linux-kernel - Re: [PATCH v2] x86/CPU/AMD: Prevent reset reasons from being retained among boots

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Message-ID: <20251013153440.GA78919@yaz-khff2.amd.com>
Date: Mon, 13 Oct 2025 11:34:40 -0400
From: Yazen Ghannam <yazen.ghannam@....com>
To: Rong Zhang <i@...g.moe>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Mario Limonciello <mario.limonciello@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/CPU/AMD: Prevent reset reasons from being
 retained among boots

On Sat, Oct 11, 2025 at 12:59:58AM +0800, Rong Zhang wrote:
> The S5_RESET_STATUS register is parsed on boot and printed to kmsg.
> However, this could sometimes be misleading and lead to users wasting a
> lot of time on meaningless debugging for two reasons:
> 
> * Some bits are never cleared by hardware. It's the software's
> responsibility to clear them as per the Processor Programming Reference
> (see Link:).
> 
> * Some rare hardware-initiated platform resets do not update the
> register at all.
> 
> In both cases, a previous reboot could leave its trace in the register,
> resulting in users seeing unrelated reboot reasons while debugging
> random reboots afterward.
> 
> Clearing all reason bits solves the issue. Since all reason bits are
> write-1-to-clear and we must preserve all other bits, this is done by
> writing the read value back to the register.
> 
> Fixes: ab8131028710 ("x86/CPU/AMD: Print the reason for the last reset")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537#attach_303991
> Signed-off-by: Rong Zhang <i@...g.moe>
> ---

Reviewed-by: Yazen Ghannam <yazen.ghannam@....com>

Thanks,
Yazen