linux-kernel - Re: [PATCH 03/10] KVM: SVM: Move nested INTR #vmexit into preemtible code

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Message-ID: <20091007205852.GA7692@amt.cnet>
Date:	Wed, 7 Oct 2009 17:58:52 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/10] KVM: SVM: Move nested INTR #vmexit into
	preemtible code

On Wed, Oct 07, 2009 at 04:31:21PM +0200, Joerg Roedel wrote:
> This patch makes use of the KVM_REQ_VMEXIT to move the
> emulation of #vmexit(INTR) out of non-preemptible code.
> 
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kvm/svm.c |   18 ++++++++++++++++--
>  1 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index b6ce1a9..7015680 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1379,8 +1379,14 @@ static inline int nested_svm_intr(struct vcpu_svm *svm)
>  
>  	svm->vmcb->control.exit_code = SVM_EXIT_INTR;
>  
> -	if (nested_svm_exit_handled(svm)) {
> -		nsvm_printk("VMexit -> INTR\n");
> +	if (svm->nested.intercept & 1ULL) {
> +		/*
> +		 * The #vmexit can't be emulated here directly because this
> +		 * code path runs with irqs and preemtion disabled and a
> +		 * #vmexit emulation might sleep. Only set the request bit for
> +		 * the #vmexit here.
> +		 */
> +		set_bit(KVM_REQ_VMEXIT, &svm->vcpu.requests);
>  		return 1;
>  	}

What if you keep this internal to SVM? Proceed to svm_vcpu_run and
return, do the emulation on the exit handler.

Then there's no need for the request bit (VMX does that, see
vmx_vcpu_run).

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