linux-kernel - Re: [PATCH] x86/thermal: Fix LVT thermal setup for SMI delivery mode

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Message-ID: <YK+JC9qjkEuz/aaz@zn.tnic>
Date:   Thu, 27 May 2021 13:56:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     James Feeney <james@...ealm.net>, linux-smp@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        lkml <linux-kernel@...r.kernel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        x86-ml <x86@...nel.org>
Subject: Re: [PATCH] x86/thermal: Fix LVT thermal setup for SMI delivery mode

On Thu, May 27, 2021 at 01:49:42PM +0200, Thomas Gleixner wrote:
> That works, but TBH, it's a hack....

Yeah, it restores to the previous behavior.

> What I really fail to understand is how disabling that LVT entry makes
> the machine lock up.

The observation is is that on James' box, *sometimes* - not always - it
would softlockup on CPU0 without this early LVT thermal read.

I can try to reproduce on the box I have here, lemme see...

> Also if disabling this entry is causing the BIOS/SMM gunk to go south, then
> disabling CONFIG_X86_THERMAL_VECTOR should have the same effect.
> 
> Which made me look at other places like lapic_suspend/resume which does
> the save/restore Kconfig conditional as well.

The fact that it doesn't reproduce always shows that there's something
else at play too. As I said in the commit message: "Those soft lockups
are not 100% reproducible and the reason for that can only be speculated
as no one tells you what SMM does."

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette