1// SPDX-License-Identifier: GPL-2.0
2#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
3
4#include "mmu_internal.h"
5#include "tdp_iter.h"
6#include "spte.h"
7
8/*
9 * Recalculates the pointer to the SPTE for the current GFN and level and
10 * reread the SPTE.
11 */
12static void tdp_iter_refresh_sptep(struct tdp_iter *iter)
13{
14	iter->sptep = iter->pt_path[iter->level - 1] +
15		SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level);
16	iter->old_spte = kvm_tdp_mmu_read_spte(iter->sptep);
17}
18
19/*
20 * Return the TDP iterator to the root PT and allow it to continue its
21 * traversal over the paging structure from there.
22 */
23void tdp_iter_restart(struct tdp_iter *iter)
24{
25	iter->yielded = false;
26	iter->yielded_gfn = iter->next_last_level_gfn;
27	iter->level = iter->root_level;
28
29	iter->gfn = gfn_round_for_level(iter->next_last_level_gfn, iter->level);
30	tdp_iter_refresh_sptep(iter);
31
32	iter->valid = true;
33}
34
35/*
36 * Sets a TDP iterator to walk a pre-order traversal of the paging structure
37 * rooted at root_pt, starting with the walk to translate next_last_level_gfn.
38 */
39void tdp_iter_start(struct tdp_iter *iter, struct kvm_mmu_page *root,
40		    int min_level, gfn_t next_last_level_gfn)
41{
42	if (WARN_ON_ONCE(!root || (root->role.level < 1) ||
43			 (root->role.level > PT64_ROOT_MAX_LEVEL))) {
44		iter->valid = false;
45		return;
46	}
47
48	iter->next_last_level_gfn = next_last_level_gfn;
49	iter->root_level = root->role.level;
50	iter->min_level = min_level;
51	iter->pt_path[iter->root_level - 1] = (tdp_ptep_t)root->spt;
52	iter->as_id = kvm_mmu_page_as_id(root);
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 */
62tdp_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 */
78static 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 = kvm_tdp_mmu_read_spte(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 = gfn_round_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 */
110static 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 (SPTE_INDEX(iter->gfn << PAGE_SHIFT, iter->level) ==
117	    (SPTE_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 = kvm_tdp_mmu_read_spte(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 */
133static 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 = gfn_round_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 * higher 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 */
161void tdp_iter_next(struct tdp_iter *iter)
162{
163	if (iter->yielded) {
164		tdp_iter_restart(iter);
165		return;
166	}
167
168	if (try_step_down(iter))
169		return;
170
171	do {
172		if (try_step_side(iter))
173			return;
174	} while (try_step_up(iter));
175	iter->valid = false;
176}
177
178