linux-kernel - Re: [patch 3/4] x86/topology: Handle the !APIC case gracefully

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Date: Fri, 22 Mar 2024 14:41:30 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 3/4] x86/topology: Handle the !APIC case gracefully

On Fri, Mar 22, 2024 at 07:56:38PM +0100, Thomas Gleixner wrote:
> If there is no local APIC enumerated and registered then the topology
> bitmaps are empty. Therefore topology_init_possible_cpus() will die with a
> division by zero exception.
> 
> Prevent this by registering a fake APIC id to populate the topology
> bitmap. This also allows to use all topology query interfaces
> unconditionally. It does not affect the actual APIC code because either the
> local APIC address was not registered or no local APIC could be detected.
> 
> Fixes: f1f758a80516 ("x86/topology: Add a mechanism to track topology via APIC IDs")
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter