Re: [PATCH] x86/lib: make clean_cache_range() zero-size safe

[Andrew Morton]

On Thu,  3 Sep 2026 15:11:25 +0800 "Li Zhe" <lizhe.67@xxxxxxxxxxxxx> wrote:

> clean_cache_range() writes back each cache line in the range
> [addr, addr + size). A zero-size range is empty and should not perform
> any cache maintenance operation.
> 
> As pointed out by Sashiko [1], clean_cache_range(addr, 0) currently can
> still execute one CLWB when addr is not cache-line aligned. With size 0,
> vend is equal to addr. However, the loop starts from the
> cacheline-aligned address containing addr. If addr is not cacheline
> aligned, that rounded-down start is below vend, so the loop can execute
> one CLWB even though the requested range is empty.
> 
> That gives zero-size callers observable side effects. For example,
> arch_wb_cache_pmem(addr, 0) should not write back any cache line, and
> memcpy_flushcache(dst, src, 0) should preserve the usual zero-length
> copy semantics. If the rounded-down line is not mapped, the stray CLWB
> can also fault.
> 
> Return immediately from clean_cache_range() for size 0.

Thanks.  Sashiko might have found a few similar issues in there:
	https://sashiko.dev/#/patchset/20260903071125.1946-1-lizhe.67@xxxxxxxxxxxxx