Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation"

This reverts commit 2947ba054a4dabbd82848728d765346886050029.

Dan Williams reported dax-pmem kernel warnings with the following signature:

   WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
   percpu ref (dax_pmem_percpu_release [dax_pmem]) <= 0 (0) after switching to atomic

... and bisected it to this commit, which suggests possible memory corruption
caused by the x86 fast-GUP conversion.

He also pointed out:

 "
  This is similar to the backtrace when we were not properly handling
  pud faults and was fixed with this commit: 220ced1676c4 "mm: fix
  get_user_pages() vs device-dax pud mappings"

  I've found some missing _devmap checks in the generic
  get_user_pages_fast() path, but this does not fix the regression
  [...]
 "

So given that there are known bugs, and a pretty robust looking bisection
points to this commit suggesting that are unknown bugs in the conversion
as well, revert it for the time being - we'll re-try in v4.13.

Reported-by: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: aneesh.kumar@linux.vnet.ibm.com
Cc: dann.frazier@canonical.com
Cc: dave.hansen@intel.com
Cc: steve.capper@linaro.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 53 deletions

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 942482a..f5af95a 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -244,11 +244,6 @@ static inline int pud_devmap(pud_t pud)
 	return 0;
 }
 #endif
-
-static inline int pgd_devmap(pgd_t pgd)
-{
-	return 0;
-}
 #endif
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 
@@ -1190,54 +1185,6 @@ static inline u16 pte_flags_pkey(unsigned long pte_flags)
 #endif
 }
 
-static inline bool __pkru_allows_pkey(u16 pkey, bool write)
-{
-	u32 pkru = read_pkru();
-
-	if (!__pkru_allows_read(pkru, pkey))
-		return false;
-	if (write && !__pkru_allows_write(pkru, pkey))
-		return false;
-
-	return true;
-}
-
-/*
- * 'pteval' can come from a PTE, PMD or PUD.  We only check
- * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
- * same value on all 3 types.
- */
-static inline bool __pte_access_permitted(unsigned long pteval, bool write)
-{
-	unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
-
-	if (write)
-		need_pte_bits |= _PAGE_RW;
-
-	if ((pteval & need_pte_bits) != need_pte_bits)
-		return 0;
-
-	return __pkru_allows_pkey(pte_flags_pkey(pteval), write);
-}
-
-#define pte_access_permitted pte_access_permitted
-static inline bool pte_access_permitted(pte_t pte, bool write)
-{
-	return __pte_access_permitted(pte_val(pte), write);
-}
-
-#define pmd_access_permitted pmd_access_permitted
-static inline bool pmd_access_permitted(pmd_t pmd, bool write)
-{
-	return __pte_access_permitted(pmd_val(pmd), write);
-}
-
-#define pud_access_permitted pud_access_permitted
-static inline bool pud_access_permitted(pud_t pud, bool write)
-{
-	return __pte_access_permitted(pud_val(pud), write);
-}
-
 #include <asm-generic/pgtable.h>
 #endif	/* __ASSEMBLY__ */