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mm/gup: Provide callback to check if __GUP_fast() is allowed for the range

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This is a preparation patch for the transition of x86 to the generic GUP_fast()
implementation.

On x86, get_user_pages_fast() does a couple of sanity checks to see if we can
call __get_user_pages_fast() for the range.

This kind of wrapping protection should be useful for the generic code too.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Aneesh Kumar K . V <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dann Frazier <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
[ Small readability edits. ]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Kirill A. Shutemov 2017-03-16 18:26:54 +03:00 • committed by Ingo Molnar
commit 73e10a6181
1 changed files with 21 additions and 3 deletions
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24
mm/gup.c
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@ -1614,6 +1614,21 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
return nr;
}
#ifndef gup_fast_permitted
/*
* Check if it's allowed to use __get_user_pages_fast() for the range, or
* we need to fall back to the slow version:
*/
bool gup_fast_permitted(unsigned long start, int nr_pages, int write)
{
unsigned long len, end;
len = (unsigned long) nr_pages << PAGE_SHIFT;
end = start + len;
return end >= start;
}
#endif
/**
* get_user_pages_fast() - pin user pages in memory
* @start: starting user address
@ -1633,11 +1648,14 @@ 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)
{
int nr, ret;
int nr = 0, ret = 0;
start &= PAGE_MASK;
nr = __get_user_pages_fast(start, nr_pages, write, pages);
ret = nr;
if (gup_fast_permitted(start, nr_pages, write)) {
nr = __get_user_pages_fast(start, nr_pages, write, pages);
ret = nr;
}
if (nr < nr_pages) {
/* Try to get the remaining pages with get_user_pages */