On Sun, 2007-01-07 at 14:20 +0200, Avi Kivity wrote: > > > Well, you did say it was ad-hoc. For reference, this is how I see the > hypercall API: [snip] > - Guest/host communications is by guest physical addressed, as the > virtual->physical translation is much cheaper on the guest (__pa() vs > a page table walk).
Strongly agreed. One of the major problems we had with the PowerPC Xen port was that Xen passes virtual addresses (even userspace virtual addresses!) to the hypervisor. Performing a MMU search on PowerPC is far more convoluted than x86's table walk and is not feasible in software. I'm anxious to avoid the same mistake wherever possible. Of course, even with physical addresses, data structures that straddle page boundaries prevent the hypervisor from mapping contiguous physical pages to discontiguous machine pages (or whatever terminology you want to use). IBM's Power Hypervisor passes hypercall data in registers most of the time. In the places it communicates via memory, I believe the parameter is actually a physical frame number, and the size is explicitly limited to one page. -Hollis ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
