From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH 1/2] KVM: x86 emulator: don't update vcpu state if instruction
 is restarted.
Date: Sat, 31 Jul 2010 20:25:13 +0300
Message-ID: <4C545C79.1010102@redhat.com>
References: <1280405513-579-1-git-send-email-gleb@redhat.com> <1280405513-579-2-git-send-email-gleb@redhat.com>
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Cc: mtosatti@redhat.com, kvm@vger.kernel.org
To: Gleb Natapov <gleb@redhat.com>
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  On 07/29/2010 03:11 PM, Gleb Natapov wrote:
> No need to update vcpu state since instruction is in the middle of the
> emulation.
>
> Signed-off-by: Gleb Natapov<gleb@redhat.com>
> ---
>   arch/x86/kvm/x86.c |   31 +++++++++++++------------------
>   1 files changed, 13 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 76fbc32..7e5f075 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4057,32 +4057,27 @@ restart:
>   		return handle_emulation_failure(vcpu);
>   	}
>
> -	toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
> -	kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
> -	memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
> -	kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
> +	r = EMULATE_DONE;
>
> -	if (vcpu->arch.emulate_ctxt.exception>= 0) {
> +	if (vcpu->arch.emulate_ctxt.exception>= 0)
>   		inject_emulated_exception(vcpu);
> -		return EMULATE_DONE;
> -	}
> -
> -	if (vcpu->arch.pio.count) {
> +	else if (vcpu->arch.pio.count) {
>   		if (!vcpu->arch.pio.in)
>   			vcpu->arch.pio.count = 0;
> -		return EMULATE_DO_MMIO;
> -	}
> -
> -	if (vcpu->mmio_needed) {
> +		r = EMULATE_DO_MMIO;
> +	} else if (vcpu->mmio_needed) {
>   		if (vcpu->mmio_is_write)
>   			vcpu->mmio_needed = 0;
> -		return EMULATE_DO_MMIO;
> -	}
> -
> -	if (vcpu->arch.emulate_ctxt.restart)
> +		r = EMULATE_DO_MMIO;
> +	} else if (vcpu->arch.emulate_ctxt.restart)
>   		goto restart;
>
> -	return EMULATE_DONE;
> +	toggle_interruptibility(vcpu, vcpu->arch.emulate_ctxt.interruptibility);
> +	kvm_x86_ops->set_rflags(vcpu, vcpu->arch.emulate_ctxt.eflags);
> +	memcpy(vcpu->arch.regs, c->regs, sizeof c->regs);
> +	kvm_rip_write(vcpu, vcpu->arch.emulate_ctxt.eip);
> +
> +	return r;
>   }
>   EXPORT_SYMBOL_GPL(emulate_instruction);
>

What about kvm-tpr-opt.c?  It uses rip after pio.

It's true that it usually doesn't go through the emulator.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.