FROMGIT: userfaultfd: disable huge PMD sharing for MINOR registered VMAs
As the comment says: for the MINOR fault use case, although the page might
be present and populated in the other (non-UFFD-registered) half of the
mapping, it may be out of date, and we explicitly want userspace to get a
minor fault so it can check and potentially update the page's contents.
Huge PMD sharing would prevent these faults from occurring for suitably
aligned areas, so disable it upon UFFD registration.
Link: https://lkml.kernel.org/r/20210301222728.176417-3-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Adam Ruprecht <ruprecht@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Cannon Matthews <cannonmatthews@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chinwen Chang <chinwen.chang@mediatek.com>
Cc: David Rientjes <rientjes@google.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Koutn" <mkoutny@suse.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oliver Upton <oupton@google.com>
Cc: Shaohua Li <shli@fb.com>
Cc: Shawn Anastasio <shawn@anastas.io>
Cc: Steven Price <steven.price@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
(cherry picked from commit 19fbec4445b6a690253c1785dfd376ede2cdb9d9
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm)
Link: https://lore.kernel.org/patchwork/patch/1388134/
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Bug: 160737021
Bug: 169683130
Change-Id: I257024f980f43cf8b06b5421ee3278115d1b1540
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index 1a00745..51cbfe4 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -47,12 +47,19 @@
}
/*
- * Never enable huge pmd sharing on uffd-wp registered vmas, because uffd-wp
- * protect information is per pgtable entry.
+ * Never enable huge pmd sharing on some uffd registered vmas:
+ *
+ * - VM_UFFD_WP VMAs, because write protect information is per pgtable entry.
+ *
+ * - VM_UFFD_MINOR VMAs, because otherwise we would never get minor faults for
+ * VMAs which share huge pmds. (If you have two mappings to the same
+ * underlying pages, and fault in the non-UFFD-registered one with a write,
+ * with huge pmd sharing this would *also* setup the second UFFD-registered
+ * mapping, and we'd not get minor faults.)
*/
static inline bool uffd_disable_huge_pmd_share(struct vm_area_struct *vma)
{
- return vma->vm_flags & VM_UFFD_WP;
+ return vma->vm_flags & (VM_UFFD_WP | VM_UFFD_MINOR);
}
static inline bool userfaultfd_missing(struct vm_area_struct *vma)