lkml.org 
[lkml]   [2016]   [Apr]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH 1/2] KVM: x86: disable MPX if host did not enable MPX XSAVE features
From
Date
On 2016/3/24 21:07, Paolo Bonzini wrote:
>
>
> 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.

Hi Paolo

The check in kvm_update_cpuid of fpu is strange since nothing relies on
cpuid now. How about the following change?

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index bbbaa80..da4e6ad 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -114,9 +114,6 @@ 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 (use_eager_fpu())
- kvm_x86_ops->fpu_activate(vcpu);
-
/*
* 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/x86.c b/arch/x86/kvm/x86.c
index 9b7798c..8f57335 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7453,6 +7453,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool
init_event)
vcpu->arch.regs_avail = ~0;
vcpu->arch.regs_dirty = ~0;

+ if (use_eager_fpu())
+ kvm_x86_ops->fpu_activate(vcpu);
+
kvm_x86_ops->vcpu_reset(vcpu, init_event);
}

--
best regards
yang

\
 
 \ /
  Last update: 2016-04-13 12:01    [W:0.061 / U:1.076 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site