linux-kernel - Re: [PATCH] KVM: SVM: Remove bogus WARN and emulation if guest #GPs with EFER.SVME=1

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Date:   Thu, 4 Feb 2021 09:20:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     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, Bandan Das <bsd@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH] KVM: SVM: Remove bogus WARN and emulation if guest #GPs
 with EFER.SVME=1

On 04/02/21 03:35, Sean Christopherson wrote:
> Immediately reinject #GP (if intercepted) if the VMware backdoor is
> disabled and the instruction is not affected by the erratum that causes
> bogus #GPs on SVM instructions.  It is completely reasonable for the
> guest to take a #GP(0) with EFER.SVME=1, e.g. when probing an MSR, and
> attempting emulation on an unknown instruction is obviously not good.
> 
> Fixes: b3f4e11adc7d ("KVM: SVM: Add emulation support for #GP triggered by SVM instructions")
> Cc: Bandan Das <bsd@...hat.com>
> Cc: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/svm/svm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index f53e6377a933..707a2f85bcc6 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2263,7 +2263,8 @@ static int gp_interception(struct vcpu_svm *svm)
>   	opcode = svm_instr_opcode(vcpu);
>   
>   	if (opcode == NONE_SVM_INSTR) {
> -		WARN_ON_ONCE(!enable_vmware_backdoor);
> +		if (!enable_vmware_backdoor)
> +			goto reinject;
>   
>   		/*
>   		 * VMware backdoor emulation on #GP interception only handles
> 

Squashed, thanks.

Paolo