mm/gup: move __get_user_pages_fast() down a few lines in gup.c

Patch series "mm/gup, drm/i915: refactor gup_fast, convert to pin_user_pages()", v2.

In order to convert the drm/i915 driver from get_user_pages() to
pin_user_pages(), a FOLL_PIN equivalent of __get_user_pages_fast() was
required.  That led to refactoring __get_user_pages_fast(), with the
following goals:

1) As above: provide a pin_user_pages*() routine for drm/i915 to call,
   in place of __get_user_pages_fast(),

2) Get rid of the gup.c duplicate code for walking page tables with
   interrupts disabled. This duplicate code is a minor maintenance
   problem anyway.

3) Make it easy for an upcoming patch from Souptick, which aims to
   convert __get_user_pages_fast() to use a gup_flags argument, instead
   of a bool writeable arg.  Also, if this series looks good, we can
   ask Souptick to change the name as well, to whatever the consensus
   is. My initial recommendation is: get_user_pages_fast_only(), to
   match the new pin_user_pages_only().

This patch (of 4):

This is in order to avoid a forward declaration of
internal_get_user_pages_fast(), in the next patch.

This is code movement only--all generated code should be identical.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: "Joonas Lahtinen" <joonas.lahtinen@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://lkml.kernel.org/r/20200522051931.54191-1-jhubbard@nvidia.com
Link: http://lkml.kernel.org/r/20200519002124.2025955-1-jhubbard@nvidia.com
Link: http://lkml.kernel.org/r/20200519002124.2025955-2-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index 3edf740..57b5f3e 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2703,72 +2703,6 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
 }
 #endif
 
-/*
- * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
- * the regular GUP.
- * Note a difference with get_user_pages_fast: this always returns the
- * number of pages pinned, 0 if no pages were pinned.
- *
- * If the architecture does not support this function, simply return with no
- * pages pinned.
- *
- * Careful, careful! COW breaking can go either way, so a non-write
- * access can get ambiguous page results. If you call this function without
- * 'write' set, you'd better be sure that you're ok with that ambiguity.
- */
-int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
-                         struct page **pages)
-{
-       unsigned long len, end;
-       unsigned long flags;
-       int nr_pinned = 0;
-       /*
-        * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
-        * because gup fast is always a "pin with a +1 page refcount" request.
-        */
-       unsigned int gup_flags = FOLL_GET;
-
-       if (write)
-               gup_flags |= FOLL_WRITE;
-
-       start = untagged_addr(start) & PAGE_MASK;
-       len = (unsigned long) nr_pages << PAGE_SHIFT;
-       end = start + len;
-
-       if (end <= start)
-               return 0;
-       if (unlikely(!access_ok((void __user *)start, len)))
-               return 0;
-
-       /*
-        * Disable interrupts.  We use the nested form as we can already have
-        * interrupts disabled by get_futex_key.
-        *
-        * With interrupts disabled, we block page table pages from being
-        * freed from under us. See struct mmu_table_batch comments in
-        * include/asm-generic/tlb.h for more details.
-        *
-        * We do not adopt an rcu_read_lock(.) here as we also want to
-        * block IPIs that come from THPs splitting.
-        *
-        * NOTE! We allow read-only gup_fast() here, but you'd better be
-        * careful about possible COW pages. You'll get _a_ COW page, but
-        * not necessarily the one you intended to get depending on what
-        * COW event happens after this. COW may break the page copy in a
-        * random direction.
-        */
-
-       if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
-           gup_fast_permitted(start, end)) {
-               local_irq_save(flags);
-               gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
-               local_irq_restore(flags);
-       }
-
-       return nr_pinned;
-}
-EXPORT_SYMBOL_GPL(__get_user_pages_fast);
-
 static int __gup_longterm_unlocked(unsigned long start, int nr_pages,
                                   unsigned int gup_flags, struct page **pages)
 {
@@ -2848,6 +2782,72 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
        return ret;
 }
 
+/*
+ * Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
+ * the regular GUP.
+ * Note a difference with get_user_pages_fast: this always returns the
+ * number of pages pinned, 0 if no pages were pinned.
+ *
+ * If the architecture does not support this function, simply return with no
+ * pages pinned.
+ *
+ * Careful, careful! COW breaking can go either way, so a non-write
+ * access can get ambiguous page results. If you call this function without
+ * 'write' set, you'd better be sure that you're ok with that ambiguity.
+ */
+int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
+                         struct page **pages)
+{
+       unsigned long len, end;
+       unsigned long flags;
+       int nr_pinned = 0;
+       /*
+        * Internally (within mm/gup.c), gup fast variants must set FOLL_GET,
+        * because gup fast is always a "pin with a +1 page refcount" request.
+        */
+       unsigned int gup_flags = FOLL_GET;
+
+       if (write)
+               gup_flags |= FOLL_WRITE;
+
+       start = untagged_addr(start) & PAGE_MASK;
+       len = (unsigned long) nr_pages << PAGE_SHIFT;
+       end = start + len;
+
+       if (end <= start)
+               return 0;
+       if (unlikely(!access_ok((void __user *)start, len)))
+               return 0;
+
+       /*
+        * Disable interrupts.  We use the nested form as we can already have
+        * interrupts disabled by get_futex_key.
+        *
+        * With interrupts disabled, we block page table pages from being
+        * freed from under us. See struct mmu_table_batch comments in
+        * include/asm-generic/tlb.h for more details.
+        *
+        * We do not adopt an rcu_read_lock(.) here as we also want to
+        * block IPIs that come from THPs splitting.
+        *
+        * NOTE! We allow read-only gup_fast() here, but you'd better be
+        * careful about possible COW pages. You'll get _a_ COW page, but
+        * not necessarily the one you intended to get depending on what
+        * COW event happens after this. COW may break the page copy in a
+        * random direction.
+        */
+
+       if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
+           gup_fast_permitted(start, end)) {
+               local_irq_save(flags);
+               gup_pgd_range(start, end, gup_flags, pages, &nr_pinned);
+               local_irq_restore(flags);
+       }
+
+       return nr_pinned;
+}
+EXPORT_SYMBOL_GPL(__get_user_pages_fast);
+
 /**
  * get_user_pages_fast() - pin user pages in memory
  * @start:      starting user address