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Re: early crash while loading dom0 kernel between git:19730dbb3f and git:414dde38b0


  • To: "Greg A. Woods" <woods.greg.a@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 17 Feb 2025 22:10:32 +0000
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • Delivery-date: Mon, 17 Feb 2025 22:10:45 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 17/02/2025 10:02 pm, Greg A. Woods wrote:
> A quick reply, maybe more later...
>
> I thought I had done a fresh clean build as I ran "gmake clean" in the top
> level directory, however then when reading your's and Andrew's replies I
> realized I have been doing the Xen kernel build in a separate build directory,
> which the top-level makefile won't know about.  (I never build in the source
> tree of anything if at all possible.)
>
> So I cleaned everything out and started again, and voila!  It works!
>
> This is definitely annoying, but not a deal breaker!

Glad it's not a *different* weird breakage.  And at least now we've got
a stated repro of the issue.

> Note again my local patches do not change any actual code in the xen subdir.
>
> The "has no endbr64" messages are possibly due to the fact that I'm still
> using GCC-9.x on NetBSD, and as I understand it that compiler is too old
> to support ENDBR instructions.  I disabled the related build-time tests.
> I can build with GCC-10.5 on another host and try that too.

Can you attach your .config file from the build?  Those messages ought
to only show up in builds where ENDBR's are present, but it's possible
that something's out of sync with the various Kconfig controls involved.

> BTW, there is also another regression (since 4.13, I think) on some hardware
> that I've been trying to gather more data on, thus my testing from git.  That
> is that on two of my older machines both the dom0 and domUs (running NetBSD
> and FreeBSD) lose track of time after about 7.5 days.  The same code on a
> slightly newer server runs reliably with accurate time.  Others using NetBSD
> on Xen have reported similar problems.  Some claim running with 1 vCPU avoids
> the problem.  I'm guessing something in the Xen kernel loses track of TSC
> scaling when running on some CPUs.  This has been discussed in the port-xen
> list for the past few months:  https://mail-index.netbsd.org/port-xen/

Time handling is a known swamp.  I can believe something has changed
since 4.13, but I wouldn't say it was working back then either.

~Andrew



 


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