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

[Andre Przywara]

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@xxxxxxx>
> > >
> > > 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@xxxxxxx>
> > > Cc: Andreas Herrmann<andreas.herrmann3@xxxxxxx>
> > > Cc: stable@xxxxxxxxxxxxxxx # 3.4+
> > > Link:<http://lkml.kernel.org/r/1338383402-3838-1-git-send-email-andre.przywara@xxxxxxx>
> > > [Boris: correct and expand commit message]
> > > Signed-off-by: Borislav Petkov<borislav.petkov@xxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxxxxxx>
To: <linux-kernel@xxxxxxxxxxxxxxx>, <stable@xxxxxxxxxxxxxxx>
CC: <torvalds@xxxxxxxxxxxxxxxxxxxx>, <akpm@xxxxxxxxxxxxxxxxxxxx>, 
<alan@xxxxxxxxxxxxxxxxxxx>, Andre Przywara <andre.przywara@xxxxxxx>, "H. 
Peter Anvin" <hpa@xxxxxxxxx>

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

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

From: Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>

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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