[PATCH v6 09/19] KVM: arm64: Write fast path PMU register handlers

[Colton Lewis]

Marc Zyngier <maz at kernel.org> writes:

> On Mon, 09 Feb 2026 22:14:04 +0000,
> Colton Lewis <coltonlewis at google.com> wrote:

>> We may want a partitioned PMU but not have FEAT_FGT to untrap the
>> specific registers that would normally be untrapped. Add a handler for
>> those registers in the fast path so we can still get a performance
>> boost from partitioning.

>> The idea is to handle traps for all the PMU registers quickly by
>> writing directly to the hardware when possible instead of hooking into
>> the emulated vPMU as the standard handlers in sys_regs.c do.

> This seems extremely premature. My assumption is that PMU traps are
> rare, and that doing a full exit should be acceptable. Until you
> demonstrate the contrary, I don't want this sort of massive bloat in
> the most performance-critical path.

After some consideration I agree. I will try a full exit and see if that
is sufficient.