mm/gup: do not migrate zero page

On some platforms ZERO_PAGE(0) might end-up in a movable zone.  Do not
migrate zero page in gup during longterm pinning as migration of zero page
is not allowed.

For example, in x86 QEMU with 16G of memory and kernelcore=5G parameter, I
see the following:

Boot#1: zero_pfn  0x48a8d zero_pfn zone: ZONE_DMA32
Boot#2: zero_pfn 0x20168d zero_pfn zone: ZONE_MOVABLE

On x86, empty_zero_page is declared in .bss and depending on the loader
may end up in different physical locations during boots.

Also, move is_zero_pfn() my_zero_pfn() functions under CONFIG_MMU, because
zero_pfn that they are using is declared in memory.c which is compiled
with CONFIG_MMU.

Link: https://lkml.kernel.org/r/20210215161349.246722-9-pasha.tatashin@soleen.com
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Tyler Hicks <tyhicks@linux.microsoft.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mm.h b/include/linux/mm.h
index d0e628f511e433554d3829fd5fa8a15f7a1d56b1..76e27ebb28a39759b331ea747c7f8bcd4ad0496d 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1559,7 +1559,8 @@ static inline unsigned long page_to_section(const struct page *page)
 #ifdef CONFIG_MIGRATION
 static inline bool is_pinnable_page(struct page *page)
 {
-       return !is_zone_movable_page(page) && !is_migrate_cma_page(page);
+       return !(is_zone_movable_page(page) || is_migrate_cma_page(page)) ||
+               is_zero_pfn(page_to_pfn(page));
 }
 #else
 static inline bool is_pinnable_page(struct page *page)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 3b22057410482611507cccc60b5fe57d4a90fed2..92b44149d5b9dcd1eccf4194e0703ef3536fd92c 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -427,6 +427,10 @@ enum zone_type {
         *    techniques might use alloc_contig_range() to hide previously
         *    exposed pages from the buddy again (e.g., to implement some sort
         *    of memory unplug in virtio-mem).
+        * 6. ZERO_PAGE(0), kernelcore/movablecore setups might create
+        *    situations where ZERO_PAGE(0) which is allocated differently
+        *    on different platforms may end up in a movable zone. ZERO_PAGE(0)
+        *    cannot be migrated.
         *
         * In general, no unmovable allocations that degrade memory offlining
         * should end up in ZONE_MOVABLE. Allocators (like alloc_contig_range())

diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 5e772392a379560d2cc7dffc02227fcc0c604559..2194a9cd885cff54a337e3b5918935439cb69062 100644 (file)
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1111,6 +1111,7 @@ extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
 extern void untrack_pfn_moved(struct vm_area_struct *vma);
 #endif
 
+#ifdef CONFIG_MMU
 #ifdef __HAVE_COLOR_ZERO_PAGE
 static inline int is_zero_pfn(unsigned long pfn)
 {
@@ -1134,6 +1135,17 @@ static inline unsigned long my_zero_pfn(unsigned long addr)
        return zero_pfn;
 }
 #endif
+#else
+static inline int is_zero_pfn(unsigned long pfn)
+{
+       return 0;
+}
+
+static inline unsigned long my_zero_pfn(unsigned long addr)
+{
+       return 0;
+}
+#endif /* CONFIG_MMU */
 
 #ifdef CONFIG_MMU