Commit 73e10a61 authored Mar 16, 2017 by Kirill A. Shutemov Committed by Ingo Molnar Mar 18, 2017

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>

parent b59f65fa

mm/gup.c

+21 −3

Original line number	Diff line number	Diff line
		@@ -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;

		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 */