linux-kernel - Re: [PATCH 06/10] KVM: SVM: Simplify request+kick logic in SNP AP Creation handling

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Message-ID: <d0b40cac-ba91-9e6b-7108-6a1e29f317c8@amd.com>
Date: Mon, 24 Feb 2025 15:48:12 -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 06/10] KVM: SVM: Simplify request+kick logic in SNP AP
 Creation handling

On 2/18/25 19:27, Sean Christopherson wrote:
> Drop the local "kick" variable and the unnecessary "fallthrough" logic
> from sev_snp_ap_creation(), and simply pivot on the request when deciding
> whether or not to immediate force a state update on the target vCPU.
> 
> 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 | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 8425198c5204..7f6c8fedb235 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;
> -	bool kick;
>  	int ret;
>  
>  	request = lower_32_bits(svm->vmcb->control.exit_info_1);
> @@ -3958,18 +3957,10 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>  
>  	target_svm = to_svm(target_vcpu);
>  
> -	/*
> -	 * The target vCPU is valid, so the vCPU will be kicked unless the
> -	 * request is for CREATE_ON_INIT.
> -	 */
> -	kick = true;
> -
>  	mutex_lock(&target_svm->sev_es.snp_vmsa_mutex);
>  
>  	switch (request) {
>  	case SVM_VMGEXIT_AP_CREATE_ON_INIT:
> -		kick = false;
> -		fallthrough;
>  	case SVM_VMGEXIT_AP_CREATE:
>  		if (vcpu->arch.regs[VCPU_REGS_RAX] != sev->vmsa_features) {
>  			vcpu_unimpl(vcpu, "vmgexit: mismatched AP sev_features [%#lx] != [%#llx] from guest\n",
> @@ -4014,7 +4005,11 @@ static int sev_snp_ap_creation(struct vcpu_svm *svm)
>  
>  	target_svm->sev_es.snp_ap_waiting_for_reset = true;
>  
> -	if (kick) {
> +	/*
> +	 * Unless Creation is deferred until INIT, signal the vCPU to update
> +	 * its state.
> +	 */
> +	if (request != SVM_VMGEXIT_AP_CREATE_ON_INIT) {
>  		kvm_make_request(KVM_REQ_UPDATE_PROTECTED_GUEST_STATE, target_vcpu);
>  		kvm_vcpu_kick(target_vcpu);
>  	}