Re: [PATCH] rust: helpers: add is_vmalloc_addr wrapper for NOMMU builds

[Miguel Ojeda]

On Fri, May 22, 2026 at 8:54 PM Shivam Kalra via B4 Relay
<devnull+shivamkalra98.zohomail.in@xxxxxxxxxx> wrote:
>
> From: Shivam Kalra <shivamkalra98@xxxxxxxxxxx>
>
> Commit 47ac2a4b5cd8 ("rust: kvec: implement shrink_to for KVVec")
> introduced a call to bindings::is_vmalloc_addr(). However, this
> fails to compile on architectures where CONFIG_MMU is disabled,
> resulting in the following build error:
>
>     error[E0425]: cannot find function is_vmalloc_addr in crate bindings
>
> When CONFIG_MMU is not set, is_vmalloc_addr() is defined as a
> static inline function in <linux/mm.h> that unconditionally
> returns false. Because bindgen skips static inline functions
> when generating bindings, the symbol is completely missing from
> the Rust bindings crate.
>
> Fix this by providing a C helper wrapper, rust_helper_is_vmalloc_addr(),
> in rust/helpers/vmalloc.c. This ensures the function is reliably
> exposed to Rust regardless of the MMU configuration. On NOMMU builds,
> this allows KVVec::shrink_to() to successfully compile and correctly
> route all allocations through the kmalloc realloc path.
>
> Fixes: 47ac2a4b5cd8 ("rust: kvec: implement shrink_to for KVVec")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605220811.LRplxeBR-lkp@xxxxxxxxx/
> Signed-off-by: Shivam Kalra <shivamkalra98@xxxxxxxxxxx>

I can take this in my `rust-fixes` PR unless mm/akpm plans to do so.

Cc'ing akpm, Lorenzo, Liam and linux-mm, by the way.

Thanks!

Cheers,
Miguel