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

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  Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support "Michael J. Redd" <micredd@gmail.com> - 2018-01-19 01:40 +0100
    Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support Hans van Kranenburg <hans@knorrie.org> - 2018-01-19 22:50 +0100
      Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support "Michael J. Redd" <micredd@gmail.com> - 2018-01-20 19:20 +0100
    Processed (with 1 error): Re: Bug#887676: Stretch kernel  4.9.0-5-amd64 breaks Xen PVH support "Debian Bug Tracking System" <owner@bugs.debian.org> - 2018-01-19 22:50 +0100

#60023 — Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support

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)

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#60026

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

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#60031

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

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#60027 — Processed (with 1 error): Re: Bug#887676: Stretch kernel 4.9.0-5-amd64 breaks Xen PVH support

Processing control commands:

> forcemerge 886591 -1
Bug #886591 [src:linux] 4.9.0-5 (after kaiser patch) breaks xen pvh
Bug #886491 [src:linux] linux-image-4.9.0-5-amd64: Does not boot as Xen guest in PVH mode
Unable to merge bugs because:
package of #887676 is 'linux-image-amd64' not 'src:linux'
Failed to forcibly merge 886591: Did not alter merged bugs.


-- 
886491: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=886491
886591: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=886591
887676: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=887676
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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