| Message ID | 20210514172247.176750-6-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages | expand |
On Fri, May 14, 2021 at 07:22:46PM +0200, David Hildenbrand wrote: > 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> > 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 > >
On Fri, May 14, 2021 at 07:22:46PM +0200, David Hildenbrand wrote: > 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> > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Oscar Salvador <osalvador@suse.de>
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(); } /*