linux-kernel - Re: [RESEND PATCH 01/13] KVM: x86: Relocate MMIO exit stats counting

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Message-ID: <87d0gwp7ix.fsf@vitty.brq.redhat.com>
Date:   Fri, 23 Aug 2019 11:15:18 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [RESEND PATCH 01/13] KVM: x86: Relocate MMIO exit stats counting

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Move the stat.mmio_exits update into x86_emulate_instruction().  This is
> both a bug fix, e.g. the current update flows will incorrectly increment
> mmio_exits on emulation failure, and a preparatory change to set the
> stage for eliminating EMULATE_DONE and company.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

This, however, makes me wonder why this is handled in x86-specific code
in the first place, can we just count KVM_EXIT_MMIO exits when handling
KVM_RUN?

> ---
>  arch/x86/kvm/mmu.c     | 2 --
>  arch/x86/kvm/vmx/vmx.c | 1 -
>  arch/x86/kvm/x86.c     | 2 ++
>  3 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 4c45ff0cfbd0..845e39d8a970 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -5437,8 +5437,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
>  	case EMULATE_DONE:
>  		return 1;
>  	case EMULATE_USER_EXIT:
> -		++vcpu->stat.mmio_exits;
> -		/* fall through */
>  	case EMULATE_FAIL:
>  		return 0;
>  	default:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 570a233e272b..18286e5b5983 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5200,7 +5200,6 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
>  		err = kvm_emulate_instruction(vcpu, 0);
>  
>  		if (err == EMULATE_USER_EXIT) {
> -			++vcpu->stat.mmio_exits;
>  			ret = 0;
>  			goto out;
>  		}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b4cfd786d0b6..cd425f54096a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6598,6 +6598,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
>  		}
>  		r = EMULATE_USER_EXIT;
>  	} else if (vcpu->mmio_needed) {
> +		++vcpu->stat.mmio_exits;
> +
>  		if (!vcpu->mmio_is_write)
>  			writeback = false;
>  		r = EMULATE_USER_EXIT;

-- 
Vitaly