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

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Date: Mon, 13 May 2024 18:53:24 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Nathan Chancellor <nathan@...nel.org>, Michael Roth <michael.roth@....com>
Cc: 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 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?

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