linux-kernel - [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused cmpxchg to be not atomic

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Message-Id: <20220512101420.306759-1-mlevitsk@redhat.com>
Date:   Thu, 12 May 2022 13:14:20 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused cmpxchg to be not atomic

Fixes: 1c2361f667f36 ("KVM: x86: Use __try_cmpxchg_user() to emulate atomic accesses")
Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Yes, this is the root cause of the TDP mmu leak I was doing debug of in the last week.
Non working cmpxchg on which TDP mmu relies makes it install two differnt shadow pages
under same spte.

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8ee8c91fa7625..79cabd3d97d22 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7329,7 +7329,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
 		goto emul_write;
 
 	hva = kvm_vcpu_gfn_to_hva(vcpu, gpa_to_gfn(gpa));
-	if (kvm_is_error_hva(addr))
+	if (kvm_is_error_hva(hva))
 		goto emul_write;
 
 	hva += offset_in_page(gpa);
-- 
2.26.3