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 goal_gfn.
26 */
tdp_iter_start(struct tdp_iter * iter,u64 * root_pt,int root_level,int min_level,gfn_t goal_gfn)27 void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,
28 int min_level, gfn_t goal_gfn)
29 {
30 WARN_ON(root_level < 1);
31 WARN_ON(root_level > PT64_ROOT_MAX_LEVEL);
32
33 iter->goal_gfn = goal_gfn;
34 iter->root_level = root_level;
35 iter->min_level = min_level;
36 iter->level = root_level;
37 iter->pt_path[iter->level - 1] = root_pt;
38
39 iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level);
40 tdp_iter_refresh_sptep(iter);
41
42 iter->valid = true;
43 }
44
45 /*
46 * Given an SPTE and its level, returns a pointer containing the host virtual
47 * address of the child page table referenced by the SPTE. Returns null if
48 * there is no such entry.
49 */
spte_to_child_pt(u64 spte,int level)50 u64 *spte_to_child_pt(u64 spte, int level)
51 {
52 /*
53 * There's no child entry if this entry isn't present or is a
54 * last-level entry.
55 */
56 if (!is_shadow_present_pte(spte) || is_last_spte(spte, level))
57 return NULL;
58
59 return __va(spte_to_pfn(spte) << PAGE_SHIFT);
60 }
61
62 /*
63 * Steps down one level in the paging structure towards the goal GFN. Returns
64 * true if the iterator was able to step down a level, false otherwise.
65 */
try_step_down(struct tdp_iter * iter)66 static bool try_step_down(struct tdp_iter *iter)
67 {
68 u64 *child_pt;
69
70 if (iter->level == iter->min_level)
71 return false;
72
73 /*
74 * Reread the SPTE before stepping down to avoid traversing into page
75 * tables that are no longer linked from this entry.
76 */
77 iter->old_spte = READ_ONCE(*iter->sptep);
78
79 child_pt = spte_to_child_pt(iter->old_spte, iter->level);
80 if (!child_pt)
81 return false;
82
83 iter->level--;
84 iter->pt_path[iter->level - 1] = child_pt;
85 iter->gfn = round_gfn_for_level(iter->goal_gfn, iter->level);
86 tdp_iter_refresh_sptep(iter);
87
88 return true;
89 }
90
91 /*
92 * Steps to the next entry in the current page table, at the current page table
93 * level. The next entry could point to a page backing guest memory or another
94 * page table, or it could be non-present. Returns true if the iterator was
95 * able to step to the next entry in the page table, false if the iterator was
96 * already at the end of the current page table.
97 */
try_step_side(struct tdp_iter * iter)98 static bool try_step_side(struct tdp_iter *iter)
99 {
100 /*
101 * Check if the iterator is already at the end of the current page
102 * table.
103 */
104 if (SHADOW_PT_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
105 (PT64_ENT_PER_PAGE - 1))
106 return false;
107
108 iter->gfn += KVM_PAGES_PER_HPAGE(iter->level);
109 iter->goal_gfn = iter->gfn;
110 iter->sptep++;
111 iter->old_spte = READ_ONCE(*iter->sptep);
112
113 return true;
114 }
115
116 /*
117 * Tries to traverse back up a level in the paging structure so that the walk
118 * can continue from the next entry in the parent page table. Returns true on a
119 * successful step up, false if already in the root page.
120 */
try_step_up(struct tdp_iter * iter)121 static bool try_step_up(struct tdp_iter *iter)
122 {
123 if (iter->level == iter->root_level)
124 return false;
125
126 iter->level++;
127 iter->gfn = round_gfn_for_level(iter->gfn, iter->level);
128 tdp_iter_refresh_sptep(iter);
129
130 return true;
131 }
132
133 /*
134 * Step to the next SPTE in a pre-order traversal of the paging structure.
135 * To get to the next SPTE, the iterator either steps down towards the goal
136 * GFN, if at a present, non-last-level SPTE, or over to a SPTE mapping a
137 * highter GFN.
138 *
139 * The basic algorithm is as follows:
140 * 1. If the current SPTE is a non-last-level SPTE, step down into the page
141 * table it points to.
142 * 2. If the iterator cannot step down, it will try to step to the next SPTE
143 * in the current page of the paging structure.
144 * 3. If the iterator cannot step to the next entry in the current page, it will
145 * try to step up to the parent paging structure page. In this case, that
146 * SPTE will have already been visited, and so the iterator must also step
147 * to the side again.
148 */
tdp_iter_next(struct tdp_iter * iter)149 void tdp_iter_next(struct tdp_iter *iter)
150 {
151 if (try_step_down(iter))
152 return;
153
154 do {
155 if (try_step_side(iter))
156 return;
157 } while (try_step_up(iter));
158 iter->valid = false;
159 }
160
161 /*
162 * Restart the walk over the paging structure from the root, starting from the
163 * highest gfn the iterator had previously reached. Assumes that the entire
164 * paging structure, except the root page, may have been completely torn down
165 * and rebuilt.
166 */
tdp_iter_refresh_walk(struct tdp_iter * iter)167 void tdp_iter_refresh_walk(struct tdp_iter *iter)
168 {
169 gfn_t goal_gfn = iter->goal_gfn;
170
171 if (iter->gfn > goal_gfn)
172 goal_gfn = iter->gfn;
173
174 tdp_iter_start(iter, iter->pt_path[iter->root_level - 1],
175 iter->root_level, iter->min_level, goal_gfn);
176 }
177
tdp_iter_root_pt(struct tdp_iter * iter)178 u64 *tdp_iter_root_pt(struct tdp_iter *iter)
179 {
180 return iter->pt_path[iter->root_level - 1];
181 }
182
183