On Fri, 27 Mar 2009 20:06:03 -0400 Rik van Riel <[email protected]> wrote:
> Dave Hansen wrote: > > On Fri, 2009-03-27 at 16:09 +0100, Martin Schwidefsky wrote: > >> If the host picks one of the > >> pages the guest can recreate, the host can throw it away instead of writing > >> it to the paging device. Simple and elegant. > > > > Heh, simple and elegant for the hypervisor. But I'm not sure I'm going > > to call *anything* that requires a new CPU instruction elegant. ;) > > I am convinced that it could be done with a guest-writable > "bitmap", with 2 bits per page. That would make this scheme > useful for KVM, too. This was our initial approach before we came up with the milli-code instruction. The reason we did not use a bitmap was to prevent the guest to change the host state (4 guest states U/S/V/P and 3 host states r/p/z). With the full set of states you'd need 4 bits. And the hosts need to have a "master" copy of the host bits, one the guest cannot change, otherwise you get into trouble. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. _______________________________________________ Virtualization mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/virtualization
