linux-kernel - Re: [PATCH] x86/apic: Handle missing global clockevent gracefully

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Message-ID: <3ca04aaf-c67a-d449-dac9-0fe5bc431009@suse.cz>
Date:   Mon, 12 Aug 2019 09:03:36 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Daniel Drake <drake@...lessm.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Endless Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: [PATCH] x86/apic: Handle missing global clockevent gracefully

On 12. 08. 19, 8:16, Daniel Drake wrote:
> On Fri, Aug 9, 2019 at 8:54 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>> Some newer machines do not advertise legacy timers. The kernel can handle
>> that situation if the TSC and the CPU frequency are enumerated by CPUID or
>> MSRs and the CPU supports TSC deadline timer. If the CPU does not support
>> TSC deadline timer the local APIC timer frequency has to be known as well.
>>
>> Some Ryzens machines do not advertize legacy timers, but there is no
>> reliable way to determine the bus frequency which feeds the local APIC
>> timer when the machine allows overclocking of that frequency.
>>
>> As there is no legacy timer the local APIC timer calibration crashes due to
>> a NULL pointer dereference when accessing the not installed global clock
>> event device.
>>
>> Switch the calibration loop to a non interrupt based one, which polls
>> either TSC (frequency known) or jiffies. The latter requires a global
>> clockevent. As the machines which do not have a global clockevent installed
>> have a known TSC frequency this is a non issue. For older machines where
>> TSC frequency is not known, there is no known case where the legacy timers
>> do not exist as that would have been reported long ago.
> 
> This solves the problem I described in the thread:
>     setup_boot_APIC_clock() NULL dereference during early boot on
> reduced hardware platforms

So it does for the openSUSE user:
http://bugzilla.opensuse.org/show_bug.cgi?id=1142926#c12

=========
After installing that build of the kernel from your OBS home project,
that did
more than just fix the issue with the APIC timer screwing up. I now have
all 4
cores/8 threads available.

I do see some errors from the ACPI layer that do indicate that there are
some
areas of the BIOS from HP that are buggy, but at this time, the machine
seems
to be working without issue.
=========

dmesg here:
http://bugzilla.opensuse.org/attachment.cgi?id=813577

thanks,
-- 
js
suse labs