linux-kernel - Re: X86 parallel bring up regression

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Message-ID: <450e06f8-5655-406e-b485-c19862bba6d8@amd.com>
Date:   Mon, 23 Oct 2023 11:04:31 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     x86@...nel.org, David Woodhouse <dwmw@...zon.co.uk>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Gong, Richard" <Richard.Gong@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux kernel regressions list <regressions@...ts.linux.dev>,
        Michael Kelley <mikelley@...rosoft.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Helge Deller <deller@....de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Subject: Re: X86 parallel bring up regression

On 10/19/2023 15:26, Mario Limonciello wrote:
> Hi,
> 
> We've recently found that there was a regression from 6.5 that broke 
> resume from suspend-to-ram on some AMD platforms.
> 
> We bisected it and confirmed it's introduced by 0c7ffa32dbd6 
> ("x86/smpboot/64: Implement arch_cpuhp_init_parallel_bringup() and 
> enable it").
> 
> Furthermore; we confirmed that on 6.6-rc6 adding cpuhp.parallel=0 to the 
> kernel command line avoids the issue.
> 
> Here are bootup kernel logs from an affected system at 7e75178 (doesn't 
> reproduce) and 0c7ffa32 (does reproduce).
> https://gist.github.com/superm1/c251c0849956b8389309f03871fba091
> 
> Is it possible that this is caused by the system entering S3 with x2apic 
> enabled but leaving with it disabled?
> 
> I notice in the resume path on a boot with cpuhp.parallel=0 that x2apic 
> "explicitly" gets turned on again.
> 
> <snip>
> smpboot: CPU 127 is now offline
> ACPI: PM: Low-level resume complete
> ACPI: PM: Restoring platform NVS memory
> x2apic enabled
> AMD-Vi: Virtual APIC enabled
> AMD-Vi: Virtual APIC enabled
> LVT offset 0 assigned for vector 0x400
> Enabling non-boot CPUs ...
> smpboot: Booting Node 0 Processor 1 APIC 0x2
> masked ExtINT on CPU#1
> ACPI: \_SB_.PLTF.C002: Found 2 idle states
> CPU1 is up
> smpboot: Booting Node 0 Processor 2 APIC 0x4
> </snip>
> 
> I hypothesize this could be caused by .Lread_apicid finding x2apic 
> disabled but then trying to read from apic_mmio_base which isn't 
> initialized because x2apic was used (AFAICT apic_set_fixmap() never gets 
> called in this case).
> 
> Thanks,

AFAICT the issue is indeed that x2apic isn't re-enabled during s3
resume.

I've posted a series that I confirmed resolves the issue here:

https://lore.kernel.org/all/20231023160018.164054-1-mario.limonciello@amd.com/T/#t