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Commit 9b79022c authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Fix 'get_user_pages_fast()' with non-page-aligned start address 



Alexey Dobriyan reported trouble with LTP with the new fast-gup code,
and Johannes Weiner debugged it to non-page-aligned addresses, where the
new get_user_pages_fast() code would do all the wrong things, including
just traversing past the end of the requested area due to 'addr' never
matching 'end' exactly.

This is not a pretty fix, and we may actually want to move the alignment
into generic code, leaving just the core code per-arch, but Alexey
verified that the vmsplice01 LTP test doesn't crash with this.

Reported-and-tested-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
Debugged-by: default avatarJohannes Weiner <hannes@saeurebad.de>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 34ee5501

arch/x86/mm/gup.c

+6 −3
Original line number Diff line number Diff line
@@ -223,14 +223,17 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, 
			struct page **pages)

{

	struct mm_struct *mm = current->mm;

	unsigned long end = start + (nr_pages << PAGE_SHIFT);

	unsigned long addr = start;

	unsigned long addr, len, end;

	unsigned long next;

	pgd_t *pgdp;

	int nr = 0;



	start &= PAGE_MASK;

	addr = start;

	len = (unsigned long) nr_pages << PAGE_SHIFT;

	end = start + len;

	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,

					start, nr_pages*PAGE_SIZE)))

					start, len)))

		goto slow_irqon;



	/*