linux-kernel - Re: [PATCH 08/13] KVM: x86: inline kernel

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Date:   Tue, 26 Oct 2021 16:55:59 +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 08/13] KVM: x86: inline kernel_pio into its sole caller

On Fri, 2021-10-22 at 11:36 -0400, Paolo Bonzini wrote:
> The caller of kernel_pio already has arguments for most of what kernel_pio
> fishes out of vcpu->arch.pio.  This is the first step towards ensuring that
> vcpu->arch.pio.* is only used when exiting to userspace.
> 
> We can now also WARN if emulated PIO performs successful in-kernel iterations
> before having to fall back to userspace.  The code is not ready for that, and
> it should never happen.
> 
> No functional change intended.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 39 +++++++++++++++++----------------------
>  1 file changed, 17 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b26647a5ea22..d6b8df7cea80 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6886,37 +6886,32 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt,
>  	return emulator_write_emulated(ctxt, addr, new, bytes, exception);
>  }
>  
> -static int kernel_pio(struct kvm_vcpu *vcpu, void *pd)
> -{
> -	int r = 0, i;
> -
> -	for (i = 0; i < vcpu->arch.pio.count; i++) {
> -		if (vcpu->arch.pio.in)
> -			r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, vcpu->arch.pio.port,
> -					    vcpu->arch.pio.size, pd);
> -		else
> -			r = kvm_io_bus_write(vcpu, KVM_PIO_BUS,
> -					     vcpu->arch.pio.port, vcpu->arch.pio.size,
> -					     pd);
> -		if (r)
> -			break;
> -		pd += vcpu->arch.pio.size;
> -	}
> -	return r;
> -}
> -
>  static int emulator_pio_in_out(struct kvm_vcpu *vcpu, int size,
>  			       unsigned short port,
>  			       unsigned int count, bool in)
>  {
> +	void *data = vcpu->arch.pio_data;
> +	unsigned i;
> +	int r;
> +
>  	vcpu->arch.pio.port = port;
>  	vcpu->arch.pio.in = in;
> -	vcpu->arch.pio.count  = count;
> +	vcpu->arch.pio.count = count;
>  	vcpu->arch.pio.size = size;
>  
> -	if (!kernel_pio(vcpu, vcpu->arch.pio_data))
> -		return 1;
> +	for (i = 0; i < count; i++) {
> +		if (in)
> +			r = kvm_io_bus_read(vcpu, KVM_PIO_BUS, port, size, data);
> +		else
> +			r = kvm_io_bus_write(vcpu, KVM_PIO_BUS, port, size, data);
> +		if (r)
> +			goto userspace_io;
> +		data += size;
> +	}
> +	return 1;
>  
> +userspace_io:
> +	WARN_ON(i != 0);
>  	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;

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

Best regards,
	Maxim Levitsky