Re: [PATCH 0/2] arm64: tlb: Optimize ARM64_WORKAROUND_REPEAT_TLBI

[Marc Zyngier <maz@kernel.org>]

On Wed, 18 Feb 2026 16:43:46 +0000,
Mark Rutland <mark.rutland@arm.com> wrote:
> 
> Hi all,
> 
> Some Arm partners have complained that the overhead of
> ARM64_WORKAROUND_REPEAT_TLBI is too large, and despite the relevant
> errata being categorized as "rare", they still want to use the
> workaround in some deployments.
> 
> For historical reasons, the current workaround is far stronger (and
> consequently far more expensive) than necessary. In part, the SDENs had
> somewhat misleading descriptions, which have recently been clarified:
> 
> * Arm Cortex-A76 erratum #1286807
>   SDEN v33: https://developer.arm.com/documentation/SDEN-885749/33-0/
> 
> * Arm Cortex-A55 erratum #2441007
>   SDEN v16: https://developer.arm.com/documentation/SDEN-859338/1600/
> 
> * Arm Cortex-A510 erratum #2441009
>   SDEN v19: https://developer.arm.com/documentation/SDEN-1873351/1900/
> 
> Patch 1 allows the __TLBI*() helpers to generate XZR as an argument.
> I've split this out as its own patch to make bisection easier in case we
> see any problems due to incorrect trap+emulation handling of XZR.
> Otherwise this shouldn't have any functional change.
> 
> Patch 2 is the actual optimization, spelled out in detail in the commit
> message. The gist is that it's not necessary to duplicate every
> individual TLBI, and it's sufficient to have a single arbitrary TLBI;DSB
> after any number of batched TLBIs;DSB.
> 
> As mentioned in the commit message for patch 2, this results in fewer
> alternatives and better code generation whenever
> ARM64_WORKAROUND_REPEAT_TLBI is built into the kernel, so it's a
> (trivial) win on hardware that isn't affected by the relevant errata.
> 
> Mark.
> 
> Mark Rutland (2):
>   arm64: tlb: Allow XZR argument to TLBI ops
>   arm64: tlb: Optimize ARM64_WORKAROUND_REPEAT_TLBI
> 
>  arch/arm64/include/asm/tlbflush.h | 63 ++++++++++++++++++-------------
>  arch/arm64/kernel/sys_compat.c    |  2 +-
>  arch/arm64/kvm/hyp/nvhe/mm.c      |  2 +-
>  arch/arm64/kvm/hyp/nvhe/tlb.c     |  8 ++--
>  arch/arm64/kvm/hyp/pgtable.c      |  2 +-
>  arch/arm64/kvm/hyp/vhe/tlb.c      | 10 ++---
>  6 files changed, 49 insertions(+), 38 deletions(-)
> 

A bit late, but FTR,

Reviewed-by: Marc Zyngier <maz@kernel.org>

	M.

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