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

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Message-ID: <a63c4589-6a2a-4ad8-8f58-2b791c8011d9@amd.com>
Date: Wed, 19 Feb 2025 07:19:07 +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 06/10] KVM: SVM: Simplify request+kick logic in SNP AP
 Creation handling

On 2/19/2025 2:27 AM, 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.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Straightforward cleanup.

Reviewed-by: Pankaj Gupta <pankaj.gupta@....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);
>   	}