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

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Message-ID: <875ymayl55.fsf@redhat.com>
Date:   Thu, 12 May 2022 14:45:42 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, 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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused
 cmpxchg to be not atomic

Maxim Levitsky <mlevitsk@...hat.com> writes:

> 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.

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@...hat.com>

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

-- 
Vitaly