Re: Linux 5.13+ as Xen dom0 crashes on Ryzen CPU (ucode loading related?)

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.09.2021 09:14, Juergen Gross wrote:
> On 13.09.21 14:50, Marek Marczykowski-Górecki wrote:
>> Hi,
>>
>> Since 5.13, the Xen (PV) dom0 crashes on boot, before even printing the
>> kernel version.
>> Test environment:
>>   - Xen 4.14.2
>>   - AMD Ryzen 5 4500U (reported also on AMD Ryzen 7 4750U)
>>   - Linux 5.13.13, confirmed also on 5.14
>>
>> The crash happens only if the initramfs has earlycpio with microcode.
>> I don't have a serial console, but I've got a photo with crash message
>> (from Xen, Linux doesn't managed to print anything):
>> https://user-images.githubusercontent.com/726704/133084966-5038f37e-001b-4688-9f90-83d09be3dc2d.jpg
>>
>> Transcription of some of it:
>>
>>      mapping kernel into physical memory
>>      about to get started
>>      (XEN) Pagetable walk from ffffffff82810888:
>>      (XEN)  L4[0x1ff] = 0000000332815067 0000000000002815
>>      (XEN)  L3[0x1fe] = 0000000332816067 0000000000002816
>>      (XEN)  L2[0x014] = 0000000334018067 0000000000004018
>>      (XEN)  L1[0x010] = 0000000332810067 0000000000002810
>>      (XEN) domain_crash_sync called from entry.S: fault at ffff82d04033e790 
>> x86_64/entry.S#domain_crash_page_fault
>>      (XEN) Domain 0 (vcpu#0) crashed on cpu#0:
>>      (XEN) ----[ Xen-4.14.2  x86_64  debug=n  Not tainted ]----
>>      (XEN) CPU:    0
>>      (XEN) RIP:    e033:[<0000000000000000>]
> 
> The domain's run state seems to be completely clobbered.
> 
> Did you try to boot the kernel with "earlyprintk=xen" to get some idea
> how far it progressed?

I guess without my "xen/x86: allow "earlyprintk=xen" to work for PV Dom0"
"earlyprintk=xen" would need to be accompanied by "console=xenboot". I
have not tried whether this helps, this is merely a guess from having
looked at the code relatively recently.

Jan