[003/131] mm/gup: move __get_user_pages_fast() down a few lines in gup.c

Commit Message

Andrew Morton June 3, 2020, 10:56 p.m. UTC

From: John Hubbard <[e-mail]>
Subject: 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.

Link: http://lkml.kernel.org/r/[e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: John Hubbard <[e-mail]>
Reviewed-by: Chris Wilson <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: "Joonas Lahtinen" <[e-mail]>
Cc: Matthew Auld <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Rodrigo Vivi <[e-mail]>
Cc: Souptick Joarder <[e-mail]>
Cc: Tvrtko Ursulin <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/gup.c |  132 ++++++++++++++++++++++++++---------------------------
 1 file changed, 66 insertions(+), 66 deletions(-)

Comments

John Hubbard June 4, 2020, 1:51 a.m. UTC | #1

On 2020-06-03 15:56, Andrew Morton wrote:
> From: John Hubbard <[e-mail]>
> Subject: 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.

These patches 003 through 007 (gup refactoring and pin_user_pages stuff) all
look good.

Thanks for fixing up the merge conflicts with commit
17839856fd58 ("gup: document and work around "COW can break either way" issue").
I wasn't aware of that commit until the -next conflict email showed up in
my inbox this morning.

thanks,

Patch

--- a/mm/gup.c~mm-gup-move-__get_user_pages_fast-down-a-few-lines-in-gupc
+++ a/mm/gup.c
@@ -2703,72 +2703,6 @@  static bool gup_fast_permitted(unsigned
 }
 #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(
 	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