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

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Date:   Thu, 27 May 2021 13:49:42 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...e.de>, James Feeney <james@...ealm.net>
Cc:     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 12:31, Borislav Petkov wrote:
> @@ -1226,6 +1227,14 @@ void __init setup_arch(char **cmdline_p)
>  
>  	x86_init.timers.wallclock_init();
>  
> +	/*
> +	 * This needs to run before setup_local_APIC() which soft-disables the
> +	 * local APIC temporarily and that masks the thermal LVT interrupt,
> +	 * leading to softlockups on machines which have configured SMI
> +	 * interrupt delivery.
> +	 */
> +	therm_lvt_init();

That works, but TBH, it's a hack....

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

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.

Thanks,

        tglx