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

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Date:	Mon, 24 Feb 2014 12:13:13 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>,
	"'kvm@...r.kernel.org'" <kvm@...r.kernel.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'qemu-devel@...gnu.org'" <qemu-devel@...gnu.org>
CC:	"'gleb@...hat.com'" <gleb@...hat.com>,
	"'hpa@...or.com'" <hpa@...or.com>
Subject: Re: [PATCH v5 3/3] KVM: x86: Enable Intel MPX for guest

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
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