mm/mmap: reorganize munmap to use maple states

Remove __do_munmap() in favour of do_munmap(), do_mas_munmap(), and
do_mas_align_munmap().

do_munmap() is a wrapper to create a maple state for any callers that have
not been converted to the maple tree.

do_mas_munmap() takes a maple state to mumap a range.  This is just a
small function which checks for error conditions and aligns the end of the
range.

do_mas_align_munmap() uses the aligned range to mumap a range.
do_mas_align_munmap() starts with the first VMA in the range, then finds
the last VMA in the range.  Both start and end are split if necessary.
Then the VMAs are removed from the linked list and the mm mlock count is
updated at the same time.  Followed by a single tree operation of
overwriting the area in with a NULL.  Finally, the detached list is
unmapped and freed.

By reorganizing the munmap calls as outlined, it is now possible to avoid
extra work of aligning pre-aligned callers which are known to be safe,
avoid extra VMA lookups or tree walks for modifications.

detach_vmas_to_be_unmapped() is no longer used, so drop this code.

vm_brk_flags() can just call the do_mas_munmap() as it checks for
intersecting VMAs directly.

Link: https://lkml.kernel.org/r/20220906194824.2110408-29-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Tested-by: Yu Zhao <yuzhao@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 7 deletions

diff --git a/mm/mremap.c b/mm/mremap.c
index b522cd0259a0..e0fba9004246 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -975,20 +975,23 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 	/*
 	 * Always allow a shrinking remap: that just unmaps
 	 * the unnecessary pages..
-	 * __do_munmap does all the needed commit accounting, and
+	 * do_mas_munmap does all the needed commit accounting, and
 	 * downgrades mmap_lock to read if so directed.
 	 */
 	if (old_len >= new_len) {
 		int retval;
+		MA_STATE(mas, &mm->mm_mt, addr + new_len, addr + new_len);
 
-		retval = __do_munmap(mm, addr+new_len, old_len - new_len,
-				  &uf_unmap, true);
-		if (retval < 0 && old_len != new_len) {
-			ret = retval;
-			goto out;
+		retval = do_mas_munmap(&mas, mm, addr + new_len,
+				       old_len - new_len, &uf_unmap, true);
 		/* Returning 1 indicates mmap_lock is downgraded to read. */
-		} else if (retval == 1)
+		if (retval == 1) {
 			downgraded = true;
+		} else if (retval < 0 && old_len != new_len) {
+			ret = retval;
+			goto out;
+		}
+
 		ret = addr;
 		goto out;
 	}