Subject: Re: [PATCH 0/2] arm64: add finalized cap helper

From: Marc Zyngier <[email-masked]>
Date: Mon, 17 Feb 2020 14:48:04 +0000

On 2020-02-10 12:27, Mark Rutland wrote:
> Across arm64 we use cpus_have_const_cap() to check for a capability
> without a runtime check. Prior to capabilities being finalized
> cpus_have_const_cap() falls back to a runtime check of the cpu_hwcaps
> array. In some cases we know that code is never invoked prior to the
> capabilities being finalized, and the fallback code is redundant (and
> unsound if ever executed in hyp context).
> 
> So that we can avoid the redundant code and detect when the caps are
> unexpectedly checked too early, this series adds a new
> cpus_have_final_cap() helper, and migrates the KVM hyp code over to it.
> 
> I'm hoping to use this as part of the entry.S -> entry-common.c
> conversion, and there are other places in arm64 that could potentially
> use this today.
> 
> Thanks,
> Mark.
> 
> Mark Rutland (2):
>   arm64: cpufeature: add cpus_have_final_cap()
>   arm64: kvm: hyp: use cpus_have_final_cap()
> 
>  arch/arm64/include/asm/cpufeature.h | 47 
> +++++++++++++++++++++++++++++++++----
>  arch/arm64/kvm/hyp/switch.c         | 14 +++++------
>  arch/arm64/kvm/hyp/sysreg-sr.c      |  8 +++----
>  arch/arm64/kvm/hyp/tlb.c            |  8 +++----
>  4 files changed, 57 insertions(+), 20 deletions(-)

Seems like a valuable optimization. For the series:

Reviewed-by: Marc Zyngier <[email-masked]>

         M.
-- 
Jazz is not dead. It just smells funny...

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