linux-kernel - Re: [PATCH 0/3] arm64: Support FEAT_LSFE (Large System Float Extension)

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Message-ID: <ee89d23e-db04-4646-a556-27117e94b5ed@arm.com>
Date: Mon, 30 Jun 2025 11:21:14 +0100
From: Ben Horgan <ben.horgan@....com>
To: Mark Brown <broonie@...nel.org>, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>, Joey Gouly <joey.gouly@....com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Shuah Khan <shuah@...nel.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 0/3] arm64: Support FEAT_LSFE (Large System Float
 Extension)

Hi Mark,

On 6/27/25 18:20, Mark Brown wrote:
> FEAT_LSFE is optional from v9.5, it adds new instructions for atomic
> memory operations with floating point values.  We have no immediate use
> for it in kernel, provide a hwcap so userspace can discover it and allow
> the ID register field to be exposed to KVM guests.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
> Mark Brown (3):
>        arm64/hwcap: Add hwcap for FEAT_LSFE
>        KVM: arm64: Expose FEAT_LSFE to guests
>        kselftest/arm64: Add lsfe to the hwcaps test
> 
>   Documentation/arch/arm64/elf_hwcaps.rst   |  4 ++++
>   arch/arm64/include/asm/hwcap.h            |  1 +
>   arch/arm64/include/uapi/asm/hwcap.h       |  1 +
>   arch/arm64/kernel/cpufeature.c            |  2 ++
>   arch/arm64/kernel/cpuinfo.c               |  1 +
>   arch/arm64/kvm/sys_regs.c                 |  4 +++-
>   tools/testing/selftests/arm64/abi/hwcap.c | 21 +++++++++++++++++++++
>   7 files changed, 33 insertions(+), 1 deletion(-)


I have looked through the series and it looks good to me modulo a couple 
of minor comments left on the patches. Bare in mind fairly new here and 
this is the first use of hwcap3 so I expect more experienced review is 
required.

Reviewed-by: Ben Horgan <ben.horgan@....com>

> ---
> base-commit: 86731a2a651e58953fc949573895f2fa6d456841
> change-id: 20250625-arm64-lsfe-0810cf98adc2
> 
> Best regards,
> --
> Mark Brown <broonie@...nel.org>
> 
> 


Thanks,

Ben