp_iter * iter)150 void tdp_iter_next(struct tdp_iter *iter)
151 {
152 if (try_step_down(iter))
153 return;
154
155 do {
156 if (try_step_side(iter))
157 return;
158 } while (try_step_up(iter));
159 iter->valid = false;
160 }
161
tdp_iter_root_pt(struct tdp_iter * iter)162 u64 *tdp_iter_root_pt(struct tdp_iter *iter)
163 {
164 return iter->pt_path[iter->root_level - 1];
165 }
166
167