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Re: Segfaults after upgrade to Debian 11.7 on virtualized systems with AMD Ryzen CPU

On 02 May 2023 00:19, NetValue Operations Centre wrote:
Good thinking, trying that.

I worked through some of the cpu features, and when removing the line:

     <feature policy='require' name='pku'/>

the test VM on 5.10.0-22-amd64 booted successfully.


"Memory Protection Keys provides a mechanism for enforcing page-based

"The kernel will send a SIGSEGV in both cases, but si_code will be set
to SEGV_PKERR when violating protection keys versus SEGV_ACCERR when
the plain mprotect() permissions are violated."

So, sounds like a memory protection system which can result in seg faults.

AFAICT the host system is running just fine with PKU feature on hosts running either 5.10.0-21-amd64 or 5.10.0-22-amd64, and the host kernel doesn't seem to affect the guest's behaviour either, only if the guest is running 5.10.0-22-amd64 with PKU passed through.

I don't know the best bug tracker to create a ticket in would be... https://packages.debian.org/bullseye/linux-image-5.10.0-22-amd64 ?


I have a "similar" problem on a Xen dom0, using a Ryzen 1700x.
Xen dom0 won't boot with the new "5.10.0-22-amd64" kernel, but using "5.10.0-21-amd64" works. I don't have a serial console to read the full output, the last visible line is "dom0 has 2 vCPUs". So it happens during the creation of dom0.
With a working kernel (so "5.10.0-21-amd64"), the next lines read:

(XEN) Initial low memory virq threshold set at 0x4000 pages.
(XEN) Scrubbing Free RAM in background

So, as you said, it seems related to some "memory handling/protection system".

But I didn't have any problem updating the Debian domUs to the new kernel, while using the old one in dom0.

PS: if I'm not mistaken, the equivalent of Xen CPU attribution for VMs in KVM is "host-passthrough", maybe try that in your VM configs ?

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