linux-kernel - Re: [Xen-devel] PROBLEM: kernel panic xsave

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Date:	Tue, 20 Oct 2015 10:27:41 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Jan Beulich <JBeulich@...e.com>, John Doe <securef33d@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, x86@...nel.org,
	xen-devel@...ts.xen.org, linux-kernel@...r.kernel.org
Subject: Re: [Xen-devel] PROBLEM: kernel panic xsave_init

On 10/20/2015 09:43 AM, Jan Beulich wrote:
>>>> On 20.10.15 at 15:22, <boris.ostrovsky@...cle.com> wrote:
>> The reason I think its this commit is that RAX, RDX and RCX look very
>> much like arguments to xsetbv (which xstate_enable_boot_cpu() executes)
>> and RAX value is 0x1f, which has two new bits that this commit defined.
> That would be the two MPX related bits, yet us (luckily) white listing
> leaf 7 in pv_cpuid(), it is quite easy to validate that we don't expose
> this feature to PV(H) guests.

Oh, so something like

cpuid=['0x7:ebx=xxxxxxxxxxxxxxxxx0xxxxxxxxxxxxxx']

(bit 14 as zero) for John to try then.


-boris

> Sadly the story is different for HVM
> guests (where the leaf handling uses black listing), but the register
> dump here clearly points to a PV guest (or Dom0).
>
> Jan
>

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