mm/migrate: convert do_pages_stat_array() from follow_page() to folio_walk

Let's use folio_walk instead, so we can avoid taking a folio reference
just to read the nid and get rid of another follow_page()/FOLL_DUMP user.
Use FW_ZEROPAGE so we can return "-EFAULT" for it as documented.

The possible return values for follow_page() were confusing, especially
with FOLL_DUMP set.  We'll handle it like documented in the man page:

* -EFAULT: This is a zero page or the memory area is not mapped by the
   process.
* -ENOENT: The page is not present.

We'll keep setting -ENOENT for ZONE_DEVICE.  Maybe not the right thing to
do, but it likely doesn't really matter (just like for weird devmap,
whereby we fake "not present").

Note that the other errors (-EACCESS, -EBUSY, -EIO, -EINVAL, -ENOMEM) so
far only applied when actually moving pages, not when only querying stats.

We'll effectively drop the "secretmem" check we had in follow_page(), but
that shouldn't really matter here, we're not accessing folio/page content
after all.

Link: https://lkml.kernel.org/r/20240802155524.517137-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/migrate.c b/mm/migrate.c
index aa482c954cb0486c03abecd04b708d09f25ce507..b5365a434ba9964e2d267941e8bc3b313b1d59c1 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -50,6 +50,7 @@
 #include <linux/random.h>
 #include <linux/sched/sysctl.h>
 #include <linux/memory-tiers.h>
+#include <linux/pagewalk.h>
 
 #include <asm/tlbflush.h>
 
@@ -2331,28 +2332,26 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
        for (i = 0; i < nr_pages; i++) {
                unsigned long addr = (unsigned long)(*pages);
                struct vm_area_struct *vma;
-               struct page *page;
+               struct folio_walk fw;
+               struct folio *folio;
                int err = -EFAULT;
 
                vma = vma_lookup(mm, addr);
                if (!vma)
                        goto set_status;
 
-               /* FOLL_DUMP to ignore special (like zero) pages */
-               page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
-
-               err = PTR_ERR(page);
-               if (IS_ERR(page))
-                       goto set_status;
-
-               err = -ENOENT;
-               if (!page)
-                       goto set_status;
-
-               if (!is_zone_device_page(page))
-                       err = page_to_nid(page);
-
-               put_page(page);
+               folio = folio_walk_start(&fw, vma, addr, FW_ZEROPAGE);
+               if (folio) {
+                       if (is_zero_folio(folio) || is_huge_zero_folio(folio))
+                               err = -EFAULT;
+                       else if (folio_is_zone_device(folio))
+                               err = -ENOENT;
+                       else
+                               err = folio_nid(folio);
+                       folio_walk_end(&fw, vma);
+               } else {
+                       err = -ENOENT;
+               }
 set_status:
                *status = err;