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Commit 465a454f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

x86, mm: Add __get_user_pages_fast() 



Introduce a gup_fast() variant which is usable from IRQ/NMI context.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
CC: Nick Piggin <npiggin@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 75f937f2

arch/x86/mm/gup.c

+56 −0
Original line number Diff line number Diff line
@@ -219,6 +219,62 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, 
	return 1;

}



/*

 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall

 * back to the regular GUP.

 */

int __get_user_pages_fast(unsigned long start, int nr_pages, int write,

			  struct page **pages)

{

	struct mm_struct *mm = current->mm;

	unsigned long addr, len, end;

	unsigned long next;

	unsigned long flags;

	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,

					(void __user *)start, len)))

		return 0;



	/*

	 * XXX: batch / limit 'nr', to avoid large irq off latency

	 * needs some instrumenting to determine the common sizes used by

	 * important workloads (eg. DB2), and whether limiting the batch size

	 * will decrease performance.

	 *

	 * It seems like we're in the clear for the moment. Direct-IO is

	 * the main guy that batches up lots of get_user_pages, and even

	 * they are limited to 64-at-a-time which is not so many.

	 */

	/*

	 * This doesn't prevent pagetable teardown, but does prevent

	 * the pagetables and pages from being freed on x86.

	 *

	 * So long as we atomically load page table pointers versus teardown

	 * (which we do on x86, with the above PAE exception), we can follow the

	 * address down to the the page and take a ref on it.

	 */

	local_irq_save(flags);

	pgdp = pgd_offset(mm, addr);

	do {

		pgd_t pgd = *pgdp;



		next = pgd_addr_end(addr, end);

		if (pgd_none(pgd))

			break;

		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))

			break;

	} while (pgdp++, addr = next, addr != end);

	local_irq_restore(flags);



	return nr;

}



/**

 * get_user_pages_fast() - pin user pages in memory

 * @start:	starting user address

include/linux/mm.h

+6 −0
Original line number Diff line number Diff line
@@ -862,6 +862,12 @@ extern int mprotect_fixup(struct vm_area_struct *vma, 
int get_user_pages_fast(unsigned long start, int nr_pages, int write,

			struct page **pages);



/*

 * doesn't attempt to fault and will return short.

 */

int __get_user_pages_fast(unsigned long start, int nr_pages, int write,

			  struct page **pages);



/*

 * A callback you can register to apply pressure to ageable caches.

 *