Re: cleanup the RAID5 XOR library v4

Ard Biesheuvel
2026-03-27T10:38:03Z

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.