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Subject[PATCH 4.14 06/95] mm: fix device-dax pud write-faults triggered by get_user_pages()
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@intel.com>

commit 1501899a898dfb5477c55534bdfd734c046da06d upstream.

Currently only get_user_pages_fast() can safely handle the writable gup
case due to its use of pud_access_permitted() to check whether the pud
entry is writable. In the gup slow path pud_write() is used instead of
pud_access_permitted() and to date it has been unimplemented, just calls
BUG_ON().

kernel BUG at ./include/linux/hugetlb.h:244!
[..]
RIP: 0010:follow_devmap_pud+0x482/0x490
[..]
Call Trace:
follow_page_mask+0x28c/0x6e0
__get_user_pages+0xe4/0x6c0
get_user_pages_unlocked+0x130/0x1b0
get_user_pages_fast+0x89/0xb0
iov_iter_get_pages_alloc+0x114/0x4a0
nfs_direct_read_schedule_iovec+0xd2/0x350
? nfs_start_io_direct+0x63/0x70
nfs_file_direct_read+0x1e0/0x250
nfs_file_read+0x90/0xc0

For now this just implements a simple check for the _PAGE_RW bit similar
to pmd_write. However, this implies that the gup-slow-path check is
missing the extra checks that the gup-fast-path performs with
pud_access_permitted. Later patches will align all checks to use the
'access_permitted' helper if the architecture provides it.

Note that the generic 'access_permitted' helper fallback is the simple
_PAGE_RW check on architectures that do not define the
'access_permitted' helper(s).

[dan.j.williams@intel.com: fix powerpc compile error]
Link: http://lkml.kernel.org/r/151129126165.37405.16031785266675461397.stgit@dwillia2-desk3.amr.corp.intel.com
Link: http://lkml.kernel.org/r/151043109938.2842.14834662818213616199.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Thomas Gleixner <tglx@linutronix.de> [x86]
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/pgtable.h | 6 ++++++
include/asm-generic/pgtable.h | 8 ++++++++
include/linux/hugetlb.h | 8 --------
3 files changed, 14 insertions(+), 8 deletions(-)

--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -1093,6 +1093,12 @@ static inline void pmdp_set_wrprotect(st
clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp);
}

+#define pud_write pud_write
+static inline int pud_write(pud_t pud)
+{
+ return pud_flags(pud) & _PAGE_RW;
+}
+
/*
* clone_pgd_range(pgd_t *dst, pgd_t *src, int count);
*
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -814,6 +814,14 @@ static inline int pmd_write(pmd_t pmd)
#endif /* __HAVE_ARCH_PMD_WRITE */
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

+#ifndef pud_write
+static inline int pud_write(pud_t pud)
+{
+ BUG();
+ return 0;
+}
+#endif /* pud_write */
+
#if !defined(CONFIG_TRANSPARENT_HUGEPAGE) || \
(defined(CONFIG_TRANSPARENT_HUGEPAGE) && \
!defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD))
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -239,14 +239,6 @@ static inline int pgd_write(pgd_t pgd)
}
#endif

-#ifndef pud_write
-static inline int pud_write(pud_t pud)
-{
- BUG();
- return 0;
-}
-#endif
-
#define HUGETLB_ANON_FILE "anon_hugepage"

enum {

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