On Tue, 2007-07-24 at 08:30 +0300, Avi Kivity wrote: > Rusty Russell wrote: > > On Mon, 2007-07-23 at 13:27 +0300, Avi Kivity wrote: > > > >> Having an address_space (like your patch does) is remarkably simple, and > >> requires few hooks from the current vm. However using existing vmas > >> mapped by the user has many advantages: > >> > >> - compatible with s390 requirements > >> - allows the user to use hugetlbfs pages, which have a performance > >> advantage using ept/npt (but which are unswappable) > >> - allows the user to map a file (which can be regarded as way to specify > >> the swap device) > >> - better ingration with the rest of the vm > >> > > > > You don't need to expose the vmas. You just have userspace point out > > the start+len of each region of memory it wants the guest to be able to > > access, and the address it wants it to appear in the guest. > > > > This is a slight superset of what lguest does in two ways: > > > > 1) my guest address == user address, but I'm looking at adding an offset > > so I don't have to link the launcher binary specially. > > 2) I have only one contiguous region of guest-physical memory, since I > > can place device memory immediately above "normal" mem. > > > > > > My intent was to allow userspace to establish assign a virtual address > range into a memory slot. > > So long as you don't do swapping, all is simple, since you can do a > get_user_pages() on initialization or when installing a shadow pte. But > if you want to swap, you need: > > - a way to transfer the dirty bit from the shadow ptes to the struct page
Actually, get_user_pages() does that for you. You have to make R/O any writable pte where the guest doesn't set the dirty bit (so you can trap it later) but last I put a printk in there, Linux doesn't do that. > - a way to let the vm rmap know that there are shadow ptes that point to > the page in addition to Linux ptes. These shadow ptes may be in a > different format than Linux ptes. > - a different tlb invalidation method with ASIDs Well first I was just going to see how well hooking into the shrinker works. That might be sufficient: just throw out shadow refs to pages when there's pressure. If not, it does get harder. A callback in the mm struct to say "I want to swap your page out" is required if we don't take a reference to the page. Dirty bit handling would be an interesting issue (maybe the callback can say "No!" and dirty the page again?). I fear mm code. > It's not going to be simple. Yeah, but it's one thing stopping lguest from being non-root usable, so I want it there, too. Cheers, Rusty. ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
