Re: [Xen-devel] dom0pvh issue with XEN 4.8.0

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Feb 06, 2017 at 06:25:57PM +0800, G.R. wrote:
> On Mon, Feb 6, 2017 at 5:33 PM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> > Hi,
> >
> > On Sun, Feb 05, 2017 at 04:05:32PM +0800, G.R. wrote:
> >> Hi all,
> >> dom0pvh=1 is not working well for me with XEN 4.8.0 + linux kernel 4.9.2.
> >>
> >> The system boots with no obvious issue.
> >> But many user mode application are suffering from segfault, which
> >> makes the dom0 not useable: The segfault always come from libc-2.24.so
> >> while it works just fine in PV dom0.
> >> I have no idea why, but those segfault would kill my ssh connection
> >> while sshd is not showing up in the victim list.
> >>
> >> Some examples:
> >> Feb  5 14:25:28 gaia kernel: [  123.446346] getty[3044]: segfault at 0
> >> ip 00007f5e769e6c60 sp 00007ffc57bc0a98 error 6 in
> >> libc-2.24.so[7f5e769b7000+195000]
> >> Feb  5 14:29:04 gaia kernel: [  339.671742] grep[4195]: segfault at 0
> >> ip 00007f5d3b95ac60 sp 00007ffcc1620bb8 error 6 in
> >> libc-2.24.so[7f5d3b92b000+195000]
> >> Feb  5 14:29:23 gaia kernel: [  358.495888] tail[4203]: segfault at 0
> >> ip 00007f751314bc60 sp 00007fffe5ce5e48 error 6 in
> >> libc-2.24.so[7f751311c000+195000]
> >> Feb  5 14:35:06 gaia kernel: [  701.314247] bash[4323]: segfault at 0
> >> ip 00007f3fef30ec60 sp 00007ffd48cc2058 error 6 in
> >> libc-2.24.so[7f3fef2df000+195000]
> >> Feb  5 14:48:43 gaia kernel: [ 1518.809924] ls[4910]: segfault at 0 ip
> >> 00007f29e9bc1c60 sp 00007ffd712752b8 error 6 in
> >> libc-2.24.so[7f29e9b92000+195000]
> >>
> >> Any suggestion on how to get this fixed?
> >> I don't think I can do live debug since the userspace is quite unstable.
> >> On the other hand, dmesg from both dom0 && XEN looks just fine.
> >>
> >> PS: I'm using a custom compiled dom0 kernel. Is there any specific
> >> kernel config is required to get dom0pvh=1 work?
> >>
> >
> > I think the plan is to replace/rewrite the PVH (dom0) support with PVHv2,
> > see Roger's recent series here on xen-devel mailinglist..
> >
> 
> Thanks for all your input.
> Just had another check on the feature sheet, really didn't notice that
> PVH is still an 'preview' feature.
> Had the wrong impression since the feature had been announced for 2~3
> years anyway.
> Will avoid this for the moment.

Hello,

Yes, it's best to avoid it for the time being, but I'm still concerned by this.
The classic PVH mode is used by FreeBSD, and I have never received any reports
of SEGFAULTs in user-space applications, so it looks like an issue on the Linux
kernel and not Xen itself.

Roger.

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