Avi, On Thu, May 31, 2007 at 11:39:04AM +0300, Avi Kivity wrote: > Stephane Eranian wrote: > >Hello, > > > >Looking at kvm-26, it seems that the CPUID values as seen by the guest OS > >are still hardcoded for i386/x86-64 at least. > > > >For performance counter virtualization, the guest needs to see the *actual* > >family/model information in order to correctly program the counters. > > > >It would be fairly simple to grab that information from /proc/cpuinfo > >at init time in qemu. > > > >However, I am wondering if there would be side effects of using the > >actual CPUID which could cause troubles to KVM or the guest. > > > > > > The main issue is migration (and save/restore). If you migrate to a > host with fewer capabilities, applications may fail when they use > unavailable instructions that they successfully detected earlier. > In the case of heterogeneous migration, clearly performance counters will not work well, especially for unmodified guests. But I can also see problems when migrating from Intel Core to older P4 for instance.
> I think the best solution is to default to the host's capabilities, but > allow command line switches to override them. This way a management > application in a server farm can set a site-wide least common > denominator, while a home user can enjoy the latest and greatest > instructions on their machine. > I agree. > Upstream qemu already has a -cpu (or similar) switch for non-x86; we can > probably use that. > Probably, but in my particular case, you'd have to be able to specify vendor/family/model. > (there's another possible issue - some future features may require > support from the hypervisor - that may conflict with defaulting to to > the host feature set. maybe kvm should mask out any unknown features) > The question is how do you identify unknown features which do require KVM support? -- -Stephane ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kvm-devel
