On 08/03/2016 10:32, Xiao Guangrong wrote:
> On 03/08/2016 04:47 PM, Paolo Bonzini wrote:
>> Some XSAVE features (currently only MPX, but in the future PKRU too)
>> will force eagerfpu on, see fpu__init_system_ctx_switch:
>>
>> if (xfeatures_mask & XFEATURE_MASK_EAGER) {
>> if (eagerfpu == DISABLE) {
>> xfeatures_mask &= ~XFEATURE_MASK_EAGER;
>
> So if the kernel parameter, eagerfpu is set to "off", then eager is not
> enabled, so PKRU can not work in KVM?
Yes. Neither PKRU nor MPX.
>> KVM will use eager FPU if the host uses it. See arch/x86/kvm/cpuid.c:
>>
>> vcpu->arch.eager_fpu =
>> use_eager_fpu() || guest_cpuid_has_mpx(vcpu);
>>
>
> Sorry, i missread the code, yes, if vcpu->arch.eager_fpu is true, it is
> always save/load fpu for every vm-exit/vm-enter.
No problem, it's impossible to know all the code. :)
Paolo
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