linux-kernel - Re: [PATCH] x86/apic: Remove logical destination mode for 64-bit

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240729073651.GAZqdGk97FQzkGCPS8@fat_crate.local>
Date: Mon, 29 Jul 2024 09:36:51 +0200
From: Borislav Petkov <bp@...en8.de>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Rob <rob@...endal.co.uk>, Christian Heusel <christian@...sel.eu>,
	regressions@...ts.linux.dev, x86@...nel.org,
	Joerg Roedel <joro@...tes.org>, Tony Luck <tony.luck@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Menzel <pmenzel@...gen.mpg.de>, Lyude Paul <lyude@...hat.com>
Subject: Re: [PATCH] x86/apic: Remove logical destination mode for 64-bit

On Sun, Jul 28, 2024 at 01:06:10PM +0200, Thomas Gleixner wrote:
> Logical destination mode of the local APIC is used for systems with up to
> 8 CPUs. It has an advantage over physical destination mode as it allows to
> target multiple CPUs at once with IPIs.
> 
> That advantage was definitely worth it when systems with up to 8 CPUs
> were state of the art for servers and workstations, but that's history.
> 
> Aside of that there are systems which fail to work with logical destination
> mode as the ACPI/DMI quirks show and there are AMD Zen1 systems out there
> which fail when interrupt remapping is enabled. The latter can be cured by
> firmware updates, but not all OEMs distribute the required changes.
> 
> Physical destination mode is guaranteed to work because it is the only way
> to get a CPU up and running via the INIT/INIT/STARTUP sequence.
> 
> As the number of CPUs keeps increasing, logical destination mode becomes a
> less used code path so there is no real good reason to keep it around.
> 
> Therefore remove logical destination mode support for 64-bit and default to
> physical destination mode.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/include/asm/apic.h         |    8 --
>  arch/x86/kernel/apic/apic_flat_64.c |  119 ++----------------------------------
>  2 files changed, 7 insertions(+), 120 deletions(-)

Boots on my Zen1 but then again, it never had those Zen1 client problems to
begin with...

Anyway

Tested-by: Borislav Petkov (AMD) <bp@...en8.de>

Thx.

-- 
Regards/Gruss,
    Boris.

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