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

[Andre Przywara <andre.przywara@xxxxxxx>]

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@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.
> 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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