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

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

[Shivam Kalra via B4 Relay]

From: Shivam Kalra <shivamkalra98@zohomail.in>

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@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202605220811.LRplxeBR-lkp@intel.com/
Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>
---
 rust/helpers/vmalloc.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/rust/helpers/vmalloc.c b/rust/helpers/vmalloc.c
index 326b030487a2..6aed13292313 100644
--- a/rust/helpers/vmalloc.c
+++ b/rust/helpers/vmalloc.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/mm.h>
 #include <linux/vmalloc.h>
 
 __rust_helper void *__must_check __realloc_size(2)
@@ -8,3 +9,8 @@ rust_helper_vrealloc_node_align(const void *p, size_t size, unsigned long align,
 {
 	return vrealloc_node_align(p, size, align, flags, node);
 }
+
+__rust_helper bool rust_helper_is_vmalloc_addr(const void *x)
+{
+	return is_vmalloc_addr(x);
+}

---
base-commit: 6779b50faa562e6cca1aa6a4649a4d764c6c7e28
change-id: 20260522-is-vmalloc-addr-build-fix-abc614b17877

Best regards,
--  
Shivam Kalra <shivamkalra98@zohomail.in>

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

[Alice Ryhl]

On Fri, May 22, 2026 at 8:54 PM Shivam Kalra via B4 Relay
<devnull+shivamkalra98.zohomail.in@kernel.org> wrote:
>
> From: Shivam Kalra <shivamkalra98@zohomail.in>
>
> 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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605220811.LRplxeBR-lkp@intel.com/
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

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@kernel.org> wrote:
>
> From: Shivam Kalra <shivamkalra98@zohomail.in>
>
> 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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605220811.LRplxeBR-lkp@intel.com/
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>

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

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

[Danilo Krummrich]

On 5/22/26 8:54 PM, Shivam Kalra via B4 Relay wrote:
> From: Shivam Kalra <shivamkalra98@zohomail.in>
> 
> 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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605220811.LRplxeBR-lkp@intel.com/
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>

Reviewed-by: Danilo Krummrich <dakr@kernel.org>

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@kernel.org> wrote:
>
> From: Shivam Kalra <shivamkalra98@zohomail.in>
>
> 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@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202605220811.LRplxeBR-lkp@intel.com/
> Signed-off-by: Shivam Kalra <shivamkalra98@zohomail.in>

Applied to `rust-fixes` -- thanks everyone!

    [ Pasted exact compiler output and expanded it. - Miguel ]

The compiler output did not seem to be an exact copy paste for some
reason (at least from my testing when reproducing the issue), so I
updated the compiler output.

Cheers,
Miguel