[Pkg-xen-devel] Bug#1020787: linux-image-5.19.0-2-amd64: After updating to 5.19 kernel the VMs are started without XSAVE CPU flags

[Diederik de Haas]

Control: tag -1 moreinfo

On Monday, 26 September 2022 20:04:10 CEST patrick wrote:
> I have a XEN hypervisor running with some VMs (everything based on Debian).

Which version of Xen are you using?

> After updating to the Kernel to 5.19 (from 5.18.0-4), some binaries are
> falling to execute. If the VMs are started with Kernel 5.18.0-4 they are
> running fine.

Is this all about the dom0 kernel or is it all/some about using 5.19 as 
domU kernel? Are the issues happing on dom0 or inside domU?

If the issues happen inside (a) domU, can you share a (minimal) domU 
configuration file so it becomes easier to replicate?

> And indeed there is some difference in /proc/cpuinfo:
> The flags for "fma xsave avx2 bmi2 xsaveopt xsavec xgetbv1 md_clear" are
> missing, which might result in gnutls failures.

In kernel 5.19 the following commits were added under ``arch/x86/kernel/fpu/``:

b91c0922bf1ed15b67a6faa404bc64e3ed532ec2 x86/fpu: Cleanup variable shadowing
8ad7e8f696951f192c6629a0cbda9ac94c773159 x86/fpu/xsave: Support XSAVEC in the kernel
f5c0b4f30416c670408a77be94703d04d22b57df x86/prctl: Remove pointless task argument

Of these, the first 2 seem like possible candidates that caused the issue.
https://kernel-team.pages.debian.net/kernel-handbook/ch-common-tasks.html#s4.2.2
describes a way to apply a simple patch to a kernel.
What you could try, is creating a patch from reverting one of the earlier
mentioned commits and use that with 'test-patches'.

It's probably also useful to know what CPU(s) are in the machine (dom0).

On Monday, 26 September 2022 20:31:17 CEST Ps Ps wrote:
> On Xen Hypervisor I just found this logs:

So this is on dom0? In which log file did you find it?

Generally: be as specific as you can be and describe *exactly* what you did
and the exact results (if any). Also try to make it as easy as possible for
others to reproduce what you're experiencing.

FTR: I did not see this issue on my dom0 (Xen 4.16.2-1; kernel 5.19.11-1):

root at dom0:~# dmesg
[    0.000000] Linux version 5.19.0-2-amd64 (debian-kernel at lists.debian.org) (gcc-11 (Debian 11.3.0-6) 11.3.0, GNU ld (GNU Binutils for Debian) 2.38.90.20220713) #1 SMP PREEMPT_DYNAMIC Debian 5.19.11-1 (2022-09-24)
[    0.000000] Command line: placeholder root=UUID=8008723b-668f-43f6-b432-8c56ed53f48a ro quiet net.ifnames=0
[    0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers'
[    0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers'
[    0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers'
[    0.000000] x86/fpu: xstate_offset[2]:  576, xstate_sizes[2]:  256
[    0.000000] x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format.
[    0.000000] signal: max sigframe size: 1776
[    0.000000] Released 0 page(s)

root at dom0:~# grep flag /proc/cpuinfo | uniq
flags           : fpu de tsc msr pae mce cx8 apic sep mca cmov pat clflush acpi mmx fxsr sse sse2 ss ht syscall nx rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid tsc_known_freq pni pclmulqdq monitor est ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand hypervisor lahf_lm abm 3dnowprefetch cpuid_fault ssbd ibrs ibpb stibp fsgsbase bmi1 avx2 bmi2 erms rtm rdseed adx xsaveopt md_clear


Also found this patch which should make the error msg more informative ...
https://lore.kernel.org/all/20220810221909.12768-1-andrew.cooper3@citrix.com/
Even though I haven't experienced it (yet?), the language of this patch
seems to indicate you're not alone with it.
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