linux-kernel - RE: [PATCH] kvm/fpu: Enable eager restore kvm FPU for MPX

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Date:	Wed, 20 May 2015 05:20:57 +0000
From:	"Zhang, Yang Z" <yang.z.zhang@...el.com>
To:	"Li, Liang Z" <liang.z.li@...el.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"gleb@...nel.or" <gleb@...nel.or>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH] kvm/fpu: Enable eager restore kvm FPU for MPX

Li, Liang Z wrote on 2015-05-20:
> 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>
> ---
>  arch/x86/kvm/vmx.c | 2 ++
>  arch/x86/kvm/x86.c | 3 ++-
>  2 files changed, 4 insertions(+), 1 deletion(-)
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index
> f7b6168..e2cccbe 100644 --- a/arch/x86/kvm/vmx.c +++
> b/arch/x86/kvm/vmx.c @@ -8445,6 +8445,8 @@ static struct kvm_vcpu
> *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  			goto free_vmcs;
>  	}
> +	if (vmx_mpx_supported())

Is it better to use guest_cpuid_has_mpx() instead of vmx_mpx_supported()?

> +		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..5993f5f 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 (!kvm_x86_ops->mpx_supported())
> +		kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
>  	trace_kvm_fpu(0);
>  }


Best regards,
Yang


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