mm: simplify gup_fast_permitted

Pass in the already calculated end value instead of recomputing it, and
leave the end > start check in the callers instead of duplicating them in
the arch code.

Link: http://lkml.kernel.org/r/20190625143715.1689-3-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David Miller <davem@davemloft.net>
Cc: James Hogan <jhogan@kernel.org>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/s390/include/asm/pgtable.h

@@ -1270,14 +1270,8 @@ static inline pte_t *pte_offset(pmd_t *pmd, unsigned long address)
 #define pte_offset_map(pmd, address) pte_offset_kernel(pmd, address)
 #define pte_unmap(pte) do { } while (0)
 
-static inline bool gup_fast_permitted(unsigned long start, int nr_pages)
+static inline bool gup_fast_permitted(unsigned long start, unsigned long end)
 {
-	unsigned long len, end;
-
-	len = (unsigned long) nr_pages << PAGE_SHIFT;
-	end = start + len;
-	if (end < start)
-		return false;
 	return end <= current->mm->context.asce_limit;
 }
 #define gup_fast_permitted gup_fast_permitted

arch/x86/include/asm/pgtable_64.h

@@ -259,14 +259,8 @@ extern void init_extra_mapping_uc(unsigned long phys, unsigned long size);
 extern void init_extra_mapping_wb(unsigned long phys, unsigned long size);
 
 #define gup_fast_permitted gup_fast_permitted
-static inline bool gup_fast_permitted(unsigned long start, int nr_pages)
+static inline bool gup_fast_permitted(unsigned long start, unsigned long end)
 {
-	unsigned long len, end;
-
-	len = (unsigned long)nr_pages << PAGE_SHIFT;
-	end = start + len;
-	if (end < start)
-		return false;
 	if (end >> __VIRTUAL_MASK_SHIFT)
 		return false;
 	return true;

mm/gup.c

@@ -2123,13 +2123,9 @@ static void gup_pgd_range(unsigned long addr, unsigned long end,
  * Check if it's allowed to use __get_user_pages_fast() for the range, or
  * we need to fall back to the slow version:
  */
-bool gup_fast_permitted(unsigned long start, int nr_pages)
+static bool gup_fast_permitted(unsigned long start, unsigned long end)
 {
-	unsigned long len, end;
-
-	len = (unsigned long) nr_pages << PAGE_SHIFT;
-	end = start + len;
-	return end >= start;
+	return true;
 }
 #endif
 
@@ -2150,6 +2146,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	len = (unsigned long) nr_pages << PAGE_SHIFT;
 	end = start + len;
 
+	if (end <= start)
+		return 0;
 	if (unlikely(!access_ok((void __user *)start, len)))
 		return 0;
 
@@ -2165,7 +2163,7 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	 * block IPIs that come from THPs splitting.
 	 */
 
-	if (gup_fast_permitted(start, nr_pages)) {
+	if (gup_fast_permitted(start, end)) {
 		local_irq_save(flags);
 		gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr);
 		local_irq_restore(flags);
@@ -2224,13 +2222,12 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
 	len = (unsigned long) nr_pages << PAGE_SHIFT;
 	end = start + len;
 
-	if (nr_pages <= 0)
+	if (end <= start)
 		return 0;
-
 	if (unlikely(!access_ok((void __user *)start, len)))
 		return -EFAULT;
 
-	if (gup_fast_permitted(start, nr_pages)) {
+	if (gup_fast_permitted(start, end)) {
 		local_irq_disable();
 		gup_pgd_range(addr, end, gup_flags, pages, &nr);
 		local_irq_enable();