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

From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Maxim Levitsky <mlevitsk@redhat.com>, kvm@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	Sean Christopherson <seanjc@google.com>,
	linux-kernel@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused cmpxchg to be not atomic
Date: Thu, 12 May 2022 14:45:42 +0200	[thread overview]
Message-ID: <875ymayl55.fsf@redhat.com> (raw)
In-Reply-To: <20220512101420.306759-1-mlevitsk@redhat.com>

Maxim Levitsky <mlevitsk@redhat.com> writes:

> Fixes: 1c2361f667f36 ("KVM: x86: Use __try_cmpxchg_user() to emulate atomic accesses")
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.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.

In case the fix is not squashed with 1c2361f667f36, the above should
really go before '---'.

>
> 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))

Looks like a typo indeed, so

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

>  		goto emul_write;
>  
>  	hva += offset_in_page(gpa);

-- 
Vitaly