On Sun, 5 Feb 2017 10:46:29 -0800 Guenter Roeck [off-list ref] wrote:

On Fri, Jan 27, 2017 at 08:44:30PM +0200, Mike Rapoport wrote:

quoted

When a non-cooperative userfaultfd monitor copies pages in the background,
it may encounter regions that were already unmapped. Addition of
UFFD_EVENT_UNMAP allows the uffd monitor to track precisely changes in the
virtual memory layout.

Since there might be different uffd contexts for the affected VMAs, we
first should create a temporary representation for the unmap event for each
uffd context and then notify them one by one to the appropriate userfault
file descriptors.

The event notification occurs after the mmap_sem has been released.

Signed-off-by: Mike Rapoport <redacted>
Acked-by: Hillf Danton <redacted>

Just in case 0day didn't report it yet, this patch causes build errors
with various architectures.

mm/nommu.c:1201:15: error: conflicting types for 'do_mmap'
 unsigned long do_mmap(struct file *file,
               ^
In file included from mm/nommu.c:19:0:
	include/linux/mm.h:2095:22: note:
		previous declaration of 'do_mmap' was here

mm/nommu.c:1580:5: error: conflicting types for 'do_munmap'
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
    ^
In file included from mm/nommu.c:19:0:
	include/linux/mm.h:2099:12: note:
		previous declaration of 'do_munmap' was here

This was fixed in
http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-non-cooperative-add-event-for-memory-unmaps-fix.patch?

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