Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support

[Michael J. Redd]

Aha! Okay, that certainly explains some things. I didn't realize PVH
was a "use at your own risk" tech preview in Xen 4.8 and kernel 4.9.
Luckily, my infrastructure didn't rely on PVH to start with; I can go
back to conventional PV or HVM with no problem.

Thanks for investigating!

-Michael

Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support

[Hans van Kranenburg]

Control: forcemerge 886591 -1

Hi,

On 01/19/2018 01:30 AM, Michael J. Redd wrote:
> Package: linux-image-amd64
> Version: 4.9+80+deb9u
> 
> [...]
> 
> Latest Stretch kernel (4.9.0-5-amd64), released per DSA-4082-1, breaks
> Xen PVH domU support.

If you are using Xen 4.8, then it's the obsolete PVH v1.

Sorry to be the one that has to make your day miserable, but PVH was not
supposed to be used by end users and not supported in any way before Xen
4.10 and Linux kernel 4.11 in the guest.

That means, there is no solution for this and there will not be.

https://lists.xenproject.org/archives/html/xen-devel/2018-01/msg00540.html

Hans

Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support

[Michael J. Redd]

Package: linux-image-amd64
Version: 4.9+80+deb9u

Not sure if this needs to go to the Debian Kernel team or Debian Xen
team, so please feel free to reclassify as necessary. I'm leaning
toward this being a kernel bug, as the Xen packages had not changed
when this issue was introduced; only the kernel changed.

Description:


Latest Stretch kernel (4.9.0-5-amd64), released per DSA-4082-1, breaks
Xen PVH domU support. Booting the domU with pvh = '1' set in its config
file gets the boot process as far as pyGRUB, but once the kernel itself
begins to boot, the domU immediately crashes. Even with 'quiet' removed
from the kernel's boot options, the kernel outputs nothing before it
dies.

Thinking this was possibly the work of the Meltdown mitigation, I added
`pti=off` to the domU's kernel boot options. No effect.

Steps to reproduce:
===

1. Run Xen PV domU in PVH mode (PVH = '1' in domU config file),
2. Upgrade domU's kernel from 4.9.0-4-amd64 to 4.9.0-5-amd64,
3. Reboot domU using latest kernel.

Workaround:
===

I could find no workaround with this kernel. I either had to disable
Xen PVH mode (set PVH = '0') for the domU or roll back to using kernel
4.9.0-4-amd64.

Setup:
==

- Dom0 kernel: 4.9.0-5-amd64
- DomU kernel: 4.9.0-5-amd64
- Xen hypervisor version: xen-hypervisor-4.8-amd64 (4.8.2+xsa245-
0+deb9u1)