Re: [PATCH] arm64: Expose AIDR_EL1 via sysfs

[Cornelia Huck <cohuck@redhat.com>]

On Thu, Apr 03 2025, Oliver Upton <oliver.upton@linux.dev> wrote:

> The KVM PV ABI recently added a feature that allows the VM to discover
> the set of physical CPU implementations, identified by a tuple of
> {MIDR_EL1, REVIDR_EL1, AIDR_EL1}. Unlike other KVM PV features, the
> expectation is that the VMM implements the hypercall instead of KVM as
> it has the authoritative view of where the VM gets scheduled.
>
> To do this the VMM needs to know the values of these registers on any
> CPU in the system. While MIDR_EL1 and REVIDR_EL1 are already exposed,
> AIDR_EL1 is not. Provide it in sysfs along with the other identification
> registers.
>
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> ---
>  Documentation/ABI/testing/sysfs-devices-system-cpu |  1 +
>  Documentation/arch/arm64/cpu-feature-registers.rst | 13 +++++++------
>  arch/arm64/include/asm/cpu.h                       |  1 +
>  arch/arm64/kernel/cpuinfo.c                        |  3 +++
>  4 files changed, 12 insertions(+), 6 deletions(-)

Indeed, AIDR_EL1 should be available alongside the others.

Reviewed-by: Cornelia Huck <cohuck@redhat.com>