+ virtio-mem-use-page_offline_startend-when-setting-pageoffline.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: virtio-mem: use page_offline_(start|end) when setting PageOffline()
has been added to the -mm tree.  Its filename is
     virtio-mem-use-page_offline_startend-when-setting-pageoffline.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/virtio-mem-use-page_offline_startend-when-setting-pageoffline.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/virtio-mem-use-page_offline_startend-when-setting-pageoffline.patch

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------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: virtio-mem: use page_offline_(start|end) when setting PageOffline()

Let's properly use page_offline_(start|end) to synchronize setting
PageOffline(), so we won't have valid page access to unplugged memory
regions from /proc/kcore.

Existing balloon implementations usually allow reading inflated memory;
doing so might result in unnecessary overhead in the hypervisor, which is
currently the case with virtio-mem.

For future virtio-mem use cases, it will be different when using shmem,
huge pages, !anonymous private mappings, ...  as backing storage for a VM.
virtio-mem unplugged memory must no longer be accessed and access might
result in undefined behavior.  There will be a virtio spec extension to
document this change, including a new feature flag indicating the changed
behavior.  We really don't want to race against PFN walkers reading random
page content.

Link: https://lkml.kernel.org/r/20210526093041.8800-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-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: Michal Hocko <mhocko@suse.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>
---

 drivers/virtio/virtio_mem.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/virtio/virtio_mem.c~virtio-mem-use-page_offline_startend-when-setting-pageoffline
+++ a/drivers/virtio/virtio_mem.c
@@ -1065,6 +1065,7 @@ static int virtio_mem_memory_notifier_cb
 static void virtio_mem_set_fake_offline(unsigned long pfn,
 					unsigned long nr_pages, bool onlined)
 {
+	page_offline_begin();
 	for (; nr_pages--; pfn++) {
 		struct page *page = pfn_to_page(pfn);
 
@@ -1075,6 +1076,7 @@ static void virtio_mem_set_fake_offline(
 			ClearPageReserved(page);
 		}
 	}
+	page_offline_end();
 }
 
 /*
_

Patches currently in -mm which might be from david@redhat.com are

perf-map_executable-does-not-indicate-vm_mayexec.patch
binfmt-remove-in-tree-usage-of-map_executable.patch
mm-ignore-map_executable-in-ksys_mmap_pgoff.patch
fs-proc-kcore-drop-kcore_remap-and-kcore_other.patch
fs-proc-kcore-pfn_is_ram-check-only-applies-to-kcore_ram.patch
fs-proc-kcore-dont-read-offline-sections-logically-offline-pages-and-hwpoisoned-pages.patch
mm-introduce-page_offline_beginendfreezethaw-to-synchronize-setting-pageoffline.patch
virtio-mem-use-page_offline_startend-when-setting-pageoffline.patch
fs-proc-kcore-use-page_offline_freezethaw.patch
mm-make-variable-names-for-populate_vma_page_range-consistent.patch
mm-madvise-introduce-madv_populate_readwrite-to-prefault-page-tables.patch
maintainers-add-tools-testing-selftests-vm-to-memory-management.patch
selftests-vm-add-protection_keys_32-protection_keys_64-to-gitignore.patch
selftests-vm-add-test-for-madv_populate_readwrite.patch
memory-hotplugrst-complete-admin-guide-overhaul.patch