mm: rust: add vm_area_struct methods that require read access

This adds a type called VmaRef which is used when referencing a vma that
you have read access to.  Here, read access means that you hold either the
mmap read lock or the vma read lock (or stronger).

Additionally, a vma_lookup method is added to the mmap read guard, which
enables you to obtain a &VmaRef in safe Rust code.

This patch only provides a way to lock the mmap read lock, but a follow-up
patch also provides a way to just lock the vma read lock.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Alice Ryhl <[email protected]>
Acked-by: Lorenzo Stoakes <[email protected]>
Acked-by: Liam R. Howlett <[email protected]>
Reviewed-by: Jann Horn <[email protected]>
Reviewed-by: Andreas Hindborg <[email protected]>
Reviewed-by: Gary Guo <[email protected]>
Cc: Alex Gaynor <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Benno Lossin <[email protected]>
Cc: Björn Roy Baron <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Trevor Gross <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/rust/helpers/mm.c b/rust/helpers/mm.c
index 7201747a5d31..7b72eb065a3e 100644
--- a/rust/helpers/mm.c
+++ b/rust/helpers/mm.c
@@ -37,3 +37,9 @@ void rust_helper_mmap_read_unlock(struct mm_struct *mm)
 {
 	mmap_read_unlock(mm);
 }
+
+struct vm_area_struct *rust_helper_vma_lookup(struct mm_struct *mm,
+					      unsigned long addr)
+{
+	return vma_lookup(mm, addr);
+}