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KVM: x86: MMU: Consolidate BUG_ON checks for reverse-mapped sptes

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At some call sites of rmap_get_first() and rmap_get_next(), BUG_ON is
placed right after the call to detect unrelated sptes which must not be
found in the reverse-mapping list.

Move this check in rmap_get_first/next() so that all call sites, not
just the users of the for_each_rmap_spte() macro, will be checked the
same way.

One thing to keep in mind is that kvm_mmu_unlink_parents() also uses
rmap_get_first() to handle parent sptes.  The change will not break it
because parent sptes are present, at least until drop_parent_pte()
actually unlinks them, and not mmio-sptes.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Takuya Yoshikawa 2015-11-20 17:45:44 +09:00 committed by Paolo Bonzini
parent afd28fe1c9
commit 77fbbbd2f0
2 changed files with 19 additions and 11 deletions
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4
Documentation/virtual/kvm/mmu.txt
View File

@ -203,10 +203,10 @@ Shadow pages contain the following information:
page cannot be destroyed. See role.invalid.
parent_ptes:
The reverse mapping for the pte/ptes pointing at this page's spt. If
parent_ptes bit 0 is zero, only one spte points at this pages and
parent_ptes bit 0 is zero, only one spte points at this page and
parent_ptes points at this single spte, otherwise, there exists multiple
sptes pointing at this page and (parent_ptes & ~0x1) points at a data
structure with a list of parent_ptes.
structure with a list of parent sptes.
unsync:
If true, then the translations in this page may not match the guest's
translation. This is equivalent to the state of the tlb when a pte is

26
arch/x86/kvm/mmu.c
View File

@ -1098,17 +1098,23 @@ struct rmap_iterator {
static u64 *rmap_get_first(struct kvm_rmap_head *rmap_head,
struct rmap_iterator *iter)
{
u64 *sptep;
if (!rmap_head->val)
return NULL;
if (!(rmap_head->val & 1)) {
iter->desc = NULL;
return (u64 *)rmap_head->val;
sptep = (u64 *)rmap_head->val;
goto out;
}
iter->desc = (struct pte_list_desc *)(rmap_head->val & ~1ul);
iter->pos = 0;
return iter->desc->sptes[iter->pos];
sptep = iter->desc->sptes[iter->pos];
out:
BUG_ON(!is_shadow_present_pte(*sptep));
return sptep;
}
/*
@ -1118,14 +1124,14 @@ static u64 *rmap_get_first(struct kvm_rmap_head *rmap_head,
*/
static u64 *rmap_get_next(struct rmap_iterator *iter)
{
u64 *sptep;
if (iter->desc) {
if (iter->pos < PTE_LIST_EXT - 1) {
u64 *sptep;
++iter->pos;
sptep = iter->desc->sptes[iter->pos];
if (sptep)
return sptep;
goto out;
}
iter->desc = iter->desc->more;
@ -1133,17 +1139,20 @@ static u64 *rmap_get_next(struct rmap_iterator *iter)
if (iter->desc) {
iter->pos = 0;
/* desc->sptes[0] cannot be NULL */
return iter->desc->sptes[iter->pos];
sptep = iter->desc->sptes[iter->pos];
goto out;
}
}
return NULL;
out:
BUG_ON(!is_shadow_present_pte(*sptep));
return sptep;
}
#define for_each_rmap_spte(_rmap_head_, _iter_, _spte_) \
for (_spte_ = rmap_get_first(_rmap_head_, _iter_); \
_spte_ && ({BUG_ON(!is_shadow_present_pte(*_spte_)); 1;}); \
_spte_ = rmap_get_next(_iter_))
_spte_; _spte_ = rmap_get_next(_iter_))
static void drop_spte(struct kvm *kvm, u64 *sptep)
{
@ -1358,7 +1367,6 @@ static bool kvm_zap_rmapp(struct kvm *kvm, struct kvm_rmap_head *rmap_head)
bool flush = false;
while ((sptep = rmap_get_first(rmap_head, &iter))) {
BUG_ON(!(*sptep & PT_PRESENT_MASK));
rmap_printk("%s: spte %p %llx.\n", __func__, sptep, *sptep);
drop_spte(kvm, sptep);