Re: Problems with APIC on versions 4.9 and later (4.8 works)

[Jan Beulich <jbeulich@xxxxxxxx>]

On 29.01.2021 20:31, Claudemir Todo Bom wrote:
> Em sex., 29 de jan. de 2021 às 13:24, Jan Beulich <jbeulich@xxxxxxxx> 
> escreveu:
>>
>> On 28.01.2021 14:08, Claudemir Todo Bom wrote:
>>> Em qui., 28 de jan. de 2021 às 06:49, Jan Beulich <jbeulich@xxxxxxxx> 
>>> escreveu:
>>>>
>>>> On 28.01.2021 10:47, Jan Beulich wrote:
>>>>> On 26.01.2021 14:03, Claudemir Todo Bom wrote:
>>>>>> If this information is good for more tests, please send the patch and
>>>>>> I will test it!
>>>>>
>>>>> Here you go. For simplifying analysis it may be helpful if you
>>>>> could limit the number of CPUs in use, e.g. by "maxcpus=4" or
>>>>> at least "smt=0". Provided the problem still reproduces with
>>>>> such options, of course.
>>>>
>>>> Speaking of command line options - it doesn't look like you have
>>>> told us what else you have on the Xen command line, and without
>>>> a serial log this isn't visible (e.g. in your video).
>>>
>>> All tests are done with xen command line:
>>>
>>> dom0_mem=1024M,max:2048M dom0_max_vcpus=4 dom0_vcpus_pin=true
>>> smt=false vga=text-80x50,keep
>>>
>>> and kernel command line:
>>>
>>> loglevel=0 earlyprintk=xen nomodeset
>>>
>>> this way I can get all xen messages on console.
>>>
>>> Attached are the frames I captured from a video, I manually selected
>>> them starting from the first readable frame.
>>
>> I've just sent a pair of patches, with you Cc-ed on the 2nd one.
>> Please give that one a try, with or without the updated debugging
>> patch below. In case of problems I'd of course want to see the
>> output from the debugging patch as well. I think it's up to you
>> whether you also use the first patch from that series - afaict it
>> shouldn't directly affect your case, but I may be wrong.
> 
> I've applied both patches, system didn't booted, used following parameters:
> 
> xen: dom0_mem=1024M,max:2048M dom0_max_vcpus=4 dom0_vcpus_pin=true smt=true
> kernel: loglevel=3
> 
> The screen cleared right after the initial xen messages and frozen
> there for a few minutes until I restarted the system.
> 
> I've added "vga=text-80x25,keep" to the xen command line and
> "nomodeset" to the kernel command line, hoping to get some more info
> and surprisingly this was sufficient to make system boot!

Odd, but as per my reply to the patch submission itself a
few minutes ago, over the weekend I realized a flaw. I do
think this explains the anomalies seen from the log between
CPU0 and and all other CPUs; the problem merely isn't as
severe anymore as it was before as it seems. I also did
realize I ought to be able to mimic your system's behavior;
if so I ought to be able to send out an updated series that
actually had some testing for the specific case. Later
today, hopefully.

Jan