Patch "userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE" has been added to the 4.4-stable tree

Patch "userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     userfaultfd-shmem-__do_fault-requires-vm_fault_nopage.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Mon Dec 18 14:47:43 CET 2017
From: Andrea Arcangeli <aarcange@redhat.com>
Date: Thu, 9 Mar 2017 16:16:28 -0800
Subject: userfaultfd: shmem: __do_fault requires VM_FAULT_NOPAGE

From: Andrea Arcangeli <aarcange@redhat.com>


[ Upstream commit 6bbc4a4144b1a69743022ac68dfaf6e7d993abb9 ]

__do_fault assumes vmf->page has been initialized and is valid if
VM_FAULT_NOPAGE is not returned by vma->vm_ops->fault(vma, vmf).

handle_userfault() in turn should return VM_FAULT_NOPAGE if it doesn't
return VM_FAULT_SIGBUS or VM_FAULT_RETRY (the other two possibilities).

This VM_FAULT_NOPAGE case is only invoked when signal are pending and it
didn't matter for anonymous memory before.  It only started to matter
since shmem was introduced.  hugetlbfs also takes a different path and
doesn't exercise __do_fault.

Link: http://lkml.kernel.org/r/20170228154201.GH5816@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/userfaultfd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -386,7 +386,7 @@ int handle_userfault(struct vm_area_stru
 			 * in such case.
 			 */
 			down_read(&mm->mmap_sem);
-			ret = 0;
+			ret = VM_FAULT_NOPAGE;
 		}
 	}
 


Patches currently in stable-queue which might be from aarcange@redhat.com are

queue-4.4/userfaultfd-selftest-vm-allow-to-build-in-vm-directory.patch
queue-4.4/userfaultfd-shmem-__do_fault-requires-vm_fault_nopage.patch