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Date: Tue, 3 Mar 2015 19:15:42 +0100
From: "Luis R. Rodriguez" <mcgrof@suse.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        xen-devel@lists.xenproject.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Andrey Ryabinin <a.ryabinin@samsung.com>
Subject: Re: [Xen-devel] [PATCH] x86/xen: Initialize cr4 shadow for 64-bit
	PV(H) guests
Message-ID: <20150303181542.GZ8749@wotan.suse.de>
References: <1424707260-4302-1-git-send-email-boris.ostrovsky@oracle.com> <54EB5EC7.2020300@citrix.com> <CAB=NE6V6K-OceG8Vw6Zhh6JuCCxNN=R5AWHjjduv-s6qQnB5MQ@mail.gmail.com> <54F5C4D6.9010907@oracle.com>
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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@citrix.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