[PATCH 5.10 074/599] mm: madvise: skip unmapped vma holes passed to process_madvise

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 18:55:24 EST

From: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>

commit 08095d6310a7ce43256b4251577bc66a25c6e1a6 upstream.

The process_madvise() system call is expected to skip holes in vma passed
through 'struct iovec' vector list. But do_madvise, which
process_madvise() calls for each vma, returns ENOMEM in case of unmapped
holes, despite the VMA is processed.

Thus process_madvise() should treat ENOMEM as expected and consider the
VMA passed to as processed and continue processing other vma's in the
vector list. Returning -ENOMEM to user, despite the VMA is processed,
will be unable to figure out where to start the next madvise.

Link: https://lkml.kernel.org/r/4f091776142f2ebf7b94018146de72318474e686.1647008754.git.quic_charante@xxxxxxxxxxx
Fixes: ecb8ac8b1f14("mm/madvise: introduce process_madvise() syscall: an external memory hinting API")
Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
mm/madvise.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1222,9 +1222,16 @@ SYSCALL_DEFINE5(process_madvise, int, pi

while (iov_iter_count(&iter)) {
iovec = iov_iter_iovec(&iter);
+ /*
+ * do_madvise returns ENOMEM if unmapped holes are present
+ * in the passed VMA. process_madvise() is expected to skip
+ * unmapped holes passed to it in the 'struct iovec' list
+ * and not fail because of them. Thus treat -ENOMEM return
+ * from do_madvise as valid and continue processing.
+ */
ret = do_madvise(mm, (unsigned long)iovec.iov_base,
iovec.iov_len, behavior);
- if (ret < 0)
+ if (ret < 0 && ret != -ENOMEM)
iov_iter_advance(&iter, iovec.iov_len);