[Pkg-xen-devel] Dom0 on Sid not working

[Chuck Zmudzinski]

On 4/23/22 6:03 PM, Marek Marczykowski-Górecki wrote:
> On Sat, Apr 23, 2022 at 12:42:36PM -0400, Chuck Zmudzinski wrote:
>> Hello,
>>
>> After updating Sid this morning, which included an upgrade to Linux kernel
>> version 5.17.x from 5.16.x, the system will not boot into Dom0 on Xen.
>>
>> Package versions:
>>
>> Xen hypervisor: xen-hypervisor-4.16-amd64 Debian version
>> 16.0+51-g0941d6cb-1+b1
>> Linux kernel in Dom0: linux-image-5.17.0-1-amd64 Debian version 5.17.3-1
>>
>> The system boots into Linux 5.17.3-1 fine on the bare metal, but not as Dom0
>> on the Xen 4.16 hypervisor Debian version 16.0+51-g0941d6cb-1+b1
>>
>> The system never shows boot messages or a login prompt, but the monitor
>> stays powered on but with no text or image at all. It seems to just hang
>> indefinitely. Downgrading to the latest 5.16 kernel on Xen 4.16 Debian
>> version 16.0+51-g0941d6cb-1+b1 works normally. Anybody else see this
>> problem?
> We have similar issue in Qubes OS:
> https://github.com/QubesOS/qubes-issues/issues/7462. Are you running
> this on AMD?
>

Hi Marek,

I found a fix for my Intel system. The offending commit which
is in Linux 5.17 but not 5.16:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bdd8b6c98239cad3a976d6f197afc2c794d3cef8

Jan Beulich posted a patch to fix this, and I tested it and it fixed
my system, but it is not yet committed to Linux:

https://lore.kernel.org/lkml/9385fa60-fa5d-f559-a137-6608408f88b0@suse.com/

Although the offending commit only affects Intel drivers, the fix
is in the underlying pat_enabled() function which provides a false
negative when device drivers test for the X86 PAT feature if
Linux is running on the Xen hypervisor. If one of your AMD device
drivers is also relying on pat_enabled() to test for the X86 PAT 
feature, Jan's patch might fix the problem on your AMD system.

Best regards,

Chuck