linux-kernel - Re: [PATCH] KVM: SVM: Analyze is_guest_mode() in svm_vcpu

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Date:   Mon, 14 Sep 2020 13:43:07 -0700
From:   Krish Sadhukhan <krish.sadhukhan@...cle.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: SVM: Analyze is_guest_mode() in svm_vcpu_run()


On 9/13/20 11:55 PM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
>
> Analyze is_guest_mode() in svm_vcpu_run() instead of svm_exit_handlers_fastpath()
> in conformity with VMX version.
>
> Suggested-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>   arch/x86/kvm/svm/svm.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 3da5b2f..009035a 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3393,8 +3393,7 @@ static void svm_cancel_injection(struct kvm_vcpu *vcpu)
>   
>   static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
>   {
> -	if (!is_guest_mode(vcpu) &&
> -	    to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_MSR &&
> +	if (to_svm(vcpu)->vmcb->control.exit_code == SVM_EXIT_MSR &&
>   	    to_svm(vcpu)->vmcb->control.exit_info_1)
>   		return handle_fastpath_set_msr_irqoff(vcpu);
>   
> @@ -3580,6 +3579,10 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
>   		svm_handle_mce(svm);
>   
>   	svm_complete_interrupts(svm);
> +
> +	if (is_guest_mode(vcpu))
> +		return EXIT_FASTPATH_NONE;
> +
>   	exit_fastpath = svm_exit_handlers_fastpath(vcpu);
>   	return exit_fastpath;

Not related to your changes, but should we get rid of the variable 
'exit_fastpath' and just do,

         return svm_exit_handler_fastpath(vcpu);

It seems the variable isn't used anywhere else and svm_vcpu_run() 
doesn't return from anywhere else either.

Also, svm_exit_handlers_fastpath() doesn't have any other caller.  
Should we get rid of it as well ?


For your changes,

     Reviewed-by: Krish Sadhukhan <krish.sadhukhan@...cle.com>

>   }