[mm-unstable v7 12/18] mm/madvise: add MADV_COLLAPSE to process_madvise()

["Zach O'Keefe" <zokeefe@google.com>]

Allow MADV_COLLAPSE behavior for process_madvise(2) if caller has
CAP_SYS_ADMIN or is requesting collapse of it's own memory.

This is useful for the development of userspace agents that seek to
optimize THP utilization system-wide by using userspace signals to
prioritize what memory is most deserving of being THP-backed.

Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 mm/madvise.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 9f08e958ea86..6fb6b7160bda 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1171,13 +1171,15 @@ madvise_behavior_valid(int behavior)
 }
 
 static bool
-process_madvise_behavior_valid(int behavior)
+process_madvise_behavior_valid(int behavior, struct task_struct *task)
 {
 	switch (behavior) {
 	case MADV_COLD:
 	case MADV_PAGEOUT:
 	case MADV_WILLNEED:
 		return true;
+	case MADV_COLLAPSE:
+		return task == current || capable(CAP_SYS_ADMIN);
 	default:
 		return false;
 	}
@@ -1455,7 +1457,7 @@ SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
 		goto free_iov;
 	}
 
-	if (!process_madvise_behavior_valid(behavior)) {
+	if (!process_madvise_behavior_valid(behavior, task)) {
 		ret = -EINVAL;
 		goto release_task;
 	}
-- 
2.37.0.rc0.161.g10f37bed90-goog