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

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 <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aneesh Kumar K . V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dann Frazier <dann.frazier@canonical.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20170316152655.37789-7-kirill.shutemov@linux.intel.com
[ Small readability edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kirill A. Shutemov 2017-03-16 18:26:54 +03:00 committed by Ingo Molnar
parent b59f65fa07
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; 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 * get_user_pages_fast() - pin user pages in memory
* @start: starting user address * @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, int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages) struct page **pages)
{ {
int nr, ret; int nr = 0, ret = 0;
start &= PAGE_MASK; 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) { if (nr < nr_pages) {
/* Try to get the remaining pages with get_user_pages */ /* Try to get the remaining pages with get_user_pages */