linux-kernel - Re: [Xen-devel] [PATCH] x86/xen: Initialize cr4 shadow for 64-bit PV(H) guests

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Date:	Tue, 3 Mar 2015 19:15:42 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel@...ts.xenproject.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Andrey Ryabinin <a.ryabinin@...sung.com>
Subject: Re: [Xen-devel] [PATCH] x86/xen: Initialize cr4 shadow for 64-bit
	PV(H) guests

On Tue, Mar 03, 2015 at 09:27:34AM -0500, Boris Ostrovsky wrote:
> On 03/03/2015 12:35 AM, Luis R. Rodriguez wrote:
>> On Mon, Feb 23, 2015 at 9:09 AM, David Vrabel <david.vrabel@...rix.com> wrote:
>>> On 23/02/15 16:01, Boris Ostrovsky wrote:
>>>> Commit 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
>>>> introduced CR4 shadows.
>>>>
>>>> These shadows are initialized in early boot code. The commit missed
>>>> initialization for 64-bit PV(H) guests that this patch adds.
>>> Applied to stable/for-linus-4.0, thanks.
>>>
>>> Boris, can you kick of a set of tests on this branch, please?
>> Do we know worst case what should blow up without this commit ?
>
> PVH guest will crash.

Oh wow that is serious. And this is a reactive measure to a change upstream,
it might be hard but it'd be nice if we can have a proactive architecture
to address this. Don't mind me though, I realize this seems hard, just 
thinking out loud right now. Did you find it through code inspection or
a test?

  Luis
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