linux-kernel - Re: [PATCH 3/4] x86, AMD: Fix crash as Xen Dom0 on AMD Trinity systems

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Date:	Thu, 7 Jun 2012 09:49:01 +0200
From:	Andre Przywara <andre.przywara@....com>
To:	Borislav Petkov <bp@...64.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jacob Shin <jacob.shin@....com>, <jeremy@...p.org>,
	<xen-devel@...ts.xensource.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...e.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH 3/4] x86, AMD: Fix crash as Xen Dom0 on AMD Trinity systems

On 06/07/2012 09:21 AM, Borislav Petkov wrote:
> On Wed, Jun 06, 2012 at 03:00:14PM -0700, H. Peter Anvin wrote:
>> On 06/01/2012 07:52 AM, Borislav Petkov wrote:
>>> From: Andre Przywara<andre.przywara@....com>
>>>
>>> f7f286a910221 ("x86/amd: Re-enable CPU topology extensions in case BIOS
>>> has disabled it") wrongfully added code which used the AMD-specific
>>> {rd,wr}msr variants for no real reason.
>>>
>>> This caused boot panics on xen which wasn't initializing the
>>> {rd,wr}msr_safe_regs pv_ops members properly.
>>>
>>> This, in turn, caused a heated discussion leading to us reviewing all
>>> uses of the AMD-specific variants and removing them where unneeded
>>> (almost everywhere except an obscure K8 BIOS fix, see 6b0f43ddfa358).
>>>
>>> Finally, this patch switches to the standard {rd,wr}msr*_safe* variants
>>> which should've been used in the first place anyway and avoided unneeded
>>> excitation with xen.
>>>
>>> Signed-off-by: Andre Przywara<andre.przywara@....com>
>>> Cc: Andreas Herrmann<andreas.herrmann3@....com>
>>> Cc: stable@...r.kernel.org # 3.4+
>>> Link:<http://lkml.kernel.org/r/1338383402-3838-1-git-send-email-andre.przywara@amd.com>
>>> [Boris: correct and expand commit message]
>>> Signed-off-by: Borislav Petkov<borislav.petkov@....com>
>>
>> Why -stable?  I though we had agreed that we didn't have an active
>> problem (unclean hack, yes, but not an active problem) in 3.4/3.5 as it
>> currently sits?

This is probably a leftover from the original patch, before Konrad's 
patch got committed.

> Yes, AFAICT, we need at least one fix for 3.4 where the original patch
> f7f286a910221 broke xen.
>
> So either this one or 1ab46fd319bc should be backported to stable, if
> I'm not mistaken. If the second, I'll drop the stable tag from this one
> and resend.
>
> Konrad, what do you want wrt xen paravirt nullptr breakage for
> 3.4-stable?

Greg just sent out the review mail for 1ab46fd319bc, so we can drop the 
stable tag from this one.

Regards,
Andre.

-------- Original Message --------
Subject: [ 21/82] x86, amd, xen: Avoid NULL pointer paravirt references
Date: Thu, 7 Jun 2012 13:03:57 +0900
From: Greg KH <gregkh@...uxfoundation.org>
To: <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
CC: <torvalds@...ux-foundation.org>, <akpm@...ux-foundation.org>, 
<alan@...rguk.ukuu.org.uk>, Andre Przywara <andre.przywara@....com>, "H. 
Peter Anvin" <hpa@...or.com>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konrad Rzeszutek Wilk <konrad@...nok.org>

commit 1ab46fd319bcf1fcd9fb6311727d532b580e4eba upstream.

Stub out MSR methods that aren't actually needed.  This fixes a crash
as Xen Dom0 on AMD Trinity systems.  A bigger patch should be added to
remove the paravirt machinery completely for the methods which
apparently have no users!
.....



-- 
Andre Przywara
AMD-OSRC (Dresden)
Tel: x29712

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