On Fri, 27 Mar 2009 20:06:03 -0400
Rik van Riel <riel@xxxxxxxxxx> wrote:
Dave Hansen wrote:On Fri, 2009-03-27 at 16:09 +0100, Martin Schwidefsky wrote:I am convinced that it could be done with a guest-writableIf the host picks one of theHeh, simple and elegant for the hypervisor. But I'm not sure I'm going
pages the guest can recreate, the host can throw it away instead of writing
it to the paging device. Simple and elegant.
to call *anything* that requires a new CPU instruction elegant. ;)
"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.