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

["Zi Yan" <ziy@nvidia.com>]

On Thu Oct 1, 2026 at 7:06 AM EDT, 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

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).

Thanks.

> 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.
>
>   * There are currently no performance numbers since there is no hardware with
>     this feature yet.
>
>   * The series has been tested on an Arm FVP which supports the TLBID
>     architecture but does not have any domains (except domain 0).
>
> Any feedback is welcome.
>
> Thanks,
> Kristina
>
> [1] https://support.arm.com/architectures/a-profile-architecture#Downloads
> [2] https://github.com/tianocore/edk2/issues/11999
>
>
> Kristina Martšenko (12):
>   arm64: sysreg: Add definitions for FEAT_TLBID
>   arm64: Detect FEAT_TLBID
>   KVM: arm64: Hide TLBID from guest sysregs
>   KVM: arm64: Hide TLBID from guest instructions
>   ACPICA: Add TLBI table definition
>   ACPI: TLBI: Parse domains from table
>   arm64: tlbid: Set up CPU domain bitmaps
>   efi/arm: Check return value of init_new_context()
>   arm64: tlbid: Track the TLBI domain of a task
>   arm64: Support TLBIP instructions
>   arm64: tlbid: Pass domain to TLBI instructions
>   arm64: tlbid: Add documentation
>
>  Documentation/arch/arm64/booting.rst    |  10 ++
>  arch/arm64/Kconfig                      |  12 ++
>  arch/arm64/include/asm/acpi.h           |  10 ++
>  arch/arm64/include/asm/cpu.h            |   1 +
>  arch/arm64/include/asm/cpufeature.h     |  15 ++
>  arch/arm64/include/asm/el2_setup.h      |  76 +++++++-
>  arch/arm64/include/asm/kvm_emulate.h    |   5 +
>  arch/arm64/include/asm/mmu.h            |  13 ++
>  arch/arm64/include/asm/mmu_context.h    |   9 +-
>  arch/arm64/include/asm/tlbflush.h       | 219 +++++++++++++++++-------
>  arch/arm64/kernel/cpufeature.c          |  25 +++
>  arch/arm64/kernel/cpuinfo.c             |   3 +
>  arch/arm64/kvm/config.c                 |   6 +
>  arch/arm64/kvm/emulate-nested.c         |   1 +
>  arch/arm64/kvm/hyp/include/hyp/switch.h |   7 +-
>  arch/arm64/kvm/hyp/nvhe/tlb.c           |   2 +-
>  arch/arm64/kvm/hyp/vhe/tlb.c            |   4 +-
>  arch/arm64/kvm/sys_regs.c               |   3 +
>  arch/arm64/mm/Makefile                  |   1 +
>  arch/arm64/mm/context.c                 |   6 +-
>  arch/arm64/mm/tlbid.c                   | 210 +++++++++++++++++++++++
>  arch/arm64/tools/cpucaps                |   1 +
>  arch/arm64/tools/sysreg                 |  53 +++++-
>  drivers/acpi/arm64/Kconfig              |   3 +
>  drivers/acpi/arm64/Makefile             |   1 +
>  drivers/acpi/arm64/init.c               |   2 +
>  drivers/acpi/arm64/init.h               |   1 +
>  drivers/acpi/arm64/tlbi.c               | 196 +++++++++++++++++++++
>  drivers/firmware/efi/arm-runtime.c      |   3 +-
>  include/acpi/actbl2.h                   |  32 ++++
>  30 files changed, 858 insertions(+), 72 deletions(-)
>  create mode 100644 arch/arm64/mm/tlbid.c
>  create mode 100644 drivers/acpi/arm64/tlbi.c
>
>
> base-commit: 93f51579e7df248780214094418f205253383cc5




-- 
Best Regards,
Yan, Zi