[PATCH 6.18.y v2] KVM: x86/mmu: Preserve nested TDP shadow page tables if they are used as roots
From: Sean Christopherson
Date: Tue Oct 20 2026 - 22:16:53 EST
From: Hyunwoo Kim <imv4bel@xxxxxxxxx>
[ Upstream commit 7a2c70e777a00c32ebafd376a6fe31ebb91c5b20 ]
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: 2de4085cccea ("KVM: x86/MMU: Recursively zap nested TDP SPs when zapping last/only parent")
Signed-off-by: Hyunwoo Kim <imv4bel@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 205d314a7583..1fa251ca4dcc 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2630,6 +2630,7 @@ 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);
base-commit: 2ff600d29ee478d0a8d46ef8a58afb5e038fe692
--
2.56.0.218.g1ec904b173-goog