+ userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: userfaultfd: use ENOENT instead of EFAULT if the atomic copy user fails
has been added to the -mm tree.  Its filename is
     userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails.patch

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------------------------------------------------------
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: userfaultfd: use ENOENT instead of EFAULT if the atomic copy user fails

Patch series "userfaultfd shmem updates".

Jann found two bugs in the userfaultfd shmem MAP_SHARED backend: the lack
of the VM_MAYWRITE check and the lack of i_size checks.

Then looking into the above we also fixed the MAP_PRIVATE case.

Hugh by source review also found a data loss source if UFFDIO_COPY is used
on shmem MAP_SHARED PROT_READ mappings (the production usages incidentally
run with PROT_READ|PROT_WRITE, so the data loss couldn't happen in those
production usages like with QEMU).

The whole patchset is marked for stable.

We verified QEMU postcopy live migration with guest running on shmem
MAP_PRIVATE run as well as before after the fix of shmem MAP_PRIVATE. 
Regardless if it's shmem or hugetlbfs or MAP_PRIVATE or MAP_SHARED, QEMU
unconditionally invokes a punch hole if the guest mapping is filebacked
and a MADV_DONTNEED too (needed to get rid of the MAP_PRIVATE COWs and for
the anon backend).


This patch (of 5):

We internally used EFAULT to communicate with the caller, switch to
ENOENT, so EFAULT can be used as a non internal retval.

Link: http://lkml.kernel.org/r/20181126173452.26955-2-aarcange@redhat.com
Fixes: 4c27fe4c4c84 ("userfaultfd: shmem: add shmem_mcopy_atomic_pte for userfaultfd support")
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Hugh Dickins <hughd@google.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: <stable@vger.kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/mm/hugetlb.c~userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails
+++ a/mm/hugetlb.c
@@ -4080,7 +4080,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 
 		/* fallback to copy_from_user outside mmap_sem */
 		if (unlikely(ret)) {
-			ret = -EFAULT;
+			ret = -ENOENT;
 			*pagep = page;
 			/* don't free the page */
 			goto out;
--- a/mm/shmem.c~userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails
+++ a/mm/shmem.c
@@ -2238,7 +2238,7 @@ static int shmem_mfill_atomic_pte(struct
 				*pagep = page;
 				shmem_inode_unacct_blocks(inode, 1);
 				/* don't free the page */
-				return -EFAULT;
+				return -ENOENT;
 			}
 		} else {		/* mfill_zeropage_atomic */
 			clear_highpage(page);
--- a/mm/userfaultfd.c~userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails
+++ a/mm/userfaultfd.c
@@ -48,7 +48,7 @@ static int mcopy_atomic_pte(struct mm_st
 
 		/* fallback to copy_from_user outside mmap_sem */
 		if (unlikely(ret)) {
-			ret = -EFAULT;
+			ret = -ENOENT;
 			*pagep = page;
 			/* don't free the page */
 			goto out;
@@ -274,7 +274,7 @@ retry:
 
 		cond_resched();
 
-		if (unlikely(err == -EFAULT)) {
+		if (unlikely(err == -ENOENT)) {
 			up_read(&dst_mm->mmap_sem);
 			BUG_ON(!page);
 
@@ -530,7 +530,7 @@ retry:
 				       src_addr, &page, zeropage);
 		cond_resched();
 
-		if (unlikely(err == -EFAULT)) {
+		if (unlikely(err == -ENOENT)) {
 			void *page_kaddr;
 
 			up_read(&dst_mm->mmap_sem);
_

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

userfaultfd-use-enoent-instead-of-efault-if-the-atomic-copy-user-fails.patch
userfaultfd-shmem-allocate-anonymous-memory-for-map_private-shmem.patch
userfaultfd-shmem-hugetlbfs-only-allow-to-register-vm_maywrite-vmas.patch
userfaultfd-shmem-add-i_size-checks.patch
userfaultfd-shmem-uffdio_copy-set-the-page-dirty-if-vm_write-is-not-set.patch