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KVM: x86/mmu: Check all address spaces before skipping unsync

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mmu_try_to_unsync_pages() skips the shadow-page lookup when the
supplied memslot allows a hugepage, because a shadow page would disallow
hugepages.  But hugepage metadata is per-address-space while shadow pages
are shared across all address spaces.  With SMM, the other address space
can therefore have a shadow page even when the supplied memslot allows a
hugepage.

Check the corresponding memslot in the other address space before
taking the fast path.  Skip the shadow-page lookup only when all address
spaces allow a hugepage.

Fixes: b3ae3ceb55 ("KVM: x86/mmu: KVM: x86/mmu: Skip unsync when large pages are allowed")
Assisted-by: Codex:GPT-5
Signed-off-by: Jinu Kim <kimjw04271234@gmail.com>
[invert direction of the conditional. - Paolo]
Message-ID: <20260721103512.2136240-3-kimjw04271234@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jinu Kim
2026-07-21 19:35:12 +09:00
committed by Paolo Bonzini
parent 0f38453cdb
commit 2e8a2c1b03
1 changed files with 21 additions and 1 deletions
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22
arch/x86/kvm/mmu/mmu.c
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@@ -722,6 +722,26 @@ static struct kvm_lpage_info *lpage_info_slot(gfn_t gfn,
return &slot->arch.lpage_info[level - 2][idx];
}
static bool kvm_gfn_is_lpage_allowed(struct kvm *kvm,
const struct kvm_memory_slot *slot,
gfn_t gfn, int level)
{
const struct kvm_memory_slot *other_slot;
BUILD_BUG_ON(KVM_MAX_NR_ADDRESS_SPACES > 2);
if (lpage_info_slot(gfn, slot, level)->disallow_lpage)
return false;
if (kvm_arch_nr_memslot_as_ids(kvm) > 1) {
other_slot = __gfn_to_memslot(__kvm_memslots(kvm, slot->as_id ^ 1), gfn);
if (other_slot && lpage_info_slot(gfn, other_slot, level)->disallow_lpage)
return false;
}
return true;
}
/*
* The most significant bit in disallow_lpage tracks whether or not memory
* attributes are mixed, i.e. not identical for all gfns at the current level.
@@ -2968,7 +2988,7 @@ int mmu_try_to_unsync_pages(struct kvm *kvm, const struct kvm_memory_slot *slot,
* write-protected (see above), thus if the gfn can be mapped with a
* hugepage and isn't write-tracked, it can't have a shadow page.
*/
if (!lpage_info_slot(gfn, slot, PG_LEVEL_2M)->disallow_lpage)
if (kvm_gfn_is_lpage_allowed(kvm, slot, gfn, PG_LEVEL_2M))
return 0;
/*