Re: [PATCH v1 2/9] x86/apic: Add helper to get maximum number of Extended LVT registers

[Naveen N Rao <naveen@kernel.org>]

On Wed, Feb 04, 2026 at 07:44:45AM +0000, Manali Shukla wrote:
> Add lapic_get_max_extlvt() to retrieve the maximum number of Extended
> LVT registers supported by the local APIC on AMD processors.  The count
> is read from APIC_EFEAT[23:16] (offset 0x400), per AMD APM Volume 2.
> 
> Extended LVT registers provide additional interrupt vectors beyond
> standard LVT entries, enabling features like Instruction Based Sampling
> (IBS). Current AMD processors support four extended LVT entries, but
> future processors may support up to 255.
> 
> Wrap lapic_get_max_extlvt() with kvm_cpu_get_max_extlvt() for use by
> KVM code. Subsequent patches will use this helper to configure the guest's
> extended APIC register space.
> 
> Signed-off-by: Manali Shukla <manali.shukla@amd.com>
> ---
>  arch/x86/include/asm/apic.h     |  1 +
>  arch/x86/include/asm/kvm_host.h | 10 ++++++++++
>  arch/x86/kernel/apic/apic.c     | 17 +++++++++++++++++
>  3 files changed, 28 insertions(+)

This shouldn't be required if we go with:
http://lore.kernel.org/r/78a4c3ddce65e2a79f23aea6fdc05faf4346d290.1778594390.git.naveen@kernel.org

- Naveen