linux-kernel - Re: [PATCH 1/2] KVM: x86: disable MPX if host did not enable MPX XSAVE features

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Message-ID: <56F3E6AB.5070902@redhat.com>
Date:	Thu, 24 Mar 2016 14:07:55 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Yang Zhang <yang.zhang.wz@...il.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: Re: [PATCH 1/2] KVM: x86: disable MPX if host did not enable MPX
 XSAVE features



On 24/03/2016 14:06, Yang Zhang wrote:
> 
> I mean why not keep the old way that only activate the eager_fpu while
> guest sees the MPX bit in CPUID, like:
> 
> vcpu->arch.eager_fpu = use_eager_fpu() && guest_cpuid_has_mpx(vcpu);

If the host uses eager FPU you can assume that it's faster than lazy FPU.

Paolo

> Besides, vmx_fpu_activate is called when do vcpu_reset. So it seems no
> need to call fpu_activate() here again.