linux-kernel - Re: [PATCH 5/8] KVM: x86: split the two parts of emulator_pio

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Date:   Fri, 22 Oct 2021 02:14:29 +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 5/8] KVM: x86: split the two parts of emulator_pio_in

On Wed, 2021-10-13 at 12:56 -0400, Paolo Bonzini wrote:
> emulator_pio_in handles both the case where the data is pending in
> vcpu->arch.pio.count, and the case where I/O has to be done via either
> an in-kernel device or a userspace exit.  For SEV-ES we would like
> to split these, to identify clearly the moment at which the
> sev_pio_data is consumed.  To this end, create two different
> functions: __emulator_pio_in fills in vcpu->arch.pio.count, while
> complete_emulator_pio_in clears it and releases vcpu->arch.pio.data.
> 
> While at it, remove the void* argument also from emulator_pio_in_out.
s/remove the void* argument/remove the unused 'void* val' argument/ maybe?
> 
> 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 | 42 +++++++++++++++++++++++-------------------
>  1 file changed, 23 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8880dc36a2b4..07d9533b471d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6906,7 +6906,7 @@ static int kernel_pio(struct kvm_vcpu *vcpu, void *pd)
>  }
>  
>  static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
> -			       unsigned short port, void *val,
> +			       unsigned short port,
>  			       unsigned int count, bool in)
>  {
>  	vcpu->arch.pio.port = port;
> @@ -6927,26 +6927,31 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
>  	return 0;
>  }
>  
> -static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
> -			   unsigned short port, void *val, unsigned int count)
> +static int __emulator_pio_in(struct kvm_vcpu *vcpu, int size,
> +			     unsigned short port, unsigned int count)
>  {
> -	int ret;
> -
> -	if (vcpu->arch.pio.count)
> -		goto data_avail;
> -
> +	WARN_ON(vcpu->arch.pio.count);
>  	memset(vcpu->arch.pio_data, 0, size * count);
> +	return emulator_pio_in_out(vcpu, size, port, count, true);
> +}
>  
> -	ret = emulator_pio_in_out(vcpu, size, port, val, count, true);
> -	if (ret) {
> -data_avail:
> -		memcpy(val, vcpu->arch.pio_data, size * count);
> -		trace_kvm_pio(KVM_PIO_IN, port, size, count, vcpu->arch.pio_data);
> -		vcpu->arch.pio.count = 0;
> -		return 1;
> -	}
> +static void complete_emulator_pio_in(struct kvm_vcpu *vcpu, int size,
> +				    unsigned short port, void *val)
> +{
> +	memcpy(val, vcpu->arch.pio_data, size * vcpu->arch.pio.count);
> +	trace_kvm_pio(KVM_PIO_IN, port, size, vcpu->arch.pio.count, vcpu->arch.pio_data);
> +	vcpu->arch.pio.count = 0;
> +}
>  
> -	return 0;
> +static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
> +			   unsigned short port, void *val, unsigned int count)
> +{
> +	if (!vcpu->arch.pio.count && !__emulator_pio_in(vcpu, size, port, count))
> +		return 0;
^^ maybe I would add a comment here about the fact that kernel completed the
emulation when returing here.

> +
> +	WARN_ON(count != vcpu->arch.pio.count);
> +	complete_emulator_pio_in(vcpu, size, port, val);
> +	return 1;
>  }
>  
>  static int emulator_pio_in_emulated(struct x86_emulate_ctxt *ctxt,
> @@ -6965,12 +6970,11 @@ static int emulator_pio_out(struct kvm_vcpu *vcpu, int size,
>  
>  	memcpy(vcpu->arch.pio_data, val, size * count);
>  	trace_kvm_pio(KVM_PIO_OUT, port, size, count, vcpu->arch.pio_data);
> -	ret = emulator_pio_in_out(vcpu, size, port, (void *)val, count, false);
> +	ret = emulator_pio_in_out(vcpu, size, port, count, false);
>  	if (ret)
>                  vcpu->arch.pio.count = 0;
>  
>          return ret;
> -
>  }
>  
>  static int emulator_pio_out_emulated(struct x86_emulate_ctxt *ctxt,



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

Best regards,
	Maxim Levitsky