linux-kernel - Re: [PATCH 4/8] KVM: SEV-ES: clean up kvm_sev_es

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Date:   Fri, 22 Oct 2021 02:14:05 +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 4/8] KVM: SEV-ES: clean up kvm_sev_es_ins/outs

On Wed, 2021-10-13 at 12:56 -0400, Paolo Bonzini wrote:
> Remove the data argument and pull setting vcpu->arch.sev_pio_data into
> the caller; remove unnecessary clearing of vcpu->arch.pio.count when
> emulation is done by the kernel.

You forgot to mention that you inlined the call to emulator_pio_out_emulated/emulator_pio_in_emulated.


> 
> 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 | 31 +++++++++++++++----------------
>  1 file changed, 15 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 218877e297e5..8880dc36a2b4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12382,34 +12382,32 @@ static int complete_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
>  }
>  
>  static int kvm_sev_es_outs(struct kvm_vcpu *vcpu, unsigned int size,
> -			   unsigned int port, void *data,  unsigned int count)
> +			   unsigned int port, unsigned int count)
>  {
> -	int ret;
> +	int ret = emulator_pio_out(vcpu, size, port,
> +				   vcpu->arch.sev_pio_data, count);
>  
> -	ret = emulator_pio_out_emulated(vcpu->arch.emulate_ctxt, size, port,
> -					data, count);
> -	if (ret)
> +	if (ret) {
> +		/* Emulation done by the kernel.  */
^^ This is a very good comment to have here!
>  		return ret;
> +	}
>  
>  	vcpu->arch.pio.count = 0;
^^^
I wonder what the rules are for clearing vcpu->arch.pio.count for userspace PIO vm exits.
Looks like complete_fast_pio_out clears it, but otherwise the only other place
that clears it in this case is x86_emulate_instruction when it restarts the instuction.
Do I miss something?


> -
>  	return 0;
>  }
>  
>  static int kvm_sev_es_ins(struct kvm_vcpu *vcpu, unsigned int size,
> -			  unsigned int port, void *data, unsigned int count)
> +			  unsigned int port, unsigned int count)
>  {
> -	int ret;
> +	int ret = emulator_pio_in(vcpu, size, port,
> +				  vcpu->arch.sev_pio_data, count);
>  
> -	ret = emulator_pio_in_emulated(vcpu->arch.emulate_ctxt, size, port,
> -				       data, count);
>  	if (ret) {
> -		vcpu->arch.pio.count = 0;
> -	} else {
> -		vcpu->arch.sev_pio_data = data;
> -		vcpu->arch.complete_userspace_io = complete_sev_es_emulated_ins;
> +		/* Emulation done by the kernel.  */
> +		return ret;
>  	}
>  
> +	vcpu->arch.complete_userspace_io = complete_sev_es_emulated_ins;
>  	return 0;
>  }
>  
> @@ -12417,8 +12415,9 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
>  			 unsigned int port, void *data,  unsigned int count,
>  			 int in)
>  {
> -	return in ? kvm_sev_es_ins(vcpu, size, port, data, count)
> -		  : kvm_sev_es_outs(vcpu, size, port, data, count);
> +	vcpu->arch.sev_pio_data = data;
> +	return in ? kvm_sev_es_ins(vcpu, size, port, count)
> +		  : kvm_sev_es_outs(vcpu, size, port, count);
>  }
>  EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);
>  

Looks OK to me, I might have missed something though.

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


Best regards,
	Maxim Levitsky