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

[Linu Cherian]

Hi Kristina,

On Thu, Oct 01, 2026 at 12:06:43PM +0100, Kristina Martšenko wrote:
> Hi,
> 
> 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

Lets say if we have a TLB domain of 8 cpus and a process has ran on only
one cpu, dont we end up broadcasting to all cpus in the domain as the 
granularity is at the domain level ?
If thats true, would be good to make that clear.


> patch explains a bit about how it works. This is an RFC since I'm not familiar
> with the kernel's TLB/mm code and I'd like feedback on whether the general
> approach is correct.
> 
> A few notes and open questions:
> 
>   * Domains are described in a new "TLBI" ACPI table. This is not yet part of
>     the ACPI specification. There was an initial proposal [2] but this series
>     uses a newer WIP version of the table that aims to be published by the end
>     of the year.
> 
>   * There is currently no device tree binding since the feature is mainly meant
>     for server-class systems.
> 
>   * It's also possible to use TLBI domains to limit a KVM guest's TLB
>     invalidations to CPUs where the guest has run. I'll try to include that in
>     the next version. This series only disables domains for guests.
> 
>   * With this series a long-running process may eventually run on all CPUs and
>     just issue broadcast TLBIs. It may be worth periodically reducing the set
>     of CPUs but it's not clear when.

Do you have some thoughts on how we could reduce the set of cpus, to avoid
cross domain scheduling ? 
IIUC, this should me more of a scheduling decision with domain awareness. 


Thanks,
Linu Cherian.