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KVM: x86/mmu: Preserve nested TDP shadow page tables if they are used as roots

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kvm_mmu_zap_oldest_mmu_pages() excludes a shadow page whose root_count
is non-zero from top-level reclaim, because such a page cannot be
freed. The path in mmu_page_zap_pte() that recursively zaps a parentless
nested TDP child has no such check. As a result, a shadow page can
be zapped even if the page itself can't be freed; as the comment in
kvm_mmu_zap_oldest_mmu_pages() notes, zapping it will just force vCPUs
to rebuild the page.

As in top-level reclaim, do not recursively prepare zapping of a
nested TDP child whose root_count is non-zero.

Fixes: 2de4085ccc ("KVM: x86/MMU: Recursively zap nested TDP SPs when zapping last/only parent")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Hyunwoo Kim 2026-07-12 10:14:50 +09:00 committed by Paolo Bonzini
parent 2abd5287f0
commit 7a2c70e777
1 changed files with 1 additions and 0 deletions
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arch/x86/kvm/mmu/mmu.c
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@ -2642,6 +2642,7 @@ static int mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
*/
if (tdp_enabled && invalid_list &&
child->role.guest_mode &&
!child->root_count &&
!atomic_long_read(&child->parent_ptes.val))
return kvm_mmu_prepare_zap_page(kvm, child,
invalid_list);