linux-kernel - Re: [PULL 18/19] KVM: SEV: Provide support for SNP_EXTENDED_GUEST

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Message-ID: <20240513170535.je74yhujxpogijga@amd.com>
Date: Mon, 13 May 2024 12:05:35 -0500
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: Nathan Chancellor <nathan@...nel.org>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Sean Christopherson <seanjc@...gle.com>,
	<llvm@...ts.linux.dev>
Subject: Re: [PULL 18/19] KVM: SEV: Provide support for
 SNP_EXTENDED_GUEST_REQUEST NAE event

On Mon, May 13, 2024 at 06:53:24PM +0200, Paolo Bonzini wrote:
> On 5/13/24 17:19, Nathan Chancellor wrote:
> > > +static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
> > > +{
> > > +	int vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
> > > +	struct vcpu_svm *svm = to_svm(vcpu);
> > > +	unsigned long data_npages;
> > > +	sev_ret_code fw_err;
> > > +	gpa_t data_gpa;
> > > +
> > > +	if (!sev_snp_guest(vcpu->kvm))
> > > +		goto abort_request;
> > > +
> > > +	data_gpa = vcpu->arch.regs[VCPU_REGS_RAX];
> > > +	data_npages = vcpu->arch.regs[VCPU_REGS_RBX];
> > > +
> > > +	if (!IS_ALIGNED(data_gpa, PAGE_SIZE))
> > > +		goto abort_request;
> > 
> > [...]
> > 
> > > +abort_request:
> > > +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
> > > +	return 1; /* resume guest */
> > > +}
> > 
> > This patch is now in -next as commit 32fde9e18b3f ("KVM: SEV: Provide
> > support for SNP_EXTENDED_GUEST_REQUEST NAE event"), where it causes a
> > clang warning (or hard error when CONFIG_WERROR is enabled) [...]
> > Seems legitimate to me. What was the intention here?
> 
> Mike, I think this should just be 0?

Hi Paolo,

Yes, I was just about to submit a patch that does just that:

  https://github.com/mdroth/linux/commit/df55e9c5b97542fe037f5b5293c11a49f7c658ef

Sorry for the breakage,

Mike

> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c7a0971149f2..affb4fb47f91 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3911,7 +3911,6 @@ static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
>  	int vmm_ret = SNP_GUEST_VMM_ERR_GENERIC;
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  	unsigned long data_npages;
> -	sev_ret_code fw_err;
>  	gpa_t data_gpa;
>  	if (!sev_snp_guest(vcpu->kvm))
> @@ -3938,7 +3937,7 @@ static int snp_begin_ext_guest_req(struct kvm_vcpu *vcpu)
>  	return 0; /* forward request to userspace */
>  abort_request:
> -	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, fw_err));
> +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, SNP_GUEST_ERR(vmm_ret, 0));
>  	return 1; /* resume guest */
>  }
> Paolo
> 
>