Re: [Xen-devel] Debugging Windows HVM crashes on Ryzen 3xxx series CPUs.

From: Paul Durrant <pdurrant@gmail.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Juergen Gross <JGross@suse.com>,
	Lars Kurth <lars.kurth@citrix.com>,
	Steven Haigh <netwiz@crc.id.au>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [Xen-devel] Debugging Windows HVM crashes on Ryzen 3xxx series CPUs.
Date: Mon, 28 Oct 2019 10:42:01 +0000	[thread overview]
Message-ID: <CACCGGhDpfQmg9es=yTiSDPuSaGW1W8wKJ0-hsTrhHx2_7MjSTQ@mail.gmail.com> (raw)
In-Reply-To: <7333496f-48e7-c659-5314-54feffde0273@suse.com>

On Mon, 28 Oct 2019 at 09:21, Jan Beulich <jbeulich@suse.com> wrote:
>
> On 25.10.2019 19:01, Andrew Cooper wrote:
> > On 24/10/2019 12:57, Steven Haigh wrote:
> >> Hi all,
> >>
> >> I've managed to get the git master version of Xen on this affected
> >> system and tries to boot a Windows Server 2016 system. It crashes as
> >> per normal.
> >>
> >> I managed to get these logs, but I'm not quite sure what else to do to
> >> debug this issue further.
> >
> > After a collaborative debugging session on IRC, we've identified the
> > problem.  Here is a summary.
> >
> > https://www.reddit.com/r/Amd/comments/ckr5f4/amd_ryzen_3000_series_linux_support_and/
> > is concerning KVM, but it identified that the TOPOEXT feature was
> > important to getting windows to boot.
> >
> > Xen doesn't currently offer TOPOEXT to guests at all.  Fixing this is on
> > the TODO list along with the rest of the topology representation swamp.
> >
> > On a hunch, I offered up a XenServer patch which we are still using, in
> > lieu of fixing topology properly.  It is logically a revert of
> > ca2eee92df44 as that change wasn't migration safe.
>
> Would you mind helping me understand how this revert matches up with
> you saying above that TOPOEXT is needed for Windows to boot here? I
> don't think I can conclude anything in this direction from the article
> you've provided the link of.
>

No, I couldn't quite see that. Google found me
https://lists.gnu.org/archive/html/qemu-devel/2018-03/msg03684.html
which suggests that topoext deals with cache topology information,
rather than being to do with cores/threads. Is Windows simply assuming
the existence of the info. because it is seeing the model/family of
the physical CPU and then getting upset because it's not there?

  Paul

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