Messages in this thread Patch in this message | | | From | David Hildenbrand <> | Subject | [PATCH v3 5/6] virtio-mem: use page_offline_(start|end) when setting PageOffline() | Date | Wed, 26 May 2021 11:30:40 +0200 |
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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.
Acked-by: Michael S. Tsirkin <mst@redhat.com> Acked-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: Oscar Salvador <osalvador@suse.de> Signed-off-by: David Hildenbrand <david@redhat.com> --- drivers/virtio/virtio_mem.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c index 10ec60d81e84..dc2a2e2b2ff8 100644 --- a/drivers/virtio/virtio_mem.c +++ b/drivers/virtio/virtio_mem.c @@ -1065,6 +1065,7 @@ static int virtio_mem_memory_notifier_cb(struct notifier_block *nb, 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(unsigned long pfn, ClearPageReserved(page); } } + page_offline_end(); } /* -- 2.31.1
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