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

[Catalin Marinas <catalin.marinas@arm.com>]

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).

One reason is that it's cheaper to compute the tlbi domains at context
switch time (bitmap-and IIRC) than working from mm_cpumask() every time
we do a TLBI.

That said, suggestions for a quick algorithm are welcome. Subject to the
race conditions Will mentioned, we could use the mm_cpumask() for a
quick check if we ever ran on that CPU and avoid recomputing the tlbi
domains.

-- 
Catalin