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 10:18:56 +0200
From:	Andre Przywara <andre.przywara@....com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	Borislav Petkov <bp@...64.org>, "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 10:08 AM, Greg KH wrote:
> On Thu, Jun 07, 2012 at 09:49:01AM +0200, Andre Przywara wrote:
>> 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.
>
> What?  So I don't need to do anything?
>
> Totally confused,

Sorry for that.

To fix the issue, we need only one of those patches.
Mine ("Fix crash as Xen Dom0 on AMD Trinity systems", removing "_amd" 
from the rd/wrmsr calls) was sent out earlier, so I added the stable tag.
A bit later Konrad sent his patch (1ab46fd319bc, initializing the 
forgotten PVOPS members), which hpa took (dropping mine). So this fix is 
in 3.5-rc1 and should also be in -stable.
Now for making things smoother Boris sent out mine again - for 3.6 - and 
more or less accidentally kept the stable tag in it.

Long story short: everything is fine, just apply the one you sent the 
review message for.

HTH,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany

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