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