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

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Message-ID: <c7fa2932-c295-8663-a3ca-840b63d72fc2@amd.com>
Date: Mon, 24 Feb 2025 15:49:09 -0600
From: Tom Lendacky <thomas.lendacky@....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>,
 Alexey Kardashevskiy <aik@....com>
Subject: Re: [PATCH 07/10] KVM: SVM: Use guard(mutex) to simplify SNP AP
 Creation error handling

On 2/18/25 19:27, 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>
> ---
>  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 7f6c8fedb235..241cf7769508 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3940,7 +3940,6 @@ 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);
> @@ -3953,11 +3952,9 @@ 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:
> @@ -3965,15 +3962,13 @@ 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;
>  		}
>  
>  		/*
> @@ -3987,8 +3982,7 @@ 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;
> @@ -3999,8 +3993,7 @@ 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;
> @@ -4014,10 +4007,7 @@ 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)