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

[Borislav Petkov]

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@xxxxxxxxxxxxx>
> ---
>  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@xxxxxxxxx>

Thx.

-- 
Regards/Gruss,
    Boris.

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