On Wed, Mar 12, 2025 at 05:07:25PM +0000, Nikita Kalyazin wrote: > However if MISSING is not registered, the kernel will auto-populate with a > clear page, ie there is no way to inject custom content from userspace. To > explain my use case a bit more, the population thread will be trying to copy > all guest memory proactively, but there will inevitably be cases where a > page is accessed through pgtables _before_ it gets populated. It is not > desirable for such access to result in a clear page provided by the kernel. IMHO populating with a zero page in the page cache is fine. It needs to make sure all accesses will go via the pgtable, as discussed below in my previous email [1], then nobody will be able to see the zero page, not until someone updates the content then follow up with a CONTINUE to install the pgtable entry. If there is any way that the page can be accessed without the pgtable installation, minor faults won't work indeed. > > > as long as the content can only be accessed from the pgtable (either via > > mmap() or GUP on top of it), then afaiu it could work similarly like > > MISSING faults, because anything trying to access it will be trapped. [1] -- Peter Xu
