On 06.07.22 10:20, Chao Peng wrote: > This patch introduces memfile_notifier facility so existing memory file > subsystems (e.g. tmpfs/hugetlbfs) can provide memory pages to allow a > third kernel component to make use of memory bookmarked in the memory > file and gets notified when the pages in the memory file become > invalidated. Stupid question, but why is this called "memfile_notifier" and not "memfd_notifier". We're only dealing with memfd's after all ... which are anonymous files essentially. Or what am I missing? Are there any other plans for fs than plain memfd support that I am not aware of? > > It will be used for KVM to use a file descriptor as the guest memory > backing store and KVM will use this memfile_notifier interface to > interact with memory file subsystems. In the future there might be other > consumers (e.g. VFIO with encrypted device memory). > > It consists below components: > - memfile_backing_store: Each supported memory file subsystem can be > implemented as a memory backing store which bookmarks memory and > provides callbacks for other kernel systems (memfile_notifier > consumers) to interact with. > - memfile_notifier: memfile_notifier consumers defines callbacks and > associate them to a file using memfile_register_notifier(). > - memfile_node: A memfile_node is associated with the file (inode) from > the backing store and includes feature flags and a list of registered > memfile_notifier for notifying. > > In KVM usages, userspace is in charge of guest memory lifecycle: it first > allocates pages in memory backing store and then passes the fd to KVM and > lets KVM register memory slot to memory backing store via > memfile_register_notifier. Can we add documentation/description in any form how the different functions exposed in linux/memfile_notifier.h are supposed to be used? Staring at memfile_node_set_flags() and memfile_notifier_invalidate() it's not immediately clear to me who's supposed to call that and under which conditions. -- Thanks, David / dhildenb
