linux-kernel - RE: [PATCH 5/9] KVM: x86: unify handling of interrupt window

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Date:	Thu, 6 Aug 2015 06:50:14 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
CC:	Steve Rutherford <srutherford@...gle.com>,
	"rkrcmar@...hat.com" <rkrcmar@...hat.com>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH 5/9] KVM: x86: unify handling of interrupt window



> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org
> [mailto:linux-kernel-owner@...r.kernel.org] On Behalf Of Paolo Bonzini
> Sent: Wednesday, August 05, 2015 11:24 PM
> To: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
> Cc: Steve Rutherford; rkrcmar@...hat.com
> Subject: [PATCH 5/9] KVM: x86: unify handling of interrupt window
> 
> The interrupt window is currently checked twice, once in vmx.c/svm.c and
> once in dm_request_for_irq_injection.  The only difference is the extra
> check for kvm_arch_interrupt_allowed in dm_request_for_irq_injection,
> and the different return value (EINTR/KVM_EXIT_INTR for vmx.c/svm.c vs.
> 0/KVM_EXIT_IRQ_WINDOW_OPEN for dm_request_for_irq_injection).
> 
> However, dm_request_for_irq_injection is basically dead code!  Revive it
> by removing the checks in vmx.c and svm.c's vmexit handlers, and
> fixing the returned values for the dm_request_for_irq_injection case.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/svm.c | 13 -------------
>  arch/x86/kvm/vmx.c | 11 -----------
>  arch/x86/kvm/x86.c |  4 ++--
>  3 files changed, 2 insertions(+), 26 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 222439fd73d4..189e46479dd5 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3396,24 +3396,11 @@ static int msr_interception(struct vcpu_svm
> *svm)
> 
>  static int interrupt_window_interception(struct vcpu_svm *svm)
>  {
> -	struct kvm_run *kvm_run = svm->vcpu.run;
> -
>  	kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
>  	svm_clear_vintr(svm);
>  	svm->vmcb->control.int_ctl &= ~V_IRQ_MASK;
>  	mark_dirty(svm->vmcb, VMCB_INTR);
>  	++svm->vcpu.stat.irq_window_exits;
> -	/*
> -	 * If the user space waits to inject interrupts, exit as soon as
> -	 * possible
> -	 */
> -	if (!lapic_in_kernel(&svm->vcpu) &&
> -	    kvm_run->request_interrupt_window &&
> -	    !kvm_cpu_has_interrupt(&svm->vcpu)) {
> -		kvm_run->exit_reason = KVM_EXIT_IRQ_WINDOW_OPEN;
> -		return 0;
> -	}
> -
>  	return 1;
>  }
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index ef15dc72284b..4cf25b90dbe0 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5524,17 +5524,6 @@ static int handle_interrupt_window(struct
> kvm_vcpu *vcpu)
>  	kvm_make_request(KVM_REQ_EVENT, vcpu);
> 
>  	++vcpu->stat.irq_window_exits;
> -
> -	/*
> -	 * If the user space waits to inject interrupts, exit as soon as
> -	 * possible
> -	 */
> -	if (!lapic_in_kernel(vcpu) &&
> -	    vcpu->run->request_interrupt_window &&
> -	    !kvm_cpu_has_interrupt(vcpu)) {
> -		vcpu->run->exit_reason = KVM_EXIT_IRQ_WINDOW_OPEN;
> -		return 0;
> -	}
>  	return 1;
>  }

Is it possible to adjust the code here and remove the later checking in x86.c?
In that case, we can avoid calling dm_request_for_irq_injection(vcpu) for
VM exit. Basically dm_request_for_irq_injection() did the following
checks:

- The same as in handle_interrupt_window() below:

        if (!irqchip_in_kernel(vcpu->kvm) &&
            vcpu->run->request_interrupt_window &&
            !kvm_cpu_has_interrupt(vcpu))

- kvm_arch_interrupt_allowed(vcpu), in which, most of the conditions
are guaranteed by interrupt window exits, the only one I am not sure
how to handle is ' to_vmx(vcpu)->nested.nested_run_pending'.

Thanks,
Feng

> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index daa6d4fe97fe..62362fed4169 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6475,8 +6475,8 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
>  			kvm_inject_pending_timer_irqs(vcpu);
> 
>  		if (dm_request_for_irq_injection(vcpu)) {
> -			r = -EINTR;
> -			vcpu->run->exit_reason = KVM_EXIT_INTR;
> +			r = 0;
> +			vcpu->run->exit_reason = KVM_EXIT_IRQ_WINDOW_OPEN;
>  			++vcpu->stat.request_irq_exits;
>  			break;
>  		}
> --
> 1.8.3.1
> 
> 
> --
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