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authorDavid Hildenbrand <david@redhat.com>2021-07-01 04:50:14 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-07-01 06:47:28 +0300
commit82840451936f0301781ece80322230fd8edfc648 (patch)
tree0566617b1a69a661f59dfeba39f9a065871c89a5 /include/linux/page-flags.h
parent0daa322b8ff94d8ee4081c2c6868a1aaf1309642 (diff)
downloadlinux-82840451936f0301781ece80322230fd8edfc648.tar.xz
mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline()
A driver might set a page logically offline -- PageOffline() -- and turn the page inaccessible in the hypervisor; after that, access to page content can be fatal. One example is virtio-mem; while unplugged memory -- marked as PageOffline() can currently be read in the hypervisor, this will no longer be the case in the future; for example, when having a virtio-mem device backed by huge pages in the hypervisor. Some special PFN walkers -- i.e., /proc/kcore -- read content of random pages after checking PageOffline(); however, these PFN walkers can race with drivers that set PageOffline(). Let's introduce page_offline_(begin|end|freeze|thaw) for synchronizing. page_offline_freeze()/page_offline_thaw() allows for a subsystem to synchronize with such drivers, achieving that a page cannot be set PageOffline() while frozen. page_offline_begin()/page_offline_end() is used by drivers that care about such races when setting a page PageOffline(). For simplicity, use a rwsem for now; neither drivers nor users are performance sensitive. Link: https://lkml.kernel.org/r/20210526093041.8800-5-david@redhat.com Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Michal Hocko <mhocko@suse.com> Reviewed-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Cc: Aili Yao <yaoaili@kingsoft.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Alex Shi <alex.shi@linux.alibaba.com> Cc: Haiyang Zhang <haiyangz@microsoft.com> Cc: Jason Wang <jasowang@redhat.com> Cc: Jiri Bohac <jbohac@suse.cz> Cc: "K. Y. Srinivasan" <kys@microsoft.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com> Cc: Roman Gushchin <guro@fb.com> Cc: Stephen Hemminger <sthemmin@microsoft.com> Cc: Steven Price <steven.price@arm.com> Cc: Wei Liu <wei.liu@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/page-flags.h')
-rw-r--r--include/linux/page-flags.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 613295588848..3e7e616067fc 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -769,9 +769,19 @@ PAGE_TYPE_OPS(Buddy, buddy)
* relies on this feature is aware that re-onlining the memory block will
* require to re-set the pages PageOffline() and not giving them to the
* buddy via online_page_callback_t.
+ *
+ * There are drivers that mark a page PageOffline() and expect there won't be
+ * any further access to page content. PFN walkers that read content of random
+ * pages should check PageOffline() and synchronize with such drivers using
+ * page_offline_freeze()/page_offline_thaw().
*/
PAGE_TYPE_OPS(Offline, offline)
+extern void page_offline_freeze(void);
+extern void page_offline_thaw(void);
+extern void page_offline_begin(void);
+extern void page_offline_end(void);
+
/*
* Marks pages in use as page tables.
*/