On 2016/3/11 20:09, Paolo Bonzini wrote:
Sorry for the late reply.
On 11/03/2016 03:37, Yang Zhang wrote:
@@ -97,7 +104,7 @@ 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);
- vcpu->arch.eager_fpu = use_eager_fpu() || guest_cpuid_has_mpx(vcpu);
+ vcpu->arch.eager_fpu = use_eager_fpu();
Hi Paolo,
As i mentioned on another thread, force KVM to use eager fpu
unconditionally may introduce the performance regression. Though the
cost for eager fpu is very small especially in modern CPU, it still
cannot be ignored on old platform.
This patch doesn't change anything in that respect. It doesn't enable
eager FPU in any case where it wasn't already enabled before the patch.
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);
Besides, vmx_fpu_activate is called when do vcpu_reset. So it seems no
need to call fpu_activate() here again.
--
best regards
yang
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