+ um-define-kernel_fpu_begin_mask.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: um: define kernel_fpu_begin_mask()
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     um-define-kernel_fpu_begin_mask.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/um-define-kernel_fpu_begin_mask.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Eric Biggers <ebiggers@kernel.org>
Subject: um: define kernel_fpu_begin_mask()
Date: Wed, 11 Nov 2026 12:56:02 -0800

Patch series "lib/raid: opt out of initializing MXCSR and 387 state".

This series slightly reduces the overhead of the x86 kernel-mode "FPU"
sections in the RAID code by using kernel_fpu_begin_mask(0) instead of
kernel_fpu_begin(), thus opting out of the 'ldmxcsr' (and on 32-bit
kernels, also 'fninit').  MXCSR is irrelevant for integer code.

This mirrors similar optimizations for the crypto and CRC code
(https://lore.kernel.org/linux-crypto/20261105005523.84925-1-ebiggers@kernel.org/).
It's more important there than in the RAID code, since short lengths are
common in the x86-optimized crypto and CRC functions.  However, I think
it's worth updating the RAID code too for consistency.

Unlike the crypto and CRC code, the RAID code is built for user-mode
Linux.  Therefore, as a prerequisite for this change, patch 1 also
defines a stub for kernel_fpu_begin_mask() on user-mode Linux.


This patch (of 3):

Define a stub for kernel_fpu_begin_mask() on user-mode Linux so that
lib/raid/ can switch from kernel_fpu_begin() to kernel_fpu_begin_mask().

Note: this causes a checkpatch error due to the macro's value not having
outer parentheses, but it's left as-is for consistency with the existing
kernel_fpu_begin() and kernel_fpu_end() definitions right next to it.

Link: https://lore.kernel.org/20261111205604.47547-1-ebiggers@kernel.org
Link: https://lore.kernel.org/20261111205604.47547-2-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
---

 arch/um/include/asm/fpu/api.h |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/um/include/asm/fpu/api.h~um-define-kernel_fpu_begin_mask
+++ a/arch/um/include/asm/fpu/api.h
@@ -11,6 +11,7 @@
  * UML code tree. */
 
 #define kernel_fpu_begin() (void)0
+#define kernel_fpu_begin_mask(mask) (void)(mask)
 #define kernel_fpu_end() (void)0
 
 static inline bool irq_fpu_usable(void)
_

Patches currently in -mm which might be from ebiggers@kernel.org are

xor-remove-obsolete-mmx-optimized-code.patch
raid6-remove-obsolete-mmx-optimized-code.patch
raid6-simplify-cpu-feature-checks.patch
um-define-kernel_fpu_begin_mask.patch
xor-opt-out-of-initializing-mxcsr-and-387-state.patch
raid6-opt-out-of-initializing-mxcsr-and-387-state.patch