Re: [Qemu-devel] [PATCH v5 3/3] KVM: x86: Enable Intel MPX for guest

[Paolo Bonzini]

Il 24/02/2014 11:58, Liu, Jinsong ha scritto:
> @@ -599,6 +599,9 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
>         u64 old_xcr0 = vcpu->arch.xcr0;
>         u64 valid_bits;
>
> +       if (!kvm_x86_ops->mpx_supported || !kvm_x86_ops->mpx_supported())
> +               xcr0 &= ~(XSTATE_BNDREGS | XSTATE_BNDCSR);
> +
>         /* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now  */
>         if (index != XCR_XFEATURE_ENABLED_MASK)
>                 return 1;

This hunk is incorrect, and I can simply drop it when applying.  If MPX 
is not supported, it should not be in the 0Dh CPUID leaf and thus in 
vcpu->arch.guest_supported_xcr0.

This however relies on userspace passing a "sensible" value of CPUID. 
I'll send a patch to strengthen the computation of guest_supported_xcr0.

Thanks!

Paolo