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

[Marc Zyngier]

On Mon, 09 Feb 2026 22:14:04 +0000,
Colton Lewis <coltonlewis@xxxxxxxxxx> 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.

"Start walking before you try to run".

	M.

-- 
Without deviation from the norm, progress is not possible.