tdp_iter.c

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