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powerpc: Implement __get_user_pages_fast()

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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: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Paul Mackerras 2013-08-05 14:11:23 +10:00 committed by Benjamin Herrenschmidt
parent cb96143def
commit 1f7bf02876
1 changed files with 21 additions and 16 deletions
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37
arch/powerpc/mm/gup.c
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@ -117,8 +117,8 @@ 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,
struct page **pages)
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;
@ -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 ret;
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages)
{
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 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
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 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
else
ret += nr;
}
return ret;
}
return ret;
}
#endif /* __HAVE_ARCH_PTE_SPECIAL */