linux-kernel - [PATCH v6 8/8] KVM: x86/mmu: WARN if TDP MMU SP disallows hugepage after being zapped

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Date:   Wed, 19 Oct 2022 16:56:18 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mingwei Zhang <mizhang@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Yan Zhao <yan.y.zhao@...el.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v6 8/8] KVM: x86/mmu: WARN if TDP MMU SP disallows hugepage
 after being zapped

Extend the accounting sanity check in kvm_recover_nx_huge_pages() to the
TDP MMU, i.e. verify that zapping a shadow page unaccounts the disallowed
NX huge page regardless of the MMU type.  Recovery runs while holding
mmu_lock for write and so it should be impossible to get false positives
on the WARN.

Suggested-by: Yan Zhao <yan.y.zhao@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 14674c9e10f7..dfd1656232ad 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -6864,12 +6864,11 @@ static void kvm_recover_nx_huge_pages(struct kvm *kvm)
 				      struct kvm_mmu_page,
 				      possible_nx_huge_page_link);
 		WARN_ON_ONCE(!sp->nx_huge_page_disallowed);
-		if (is_tdp_mmu_page(sp)) {
+		if (is_tdp_mmu_page(sp))
 			flush |= kvm_tdp_mmu_zap_sp(kvm, sp);
-		} else {
+		else
 			kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list);
-			WARN_ON_ONCE(sp->nx_huge_page_disallowed);
-		}
+		WARN_ON_ONCE(sp->nx_huge_page_disallowed);
 
 		if (need_resched() || rwlock_needbreak(&kvm->mmu_lock)) {
 			kvm_mmu_remote_flush_or_zap(kvm, &invalid_list, flush);
-- 
2.38.0.413.g74048e4d9e-goog