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

[Marek Marczykowski-Górecki]

On Sat, May 21, 2022 at 11:15:39AM -0400, Chuck Zmudzinski wrote:
> 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/

Thanks for the heads up, I have this patch included already:
https://github.com/QubesOS/qubes-linux-kernel/commit/291aaa58065f061dd6e205354d9f88f39912551d

And indeed it fixes the Intel-related issue with 5.17.

> 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.

I asked the user to try the updated kernel, we'll see.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
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