linux-kernel - [PATCH 16/28] KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in non-atomic path

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Message-Id: <20211120045046.3940942-17-seanjc@google.com>
Date:   Sat, 20 Nov 2021 04:50:34 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Hou Wenlong <houwenlong93@...ux.alibaba.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 16/28] KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in
 non-atomic path

WARN if the new_spte being set by __tdp_mmu_set_spte() is a REMOVED_SPTE,
which is called out by the comment as being disallowed but not actually
checked.  Keep the WARN on the old_spte as well, because overwriting a
REMOVED_SPTE in the non-atomic path is also disallowed (as evidence by
lack of splats with the existing WARN).

Fixes: 08f07c800e9d ("KVM: x86/mmu: Flush TLBs after zap in TDP MMU PF handler")
Cc: Ben Gardon <bgardon@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 085f6b09e5f3..d9524b387221 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -638,13 +638,13 @@ static inline void __tdp_mmu_set_spte(struct kvm *kvm, struct tdp_iter *iter,
 	lockdep_assert_held_write(&kvm->mmu_lock);
 
 	/*
-	 * No thread should be using this function to set SPTEs to the
+	 * No thread should be using this function to set SPTEs to or from the
 	 * temporary removed SPTE value.
 	 * If operating under the MMU lock in read mode, tdp_mmu_set_spte_atomic
 	 * should be used. If operating under the MMU lock in write mode, the
 	 * use of the removed SPTE should not be necessary.
 	 */
-	WARN_ON(is_removed_spte(iter->old_spte));
+	WARN_ON(is_removed_spte(iter->old_spte) || is_removed_spte(new_spte));
 
 	kvm_tdp_mmu_write_spte(iter->sptep, new_spte);
 
-- 
2.34.0.rc2.393.gf8c9666880-goog