Re: Xen 4.12.0-rc Hangs Around masked ExtINT on CPU#

["John L. Poole" <jlpoole56@gmail.com>]

On 3/27/2019 7:21 AM, Jan Beulich wrote:
>>>> On 27.03.19 at 14:25, <jlpoole56@gmail.com> wrote:
>> On 3/27/2019 1:14 AM, Jan Beulich wrote:
>>>>>> On 26.03.19 at 18:21, <jlpoole56@gmail.com> wrote:
>>>> zeta /usr/local/src/xen # cat xen/.config |grep CONFIG_HVM
>>>> # CONFIG_HVM is not set
>>>> zeta /usr/local/src/xen #
>>>>
>>>> # tried 2 boot attempts
>>>> log at: https://pastebin.com/nL4BWJ6Y
>>>>
>>>> Hang points at lines:
>>> Thanks for trying anyway; one further possibility eliminated. Looking
>>> at the logs I've had another thought (wild guess again, so not really
>>> much hope): Could you try "mwait-idle=no"?
>>>
>> I modified man_xen.cfg by adding at the end the kernel parameter:
>>
>> mwait-idle=no
>>
>> Rebooted.
>> Result: hung:
> Thanks. I'm afraid I'm out of ideas for the moment.
>
> Jan
>
>
Jan,

Recall, the Xen kernel successfully launched in 2017 when I first built
Xen in Gentoo, that was about version 4.7.1.  I had to launch it
from an EFI console.  I've tried to revert back to 4.7.1 and
build a kernel and I have found it too difficult as certain
dependencies have since been removed from Gentoo.

I've been studying apic.c and the differences between 4.7.1
and HEAD.  Here's a DIFF:

http://quickdiff.net/?unique_id=948598C4-31A2-D028-CE95-F04632C1871A
Create a new one? <https://quickdiff.net/>

I see that currently there is a structure:

static const struct x86_cpu_id __initconstrel deadline_match[] = {

which identifies the microarchitecture, e.g. Haswell, Skylake.

https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/apic.c;h=2a2432619e3edce2cdbc275abbd4e80ffcdcd9f0;hb=HEAD#l1146


Line 1176 has a return if there is a failure to match, yet further down 
if there
is a version mismatch, there is a XENLOG_WARNING:

TSC_DEADLINE disabled due to Errata;
please update microcode to version %#x (or later)


My serveris Atom based, a Supermicro A1SAi-2750F
https://www.supermicro.com/products/motherboard/Atom/X10/A1SAi-2750F.cfm
which has an Intel® Atom™ Processor C2750.

https://ark.intel.com/content/www/us/en/ark/products/77987/intel-atom-processor-c2750-4m-cache-2-40-ghz.html

I believe my CPU chip is from a 22 nanometer fabrication process and
Wikipedia tells me that accordingly, the microarchitecture is Silvermont.
https://en.wikipedia.org/wiki/List_of_Intel_CPU_microarchitectures#Atom_Lines

Moreover, the Intel documentation confirms this:

"2.1.15 The Intel® Atom™ Processor Family Based on Silvermont 
Microarchitecture (2013)
Intel Atom Processor C2xxx, E3xxx, S1xxx series are based on the
Silvermont microarchitecture. Processors based on the Silvermont
microarchitecture supports instruction set extensions up to and
including SSE4.2, AESNI, and PCLMULQDQ."  from page 2-5 of the
Software Developer’s Manual (below).

I'm wondering if the fact that I was able to boot a kernel under Xen 2.4.7
and the unexplained hanging at boot for 4.7.12+ is related to the fact 
that the
Silvermont architecture is not accounted from in the deadline structure.

sheet 784-5 states that bit 24 "TSC-Deadline" with this description:
"A value of 1 indicates that the processor’s local APIC timer supports
one-shot operation using a TSC deadline value."

from the Intel® 64 and IA-32 Architectures
Software Developer’s Manual
Combined Volumes:
1, 2A, 2B, 2C, 2D, 3A, 3B, 3C, 3D and 4

at:
https://software.intel.com/sites/default/files/managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf

Is any of the above bird-dogging helpful or cause you to have an
"Ahah!" moment?

John




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