Re: [RFC 00/12] arm64: Add support for TLBI domains

[Will Deacon <will@kernel.org>]

On Sun, Oct 04, 2026 at 02:06:48PM -0400, Zi Yan wrote:
> On Thu Oct 1, 2026 at 7:06 AM EDT, Kristina Martšenko wrote:
> > This series allows the kernel to use TLBI domains. TLBI domains (FEAT_TLBID) is
> > an Arm architecture feature that enables a TLB invalidation to target a subset
> > of CPUs instead of the whole system. It can improve performance on systems with
> > many CPUs. TLBID is not yet part of the Arm Architecture Reference Manual but
> > some of it is described in the latest XML [1].
> >
> > The goal of this series is to send TLBI commands only to the CPUs where a
> > process has run (i.e. where its page tables have been installed). The last
> 
> IIUC, mm_cpumask() is used to store this information on x86 and other
> archs. I see you put this information in tlbid_domains of mm_context_t
> from patch 9, although in the form of tlb id domains. I wonder why not
> make arm64 also update mm_cpumask() like x86 and other archs and derive
> the tlbid domains based on mm_cpumask() and a cpu-to-domain mapping
> (added in patch 7).

Historically, maintaining mm_cpumask() was a horrible source of contention
when we looked at it in the past. Maybe that's no longer true, but it
would be good to see some numbers if we want to start keeping that thing
accurate on arm64.

Will