linux-kernel - Re: [PATCH 3/8] KVM: x86: leave vcpu->arch.pio.count alone in emulator_pio_in

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Date:   Fri, 22 Oct 2021 02:12:55 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     fwilhelm@...gle.com, seanjc@...gle.com, oupton@...gle.com,
        stable@...r.kernel.org
Subject: Re: [PATCH 3/8] KVM: x86: leave vcpu->arch.pio.count alone in
 emulator_pio_in_out

On Wed, 2021-10-13 at 12:56 -0400, Paolo Bonzini wrote:
> Currently emulator_pio_in clears vcpu->arch.pio.count twice if
> emulator_pio_in_out performs kernel PIO.  Move the clear into
> emulator_pio_out where it is actually necessary.
> 
> No functional change intended.
> 
> Cc: stable@...r.kernel.org
> Fixes: 7ed9abfe8e9f ("KVM: SVM: Support string IO operations for an SEV-ES guest")
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 722f5fcf76e1..218877e297e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6914,10 +6914,8 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
>  	vcpu->arch.pio.count  = count;
>  	vcpu->arch.pio.size = size;
>  
> -	if (!kernel_pio(vcpu, vcpu->arch.pio_data)) {
> -		vcpu->arch.pio.count = 0;
> +	if (!kernel_pio(vcpu, vcpu->arch.pio_data))
>  		return 1;
> -	}
>  
>  	vcpu->run->exit_reason = KVM_EXIT_IO;
>  	vcpu->run->io.direction = in ? KVM_EXIT_IO_IN : KVM_EXIT_IO_OUT;
> @@ -6963,9 +6961,16 @@ static int emulator_pio_out(struct kvm_vcpu *vcpu, int size,
>  			    unsigned short port, const void *val,
>  			    unsigned int count)
>  {
> +	int ret;
> +
>  	memcpy(vcpu->arch.pio_data, val, size * count);
>  	trace_kvm_pio(KVM_PIO_OUT, port, size, count, vcpu->arch.pio_data);
> -	return emulator_pio_in_out(vcpu, size, port, (void *)val, count, false);
> +	ret = emulator_pio_in_out(vcpu, size, port, (void *)val, count, false);
> +	if (ret)
> +                vcpu->arch.pio.count = 0;
> +
> +        return ret;
> +
>  }
>  
>  static int emulator_pio_out_emulated(struct x86_emulate_ctxt *ctxt,

Makes sense, now that both emulator_pio_in and emulator_pio_out clear the arch.pio.count once.

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky