mm: rust: add lock_vma_under_rcu

Currently, the binder driver always uses the mmap lock to make changes to
its vma.  Because the mmap lock is global to the process, this can involve
significant contention.  However, the kernel has a feature called per-vma
locks, which can significantly reduce contention.  For example, you can
take a vma lock in parallel with an mmap write lock.  This is important
because contention on the mmap lock has been a long-term recurring
challenge for the Binder driver.

This patch introduces support for using `lock_vma_under_rcu` from Rust. 
The Rust Binder driver will be able to use this to reduce contention on
the mmap lock.

Link: https://lkml.kernel.org/r/20250408-vma-v16-4-d8b446e885d9@google.com
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Cc: Alex Gaynor <alex.gaynor@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <balbirs@nvidia.com>
Cc: Benno Lossin <benno.lossin@proton.me>
Cc: Björn Roy Baron <bjorn3_gh@protonmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Trevor Gross <tmgross@umich.edu>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/rust/helpers/mm.c b/rust/helpers/mm.c
index 7b72eb065a3e..81b510c96fd2 100644
--- a/rust/helpers/mm.c
+++ b/rust/helpers/mm.c
@@ -43,3 +43,8 @@ struct vm_area_struct *rust_helper_vma_lookup(struct mm_struct *mm,
 {
 	return vma_lookup(mm, addr);
 }
+
+void rust_helper_vma_end_read(struct vm_area_struct *vma)
+{
+	vma_end_read(vma);
+}