[PATCH] mm: fix faulting range in do_fault_around

[Konstantin Khlebnikov <k.khlebnikov@samsung.com>]

From: Konstantin Khlebnikov <koct9i@gmail.com>

do_fault_around shoudn't cross pmd boundaries.

This patch does calculation in terms of addresses rather than pgoff.
It looks much cleaner in this way. Probably it's worth to replace
vmf->max_pgoff with vmf->end_address as well.

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Reported-by: "Ingo Korb" <ingo.korb@tu-dortmund.de>
---
 mm/memory.c |   26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index d67fd9f..f27638a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2831,33 +2831,29 @@ late_initcall(fault_around_debugfs);
 static void do_fault_around(struct vm_area_struct *vma, unsigned long address,
 		pte_t *pte, pgoff_t pgoff, unsigned int flags)
 {
-	unsigned long start_addr;
+	unsigned long start_addr, end_addr;
 	pgoff_t max_pgoff;
 	struct vm_fault vmf;
 	int off;
 
-	start_addr = max(address & fault_around_mask(), vma->vm_start);
-	off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1);
+	start_addr = max3(vma->vm_start, address & PMD_MASK,
+			  address & fault_around_mask());
+
+	end_addr = min3(vma->vm_end, ALIGN(address, PMD_SIZE),
+			start_addr + PAGE_ALIGN(fault_around_bytes));
+
+	off = (address - start_addr) >> PAGE_SHIFT;
 	pte -= off;
 	pgoff -= off;
-
-	/*
-	 *  max_pgoff is either end of page table or end of vma
-	 *  or fault_around_pages() from pgoff, depending what is nearest.
-	 */
-	max_pgoff = pgoff - ((start_addr >> PAGE_SHIFT) & (PTRS_PER_PTE - 1)) +
-		PTRS_PER_PTE - 1;
-	max_pgoff = min3(max_pgoff, vma_pages(vma) + vma->vm_pgoff - 1,
-			pgoff + fault_around_pages() - 1);
+	max_pgoff = pgoff + ((end_addr - start_addr) >> PAGE_SHIFT) - 1;
 
 	/* Check if it makes any sense to call ->map_pages */
 	while (!pte_none(*pte)) {
-		if (++pgoff > max_pgoff)
-			return;
 		start_addr += PAGE_SIZE;
-		if (start_addr >= vma->vm_end)
+		if (start_addr >= end_addr)
 			return;
 		pte++;
+		pgoff++;
 	}
 
 	vmf.virtual_address = (void __user *) start_addr;

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