linux-kernel - [PATCH v4 0/2] arm64: Support FEAT_LSFE (Large System Float Extension)

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Message-Id: <20250918-arm64-lsfe-v4-0-0abc712101c7@kernel.org>
Date: Thu, 18 Sep 2025 20:42:05 +0100
From: Mark Brown <broonie@...nel.org>
To: 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, Mark Brown <broonie@...nel.org>
Subject: [PATCH v4 0/2] arm64: Support FEAT_LSFE (Large System Float
 Extension)

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>
---
Changes in v4:
- Rebase onto arm64/for-next/cpufeature, note that both patches have
  build dependencies on this.
- Drop unneeded cc clobber in hwcap.
- Use STRFADD as the instruction probed in hwcap.
- Link to v3: https://lore.kernel.org/r/20250818-arm64-lsfe-v3-0-af6f4d66eb39@kernel.org

Changes in v3:
- Rebase onto v6.17-rc1.
- Link to v2: https://lore.kernel.org/r/20250703-arm64-lsfe-v2-0-eced80999cb4@kernel.org

Changes in v2:
- Fix result of vi dropping in hwcap test.
- Link to v1: https://lore.kernel.org/r/20250627-arm64-lsfe-v1-0-68351c4bf741@kernel.org

---
Mark Brown (2):
      KVM: arm64: Expose FEAT_LSFE to guests
      kselftest/arm64: Add lsfe to the hwcaps test

 arch/arm64/kvm/sys_regs.c                 |  4 +++-
 tools/testing/selftests/arm64/abi/hwcap.c | 21 +++++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
---
base-commit: 220928e52cb03d223b3acad3888baf0687486d21
change-id: 20250625-arm64-lsfe-0810cf98adc2

Best regards,
--  
Mark Brown <broonie@...nel.org>