Re: [PATCH 09/13] KVM: x86: move all vcpu->arch.pio* setup in emulator_pio_in_out

[Maxim Levitsky]

On Fri, 2021-10-22 at 11:36 -0400, Paolo Bonzini wrote:
> For now, this is basically an excuse to add back the void* argument to
> the function, while removing some knowledge of vcpu->arch.pio* from
> its callers.  The WARN that vcpu->arch.pio.count is zero is also
> extended to OUT operations.
> 
> We cannot do more as long as we have __emulator_pio_in always followed
> by complete_emulator_pio_in, which uses the vcpu->arch.pio* fields.
> But after fixing that, it will be possible to only populate the
> vcpu->arch.pio* fields on userspace exits.
> 
> No functional change intended.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>  arch/x86/kvm/trace.h |  2 +-
>  arch/x86/kvm/x86.c   | 18 ++++++++++--------
>  2 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
> index 03ebe368333e..1b0167ae9e24 100644
> --- a/arch/x86/kvm/trace.h
> +++ b/arch/x86/kvm/trace.h
> @@ -152,7 +152,7 @@ TRACE_EVENT(kvm_xen_hypercall,
>  
>  TRACE_EVENT(kvm_pio,
>  	TP_PROTO(unsigned int rw, unsigned int port, unsigned int size,
> -		 unsigned int count, void *data),
> +		 unsigned int count, const void *data),
>  	TP_ARGS(rw, port, size, count, data),
>  
>  	TP_STRUCT__entry(
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d6b8df7cea80..7c421d9fbcb6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6887,17 +6887,22 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
>  }
>  
>  static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
> -			       unsigned short port,
> +			       unsigned short port, void *data,
>  			       unsigned int count, bool in)
>  {
> -	void *data = vcpu->arch.pio_data;
>  	unsigned i;
>  	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;

It won't hurt to add the assert that size * count < PAGE_SIZE here.

> +	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)
> @@ -6925,9 +6930,7 @@ 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)
>  {
> -	WARN_ON(vcpu->arch.pio.count);
> -	memset(vcpu->arch.pio_data, 0, size * count);
> -	return emulator_pio_in_out(vcpu, size, port, count, true);
> +	return emulator_pio_in_out(vcpu, size, port, NULL, count, true);
>  }
>  
>  static void complete_emulator_pio_in(struct kvm_vcpu *vcpu, void *val)
> @@ -6971,9 +6974,8 @@ static int emulator_pio_out(struct kvm_vcpu *vcpu, int size,
>  {
>  	int ret;
>  
> -	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, count, false);
> +	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;
>  

Makes sense.
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>

Best regards,
	Maxim Levitsky