Re: PV guest with PCI passthrough crash on Xen 4.8.3 inside KVM when booted through OVMF

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Fri, Feb 16, 2018 at 05:52:50PM +0000, Andrew Cooper wrote:
> On 16/02/18 17:48, Marek Marczykowski-Górecki wrote:
> > Hi,
> >
> > As in the subject, the guest crashes on boot, before kernel output
> > anything. I've isolated this to the conditions below:
> >  - PV guest have PCI device assigned (e1000e emulated by QEMU in this case),
> >    without PCI device it works
> >  - Xen (in KVM) is started through OVMF; with seabios it works
> >  - nested HVM is disabled in KVM
> >  - AMD IOMMU emulation is disabled in KVM; when enabled qemu crashes on
> >    boot (looks like qemu bug, unrelated to this one)
> >
> > Version info:
> >  - KVM host: OpenSUSE 42.3, qemu 2.9.1, ovmf-2017+git1492060560.b6d11d7c46-4.1, AMD
> >  - Xen host: Xen 4.8.3, dom0: Linux 4.14.13
> >  - Xen domU: Linux 4.14.13, direct boot
> >
> > Not sure if relevant, but initially I've tried booting xen.efi /mapbs
> > /noexitboot and then dom0 kernel crashed saying something about conflict
> > between e820 and kernel mapping. But now those options are disabled.
> >
> > The crash message:
> > (XEN) d1v0 Unhandled invalid opcode fault/trap [#6, ec=0000]
> > (XEN) domain_crash_sync called from entry.S: fault at ffff82d080218720 entry.o#create_bounce_frame+0x137/0x146
> > (XEN) Domain 1 (vcpu#0) crashed on cpu#1:
> > (XEN) ----[ Xen-4.8.3  x86_64  debug=n   Not tainted ]----
> > (XEN) CPU:    1
> > (XEN) RIP:    e033:[<ffffffff826d9156>]
> 
> This is #UD, which is most probably hitting a BUG().  addr2line this ^
> to find some code to look at.

addr2line failed me, but System.map says its xen_memory_setup. And it
looks like the BUG() is the same as I had in dom0 before:
"Xen hypervisor allocated kernel memory conflicts with E820 map".

Disabling e820_host in guest config solved the problem. Thanks!

Is this some bug in Xen or OVMF, or is it expected behavior and e820_host
should be avoided?

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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