On Wed, Apr 24, 2019 at 12:33:11PM -0700, Matthew Garrett wrote: > On Wed, Apr 24, 2019 at 12:28 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > But you can't have a new PageFlag. Can you instead zero the memory in > > unmap_single_vma() where we call uprobe_munmap() and untrack_pfn() today? > > Is there any way the page could be referenced by something other than > a VMA at this point? If so we probably don't want to zero it here, but > we do want to zero it when the page is finally released (which is why > I went with a page flag) It could be the target/source of direct I/O, or userspace could have registered it with an RDMA device, or ... It depends on the semantics you want. There's no legacy code to worry about here. I was seeing this as the equivalent of an atexit() handler; userspace is saying "When this page is unmapped, zero it". So it doesn't matter that somebody else might be able to reference it -- userspace could have zeroed it themselves.
