Re: cleanup the RAID5 XOR library v4

["Ard Biesheuvel" <ardb@kernel.org>]

On Fri, 27 Mar 2026, at 07:16, Christoph Hellwig wrote:
> Hi all,
>
> the XOR library used for the RAID5 parity is a bit of a mess right now.
> The main file sits in crypto/ despite not being cryptography and not
> using the crypto API, with the generic implementations sitting in
> include/asm-generic and the arch implementations sitting in an asm/
> header in theory.  The latter doesn't work for many cases, so
> architectures often build the code directly into the core kernel, or
> create another module for the architecture code.
>
> Changes this to a single module in lib/ that also contains the
> architecture optimizations, similar to the library work Eric Biggers
> has done for the CRC and crypto libraries later.  After that it changes
> to better calling conventions that allow for smarter architecture
> implementations (although none is contained here yet), and uses
> static_call to avoid indirection function call overhead.
>
> A git tree is also available here:
>
>     git://git.infradead.org/users/hch/misc.git xor-improvements
>
> Gitweb:
>
>     
> https://git.infradead.org/?p=users/hch/misc.git;a=shortlog;h=refs/heads/xor-improvements
>
> Changes since v3:
>  - switch away from lockdep_assert_preemption_enabled() again
>  - fix a @ reference in a kerneldoc comment.
>  - build the arm4regs implementation also without kernel-mode neon
>    support
>  - fix a pre-existing issue about mismatched attributes on arm64's
>    xor_block_inner_neon
>  - reject 0-sized xor request and adjust the kunit test case to not
>    generate them
>
> Changes since v2:
>  - drop use of CONFIG_KERNEL_MODE_NEON for arm64
>  - drop the new __limit_random_u32_below for the unit test
>  - require 64-bit alignment because sparc64 requires it
>  - use DEFINE_STATIC_CALL_NULL to avoid exposing a specific xor_gen
>    routine
>  - keep CONFIG_XOR_BLOCKS_ARCH self-contained in lib/raid/
>  - don't select library option from kunit test and add a .kunitconfig
>    instead
>  - fix the module description for the kunit test
>  - add a case where buffers are at the end of the allocation in the kunit test
>  - use separate src/dst alignment in the kunit test
>  - fix and improve the kunit assert message
>
> Changes since v1:
>  - use lockdep_assert_preemption_enabled()
>  - improve the commit message for the initial um xor.h cleanup
>  - further clean up the um arch specific header
>  - add SPDX identifier to the new build system files
>  - use bool for xor_forced
>  - fix an incorrect printk level conversion from warn to info
>  - include xor_impl.h in xor-neon.c
>  - remove unused exports for riscv
>  - simply move the sparc code instead of splititng it
>  - simplify the makefile for the x86-specific implementations
>  - remove stray references to xor_blocks in crypto/async_tx
>  - rework __DO_XOR_BLOCKS to avoid (theoretical) out of bounds references
>  - improve the kerneldoc API documentration for xor_gen()
>  - spell the name of the srcs argument to xor_gen correctly in xor.h
>  - add a kunit test, and a new random helper for it.
>

For the series,

Acked-by: Ard Biesheuvel <ardb@kernel.org>

As discussed, arm64 and ARM can share the NEON intrinsics implementation, which would allow for a bit of cleanup as well. I'll follow up with some patches based on this series.