Date:   Tue, 26 Oct 2021 16:56:30 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com
Subject: Re: [PATCH 10/13] KVM: x86: wean in-kernel PIO from vcpu->arch.pio*

On Fri, 2021-10-22 at 11:36 -0400, Paolo Bonzini wrote:
> Make emulator_pio_in_out operate directly on the provided buffer
> as long as PIO is handled inside KVM.
> 
> For input operations, this means that, in the case of in-kernel
> PIO, __emulator_pio_in does not have to be always followed
> by complete_emulator_pio_in.  This affects emulator_pio_in and
> kvm_sev_es_ins; for the latter, that is why the call moves from
> advance_sev_es_emulated_ins to complete_sev_es_emulated_ins.
> 
> For output, it means that vcpu->pio.count is never set unnecessarily
> and there is no need to clear it.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 63 +++++++++++++++++++++-------------------------
>  1 file changed, 28 insertions(+), 35 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7c421d9fbcb6..e3d3c13fe803 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6894,16 +6894,6 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
>  	int r;
>  
>  	WARN_ON_ONCE(vcpu->arch.pio.count);
> -	vcpu->arch.pio.port = port;
> -	vcpu->arch.pio.in = in;
> -	vcpu->arch.pio.count = count;
> -	vcpu->arch.pio.size = size;
> -	if (in)
> -		memset(vcpu->arch.pio_data, 0, size * count);
> -	else
> -		memcpy(vcpu->arch.pio_data, data, size * count);
> -	data = vcpu->arch.pio_data;
> -
>  	for (i = 0; i < count; i++) {
>  		if (in)
>  			r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, port, size, data);
> @@ -6917,6 +6907,16 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
>  
>  userspace_io:
>  	WARN_ON(i != 0);
> +	vcpu->arch.pio.port = port;
> +	vcpu->arch.pio.in = in;
> +	vcpu->arch.pio.count = count;
> +	vcpu->arch.pio.size = size;
> +
> +	if (in)
> +		memset(vcpu->arch.pio_data, 0, size * count);
> +	else
> +		memcpy(vcpu->arch.pio_data, data, size * count);
> +
>  	vcpu->run->exit_reason = KVM_EXIT_IO;
>  	vcpu->run->io.direction = in ? KVM_EXIT_IO_IN : KVM_EXIT_IO_OUT;
>  	vcpu->run->io.size = size;
> @@ -6928,9 +6928,13 @@ static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
>  }
>  
>  static int __emulator_pio_in(struct kvm_vcpu *vcpu, int size,
> -			     unsigned short port, unsigned int count)
> +			     unsigned short port, void *val, unsigned int count)
>  {
> -	return emulator_pio_in_out(vcpu, size, port, NULL, count, true);
> +	int r = emulator_pio_in_out(vcpu, size, port, val, count, true);
> +	if (r)
> +		trace_kvm_pio(KVM_PIO_IN, port, size, count, val);

I have an idea to move the tracepoints that happen before userspace exit (this
one when we have in-kernel emulation, and one in emulator_pio_out to  emulator_pio_in_out.

> +
> +	return r;
>  }
>  
>  static void complete_emulator_pio_in(struct kvm_vcpu *vcpu, void *val)
> @@ -6947,17 +6951,12 @@ static int emulator_pio_in(struct kvm_vcpu *vcpu, int size,
>  {
>  	if (vcpu->arch.pio.count) {
>  		/* Complete previous iteration.  */
> +		WARN_ON(count != vcpu->arch.pio.count);
> +		complete_emulator_pio_in(vcpu, val);
> +		return 1;
>  	} else {
> -		int r = __emulator_pio_in(vcpu, size, port, count);
> -		if (!r)
> -			return r;
> -
> -		/* Results already available, fall through.  */
> +		return __emulator_pio_in(vcpu, size, port, val, count);
>  	}
> -
> -	WARN_ON(count != vcpu->arch.pio.count);
> -	complete_emulator_pio_in(vcpu, val);
> -	return 1;
>  }
>  
>  static int emulator_pio_in_emulated(struct x86_emulate_ctxt *ctxt,
> @@ -6972,14 +6971,8 @@ static int emulator_pio_out(struct kvm_vcpu *vcpu, int size,
>  			    unsigned short port, const void *val,
>  			    unsigned int count)
>  {
> -	int ret;
> -
>  	trace_kvm_pio(KVM_PIO_OUT, port, size, count, val);
> -	ret = emulator_pio_in_out(vcpu, size, port, (void *)val, count, false);
> -	if (ret)
> -                vcpu->arch.pio.count = 0;
> -
> -        return ret;
> +	return emulator_pio_in_out(vcpu, size, port, (void *)val, count, false);
>  }
>  
>  static int emulator_pio_out_emulated(struct x86_emulate_ctxt *ctxt,
> @@ -12422,20 +12415,20 @@ static int kvm_sev_es_outs(struct kvm_vcpu *vcpu, unsigned int size,
>  static int kvm_sev_es_ins(struct kvm_vcpu *vcpu, unsigned int size,
>  			  unsigned int port);
>  
> -static void advance_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
> +static void advance_sev_es_emulated_ins(struct kvm_vcpu *vcpu, unsigned count, int size)
>  {
> -	unsigned count = vcpu->arch.pio.count;
> -	complete_emulator_pio_in(vcpu, vcpu->arch.sev_pio_data);
>  	vcpu->arch.sev_pio_count -= count;
> -	vcpu->arch.sev_pio_data += count * vcpu->arch.pio.size;
> +	vcpu->arch.sev_pio_data += count * size;
>  }
>  
>  static int complete_sev_es_emulated_ins(struct kvm_vcpu *vcpu)
>  {
> +	unsigned count = vcpu->arch.pio.count;
>  	int size = vcpu->arch.pio.size;
>  	int port = vcpu->arch.pio.port;
>  
> -	advance_sev_es_emulated_ins(vcpu);
> +	complete_emulator_pio_in(vcpu, vcpu->arch.sev_pio_data);
> +	advance_sev_es_emulated_ins(vcpu, count, size);
>  	if (vcpu->arch.sev_pio_count)
>  		return kvm_sev_es_ins(vcpu, size, port);
>  	return 1;
> @@ -12447,11 +12440,11 @@ static int kvm_sev_es_ins(struct kvm_vcpu *vcpu, unsigned int size,
>  	for (;;) {
>  		unsigned int count =
>  			min_t(unsigned int, PAGE_SIZE / size, vcpu->arch.sev_pio_count);
> -		if (!__emulator_pio_in(vcpu, size, port, count))
> +		if (!__emulator_pio_in(vcpu, size, port, vcpu->arch.sev_pio_data, count))
>  			break;
>  
>  		/* Emulation done by the kernel.  */
> -		advance_sev_es_emulated_ins(vcpu);
> +		advance_sev_es_emulated_ins(vcpu, count, size);
>  		if (!vcpu->arch.sev_pio_count)
>  			return 1;
>  	}

Looks good, was a bit difficult to follow, so I might have missed something.

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

Best regards,
	Maxim Levitsky

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