Commit 1f7bf028 authored by Paul Mackerras's avatar Paul Mackerras Committed by Benjamin Herrenschmidt
Browse files

powerpc: Implement __get_user_pages_fast() 



Other architectures have a __get_user_pages_fast(), in addition to the
regular get_user_pages_fast(), which doesn't call get_user_pages() on
failure, and thus doesn't attempt to fault pages in or COW them.  The
generic KVM code uses __get_user_pages_fast() to detect whether a page
for which we have only requested read access is actually writable.

This provides an implementation of __get_user_pages_fast() by
splitting the existing get_user_pages_fast() in two.  With this, the
generic KVM code will get the right answer instead of always
considering such pages non-writable.

Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent cb96143d

arch/powerpc/mm/gup.c

+21 −16
Original line number Diff line number Diff line
@@ -117,7 +117,7 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end, 
	return 1;

}



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

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

			  struct page **pages)

{

	struct mm_struct *mm = current->mm;
@@ -135,7 +135,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, 


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

					start, len)))

		goto slow_irqon;

		return 0;



	pr_devel("  aligned: %lx .. %lx\n", start, end);
@@ -166,30 +166,35 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, 
			 (void *)pgd_val(pgd));

		next = pgd_addr_end(addr, end);

		if (pgd_none(pgd))

			goto slow;

			break;

		if (pgd_huge(pgd)) {

			if (!gup_hugepte((pte_t *)pgdp, PGDIR_SIZE, addr, next,

					 write, pages, &nr))

				goto slow;

				break;

		} else if (is_hugepd(pgdp)) {

			if (!gup_hugepd((hugepd_t *)pgdp, PGDIR_SHIFT,

					addr, next, write, pages, &nr))

				goto slow;

				break;

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

			goto slow;

			break;

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



	local_irq_enable();



	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);

	return nr;

}



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

			struct page **pages)

{

		int ret;

	struct mm_struct *mm = current->mm;

	int nr, ret;



slow:

		local_irq_enable();

slow_irqon:

	start &= PAGE_MASK;

	nr = __get_user_pages_fast(start, nr_pages, write, pages);

	ret = nr;



	if (nr < nr_pages) {

		pr_devel("  slow path ! nr = %d\n", nr);



		/* Try to get the remaining pages with get_user_pages */
@@ -198,7 +203,7 @@ slow_irqon: 


		down_read(&mm->mmap_sem);

		ret = get_user_pages(current, mm, start,

			(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);

				     nr_pages - nr, write, 0, pages, NULL);

		up_read(&mm->mmap_sem);



		/* Have to be a bit careful with return values */
@@ -208,9 +213,9 @@ slow_irqon: 
			else

				ret += nr;

		}

	}



	return ret;

}

}



#endif /* __HAVE_ARCH_PTE_SPECIAL */

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