search for: refocunt

...e __put_page() change is necessary > for the following race I identified: > > Page has a refcount of 1 (e.g., allocated by virtio-mem using > alloc_contig_range()). > > a) kernel: get_page_unless_zero(page): refcount = 2 > b) virtio-mem: set page PG_offline, reduce refcount): refocunt = 1 > c) kernel: put_page(page): refcount = 0 > > The page would suddenly be given to the buddy. which is bad. But why cannot you keep the reference count at 1 (do get_page when offlining the page)? In other words as long as the driver knows the page has been returned to the host then it...

...e __put_page() change is necessary > for the following race I identified: > > Page has a refcount of 1 (e.g., allocated by virtio-mem using > alloc_contig_range()). > > a) kernel: get_page_unless_zero(page): refcount = 2 > b) virtio-mem: set page PG_offline, reduce refcount): refocunt = 1 > c) kernel: put_page(page): refcount = 0 > > The page would suddenly be given to the buddy. which is bad. But why cannot you keep the reference count at 1 (do get_page when offlining the page)? In other words as long as the driver knows the page has been returned to the host then it...

...rgot to answer this questions. The __put_page() change is necessary for the following race I identified: Page has a refcount of 1 (e.g., allocated by virtio-mem using alloc_contig_range()). a) kernel: get_page_unless_zero(page): refcount = 2 b) virtio-mem: set page PG_offline, reduce refcount): refocunt = 1 c) kernel: put_page(page): refcount = 0 The page would suddenly be given to the buddy. which is bad. -- Thanks, David / dhildenb

...ecessary >> for the following race I identified: >> >> Page has a refcount of 1 (e.g., allocated by virtio-mem using >> alloc_contig_range()). >> >> a) kernel: get_page_unless_zero(page): refcount = 2 >> b) virtio-mem: set page PG_offline, reduce refcount): refocunt = 1 >> c) kernel: put_page(page): refcount = 0 >> >> The page would suddenly be given to the buddy. which is bad. > > But why cannot you keep the reference count at 1 (do get_page when > offlining the page)? In other words as long as the driver knows the page > has be...

On Thu 19-09-19 16:22:25, David Hildenbrand wrote: > virtio-mem wants to allow to offline memory blocks of which some parts > were unplugged, especially, to later offline and remove completely > unplugged memory blocks. The important part is that PageOffline() has > to remain set until the section is offline, so these pages will never > get accessed (e.g., when dumping). The pages

On Thu 19-09-19 16:22:25, David Hildenbrand wrote: > virtio-mem wants to allow to offline memory blocks of which some parts > were unplugged, especially, to later offline and remove completely > unplugged memory blocks. The important part is that PageOffline() has > to remain set until the section is offline, so these pages will never > get accessed (e.g., when dumping). The pages