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ANDROID: userfaultfd: add MOVE ioctl mode to confirm bug-fixes

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Following issues were reported in the MOVE ioctl:
1. Panic when trying to move a source page which is in swap-cache [1]
2. Livelock when multiple threads try to move the same source page [2]

Three patches have been upstreamed to fix these issues [3, 4, 5]

MOVE ioctl was backported to ACK 6.1 and 6.6 for ART GC to use it [6].
Therefore, on these kernels in order to be able to identify in the
userspace if the fixes are included, this mode is added.

NOTE: UFFDIO_MOVE_MODE_CONFIRM_FIXED mode is only for 6.1 and 6.6
kernels, and will go away afterwards.

[1] https://lore.kernel.org/linux-mm/20250219112519.92853-1-21cnbao@gmail.com/
[2] https://github.com/lokeshgidra/uffd_move_ioctl_deadlock
[3] https://web.git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-hotfixes-stable&id=c50f8e6053b0503375c2975bf47f182445aebb4c
[4] https://web.git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-hotfixes-stable&id=37b338eed10581784e854d4262da05c8d960c748
[5] https://web.git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?h=mm-hotfixes-stable&id=927e926d72d9155fde3264459fe9bfd7b5e40d28
[6] b/274911254

Bug: 401790618
Change-Id: Ibd854ec7ac9ae6a2ca416767d032b6c71f1bc688
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
This commit is contained in:
Lokesh Gidra
2025-03-10 19:17:57 +00:00
parent 8d8d44ff91
commit 9bcabbda67
2 changed files with 9 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
fs/userfaultfd.c
View File

@@ -1942,7 +1942,8 @@ static int userfaultfd_move(struct userfaultfd_ctx *ctx,
return ret; return ret;
if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES| if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
UFFDIO_MOVE_MODE_DONTWAKE)) UFFDIO_MOVE_MODE_DONTWAKE|
UFFDIO_MOVE_MODE_CONFIRM_FIXED))
return -EINVAL; return -EINVAL;
if (mmget_not_zero(mm)) { if (mmget_not_zero(mm)) {

7
include/uapi/linux/userfaultfd.h
View File

@@ -325,6 +325,13 @@ struct uffdio_move {
*/ */
#define UFFDIO_MOVE_MODE_DONTWAKE ((__u64)1<<0) #define UFFDIO_MOVE_MODE_DONTWAKE ((__u64)1<<0)
#define UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES ((__u64)1<<1) #define UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES ((__u64)1<<1)
/*
* To confirm if the ioctl has fixes to avoid panic when src folio is
* in swap-cache. Also, to avoid livelock when multiple threads try
* to move same src folio. It's a KMI workaround and cannot be relied
* upon by userspace.
*/
#define UFFDIO_MOVE_MODE_CONFIRM_FIXED ((__u64)1<<63)
__u64 mode; __u64 mode;
/* /*
* "move" is written by the ioctl and must be at the end: the * "move" is written by the ioctl and must be at the end: the