Paolo Bonzini wrote on 2015-05-20: > > > On 20/05/2015 07:20, Zhang, Yang Z wrote: >> 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@xxxxxxxxx> >>> --- >>> 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()) >>> + vmx_fpu_activate(&vmx->vcpu); >>> return &vmx->vcpu; >>> >>> free_vmcs: >> >> Is it better to use guest_cpuid_has_mpx() instead of vmx_mpx_supported()? > > CPUID hasn't been set yet, so I think it is okay to key it on > vmx_mpx_supported(). It will be deactivated soon afterwards. > > Or even do it unconditionally; just make sure to add a comment about it. Correct! Unconditionally would be acceptable. > >>> 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); >>> } > > This is a hotter path. Here it's definitely better to avoid the call > to kvm_x86_ops->mpx_supported(). Especially because, with MPX > enabled, you would call this on every userspace exit. > > Yang's suggestion of using CPUID is actually more valuable here. You > could add a new field eager_fpu in kvm->arch and update it in kvm_update_cpuid. Good suggestion! > > Thanks, > > Paolo Best regards, Yang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
