x86/mm/gup: Simplify get_user_pages() PTE bit handling

The current get_user_pages() code is a wee bit more complicated
than it needs to be for pte bit checking.  Currently, it establishes
a mask of required pte _PAGE_* bits and ensures that the pte it
goes after has all those bits.

This consolidates the three identical copies of this code.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20160212210218.3A2D4045@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 22 insertions, 16 deletions

diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index ce5e4545203b..2f0a32945cda 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -75,6 +75,24 @@ static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
 }
 
 /*
+ * '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 int pte_allows_gup(unsigned long pteval, int 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 1;
+}
+
+/*
  * The performance critical leaf functions are made noinline otherwise gcc
  * inlines everything into a single function which results in too much
  * register pressure.
@@ -83,14 +101,9 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
                 unsigned long end, int write, struct page **pages, int *nr)
 {
         struct dev_pagemap *pgmap = NULL;
-        unsigned long mask;
         int nr_start = *nr;
         pte_t *ptep;
 
-        mask = _PAGE_PRESENT|_PAGE_USER;
-        if (write)
-                mask |= _PAGE_RW;
-
         ptep = pte_offset_map(&pmd, addr);
         do {
                 pte_t pte = gup_get_pte(ptep);
@@ -110,7 +123,8 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
                                 pte_unmap(ptep);
                                 return 0;
                         }
-                } else if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
+                } else if (!pte_allows_gup(pte_val(pte), write) ||
+                           pte_special(pte)) {
                         pte_unmap(ptep);
                         return 0;
                 }
@@ -164,14 +178,10 @@ static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
 static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
                 unsigned long end, int write, struct page **pages, int *nr)
 {
-        unsigned long mask;
         struct page *head, *page;
         int refs;
 
-        mask = _PAGE_PRESENT|_PAGE_USER;
-        if (write)
-                mask |= _PAGE_RW;
-        if ((pmd_flags(pmd) & mask) != mask)
+        if (!pte_allows_gup(pmd_val(pmd), write))
                 return 0;
 
         VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
@@ -231,14 +241,10 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
 static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
                 unsigned long end, int write, struct page **pages, int *nr)
 {
-        unsigned long mask;
         struct page *head, *page;
         int refs;
 
-        mask = _PAGE_PRESENT|_PAGE_USER;
-        if (write)
-                mask |= _PAGE_RW;
-        if ((pud_flags(pud) & mask) != mask)
+        if (!pte_allows_gup(pud_val(pud), write))
                 return 0;
         /* hugepages are never "special" */
         VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL);