linux-kernel - Re: [v2 resend] kvm/fpu: Enable eager restore kvm FPU for MPX

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Date:	Wed, 20 May 2015 11:50:16 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Liang Li <liang.z.li@...el.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	gleb@...nel.org, mtosatti@...hat.com,
	Yang Zhang <yang.z.zhang@...el.com>
Subject: Re: [v2 resend] kvm/fpu: Enable eager restore kvm FPU for MPX



On 20/05/2015 22:41, Liang Li wrote:
> The MPX feature requires eager KVM FPU restore support. We have verified
> that MPX cannot work correctly with the current lazy KVM FPU restore
> mechanism. Eager KVM FPU restore should be enabled if the MPX feature is
> exposed to VM.
> 
> Signed-off-by: Liang Li <liang.z.li@...el.com>
> Signed-off-by: Yang Zhang <yang.z.zhang@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 1 +
>  arch/x86/kvm/cpuid.c            | 4 ++++
>  arch/x86/kvm/cpuid.h            | 8 ++++++++
>  arch/x86/kvm/vmx.c              | 5 +++++
>  arch/x86/kvm/x86.c              | 3 ++-
>  5 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e61c3a4..4cb39d4 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -401,6 +401,7 @@ struct kvm_vcpu_arch {
>  	struct kvm_mmu_memory_cache mmu_page_header_cache;
>  
>  	struct fpu guest_fpu;
> +	bool eager_fpu;
>  	u64 xcr0;
>  	u64 guest_supported_xcr0;
>  	u32 guest_xstate_size;
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 59b69f6..5ac5e4d 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -95,6 +95,10 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>  	if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
>  		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
>  
> +	if (guest_cpuid_has_mpx(vcpu))
> +		vcpu->arch.eager_fpu = true;
> +	else
> +		vcpu->arch.eager_fpu = false;
>  	/*
>  	 * The existing code assumes virtual address is 48-bit in the canonical
>  	 * address checks; exit if it is ever changed.
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index c3b1ad9..496b369 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -117,4 +117,12 @@ static inline bool guest_cpuid_has_rtm(struct kvm_vcpu *vcpu)
>  	best = kvm_find_cpuid_entry(vcpu, 7, 0);
>  	return best && (best->ebx & bit(X86_FEATURE_RTM));
>  }
> +
> +static inline bool guest_cpuid_has_mpx(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm_cpuid_entry2 *best;
> +
> +	best = kvm_find_cpuid_entry(vcpu, 7, 0);
> +	return best && (best->ebx & bit(X86_FEATURE_MPX));
> +}
>  #endif
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index f7b6168..7082151 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -8445,6 +8445,11 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  			goto free_vmcs;
>  	}
>  
> +	/*
> +	 * activate fpu here is okay, because it will be deactivated soon if the
> +	 * lazy fpu restore mode is used.
> +	 */
> +	vmx_fpu_activate(&vmx->vcpu);
>  	return &vmx->vcpu;
>  
>  free_vmcs:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5f38188..4d9f8e9 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7060,7 +7060,8 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
>  	fpu_save_init(&vcpu->arch.guest_fpu);
>  	__kernel_fpu_end();
>  	++vcpu->stat.fpu_reload;
> -	kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
> +	if (!vcpu->arch.eager_fpu)
> +		kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
>  	trace_kvm_fpu(0);
>  }
>  
> 

Thanks, applied to kvm/master.

Paolo
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