linux-kernel - Re: [PATCH v3] x86: svm: use kvm_fast_pio

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Date:	Thu, 12 Mar 2015 21:47:09 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Joel Schopp <joel.schopp@....com>
Cc:	Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	David Kaplan <David.Kaplan@....com>, rkrcmar@...hat.com,
	Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v3] x86: svm: use kvm_fast_pio_in()

On Mon, Mar 02, 2015 at 03:02:02PM -0600, Joel Schopp wrote:
> From: David Kaplan <David.Kaplan@....com>
> 
> We can make the in instruction go faster the same way the out instruction is
> already.
> 
> Changes from v2[Joel]:
> 	* changed rax from u32 to unsigned long
> 	* changed a couple return 0 to BUG_ON()
> 	* changed 8 to sizeof(new_rax)
> 	* added trace hook
> 	* removed redundant clearing of count
> Changes from v1[Joel]
> 	* Added kvm_fast_pio_in() implementation that was left out of v1
> 
> Signed-off-by: David Kaplan <David.Kaplan@....com>
> [extracted from larger unlrelated patch, forward ported, addressed reviews, tested]
> Signed-off-by: Joel Schopp <joel.schopp@....com>
> ---
>  arch/x86/include/asm/kvm_host.h |    1 +
>  arch/x86/kvm/svm.c              |    4 +++-
>  arch/x86/kvm/x86.c              |   30 ++++++++++++++++++++++++++++++
>  3 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index a236e39..b976824 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -931,6 +931,7 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr);
>  struct x86_emulate_ctxt;
>  
>  int kvm_fast_pio_out(struct kvm_vcpu *vcpu, int size, unsigned short port);
> +int kvm_fast_pio_in(struct kvm_vcpu *vcpu, int size, unsigned short port);
>  void kvm_emulate_cpuid(struct kvm_vcpu *vcpu);
>  int kvm_emulate_halt(struct kvm_vcpu *vcpu);
>  int kvm_emulate_wbinvd(struct kvm_vcpu *vcpu);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index d319e0c..f8c906b 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1899,7 +1899,7 @@ static int io_interception(struct vcpu_svm *svm)
>  	++svm->vcpu.stat.io_exits;
>  	string = (io_info & SVM_IOIO_STR_MASK) != 0;
>  	in = (io_info & SVM_IOIO_TYPE_MASK) != 0;
> -	if (string || in)
> +	if (string)
>  		return emulate_instruction(vcpu, 0) == EMULATE_DONE;
>  
>  	port = io_info >> 16;
> @@ -1907,6 +1907,8 @@ static int io_interception(struct vcpu_svm *svm)
>  	svm->next_rip = svm->vmcb->control.exit_info_2;
>  	skip_emulated_instruction(&svm->vcpu);
>  
> +	if (in)
> +		return kvm_fast_pio_in(vcpu, size, port);
>  	return kvm_fast_pio_out(vcpu, size, port);
>  }
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bd7a70b..d05efaf 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5463,6 +5463,36 @@ int kvm_fast_pio_out(struct kvm_vcpu *vcpu, int size, unsigned short port)
>  }
>  EXPORT_SYMBOL_GPL(kvm_fast_pio_out);
>  
> +static int complete_fast_pio(struct kvm_vcpu *vcpu)
> +{
> +	unsigned long new_rax = kvm_register_read(vcpu, VCPU_REGS_RAX);
> +
> +	BUG_ON(!vcpu->arch.pio.count);
> +	BUG_ON(vcpu->arch.pio.count * vcpu->arch.pio.size > sizeof(new_rax));
> +
> +	memcpy(&new_rax, vcpu, sizeof(new_rax));

Weird.

> +	trace_kvm_pio(KVM_PIO_IN, vcpu->arch.pio.port, vcpu->arch.pio.size,
> +		      vcpu->arch.pio.count, vcpu->arch.pio_data);
> +	kvm_register_write(vcpu, VCPU_REGS_RAX, new_rax);
> +	vcpu->arch.pio.count = 0;
> +	return 1;
> +}
> +
> +int kvm_fast_pio_in(struct kvm_vcpu *vcpu, int size, unsigned short port)
> +{
> +	unsigned long val;

Please zero initialize val.
Please check sanity of size.

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