linux-kernel - Re: [PATCH v2 07/10] KVM: SVM: Use guard(mutex) to simplify SNP AP Creation error handling

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Message-ID: <8e9b3db1-2b74-4db1-8daf-3b66b407ad9a@amd.com>
Date: Thu, 27 Feb 2025 17:51:23 +0100
From: "Gupta, Pankaj" <pankaj.gupta@....com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Naveen N Rao <naveen@...nel.org>, Kim Phillips <kim.phillips@....com>,
 Tom Lendacky <thomas.lendacky@....com>, Alexey Kardashevskiy <aik@....com>
Subject: Re: [PATCH v2 07/10] KVM: SVM: Use guard(mutex) to simplify SNP AP
 Creation error handling

On 2/27/2025 2:25 AM, Sean Christopherson wrote:
> Use guard(mutex) in sev_snp_ap_creation() and modify the error paths to
> return directly instead of jumping to a common exit point.
> 
> No functional change intended.
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Pankaj Gupta <pankaj.gupta@....com>

> ---
>   arch/x86/kvm/svm/sev.c | 22 ++++++----------------
>   1 file changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index ccac840ee7be..dd9511a2254b 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3938,7 +3938,6 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>   	struct vcpu_svm *target_svm;
>   	unsigned int request;
>   	unsigned int apic_id;
> -	int ret;
>   
>   	request = lower_32_bits(svm->vmcb->control.exit_info_1);
>   	apic_id = upper_32_bits(svm->vmcb->control.exit_info_1);
> @@ -3951,11 +3950,9 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>   		return -EINVAL;
>   	}
>   
> -	ret = 0;
> -
>   	target_svm = to_svm(target_vcpu);
>   
> -	mutex_lock(&target_svm->sev_es.snp_vmsa_mutex);
> +	guard(mutex)(&target_svm->sev_es.snp_vmsa_mutex);
>   
>   	switch (request) {
>   	case SVM_VMGEXIT_AP_CREATE_ON_INIT:
> @@ -3963,15 +3960,13 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>   		if (vcpu->arch.regs[VCPU_REGS_RAX] != sev->vmsa_features) {
>   			vcpu_unimpl(vcpu, "vmgexit: mismatched AP sev_features [%#lx] != [%#llx] from guest\n",
>   				    vcpu->arch.regs[VCPU_REGS_RAX], sev->vmsa_features);
> -			ret = -EINVAL;
> -			goto out;
> +			return -EINVAL;
>   		}
>   
>   		if (!page_address_valid(vcpu, svm->vmcb->control.exit_info_2)) {
>   			vcpu_unimpl(vcpu, "vmgexit: invalid AP VMSA address [%#llx] from guest\n",
>   				    svm->vmcb->control.exit_info_2);
> -			ret = -EINVAL;
> -			goto out;
> +			return -EINVAL;
>   		}
>   
>   		/*
> @@ -3985,8 +3980,7 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>   			vcpu_unimpl(vcpu,
>   				    "vmgexit: AP VMSA address [%llx] from guest is unsafe as it is 2M aligned\n",
>   				    svm->vmcb->control.exit_info_2);
> -			ret = -EINVAL;
> -			goto out;
> +			return -EINVAL;
>   		}
>   
>   		target_svm->sev_es.snp_vmsa_gpa = svm->vmcb->control.exit_info_2;
> @@ -3997,8 +3991,7 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>   	default:
>   		vcpu_unimpl(vcpu, "vmgexit: invalid AP creation request [%#x] from guest\n",
>   			    request);
> -		ret = -EINVAL;
> -		goto out;
> +		return -EINVAL;
>   	}
>   
>   	target_svm->sev_es.snp_ap_waiting_for_reset = true;
> @@ -4012,10 +4005,7 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>   		kvm_vcpu_kick(target_vcpu);
>   	}
>   
> -out:
> -	mutex_unlock(&target_svm->sev_es.snp_vmsa_mutex);
> -
> -	return ret;
> +	return 0;
>   }
>   
>   static int snp_handle_guest_req(struct vcpu_svm *svm, gpa_t req_gpa, gpa_t resp_gpa)