Re: [libvirt] [Qemu-devel] Modern CPU models cannot be used with libvirt

On Sun, Mar 11, 2012 at 10:33:15AM -0500, Anthony Liguori wrote: > On 03/11/2012 09:56 AM, Gleb Natapov wrote: >> On Sun, Mar 11, 2012 at 09:12:58AM -0500, Anthony Liguori wrote: >>> -cpu best wouldn't solve this. You need a read/write configuration >>> file where QEMU probes the available CPU and records it to be used >>> for the lifetime of the VM. >> That what I thought too, but this shouldn't be the case (Avi's idea). >> We need two things: 1) CPU model config should be per machine type. >> 2) QEMU should refuse to start if it cannot create cpu exactly as >> specified by model config. > > This would either mean: > > A. pc-1.1 uses -cpu best with a fixed mask for 1.1 > > B. pc-1.1 hardcodes Westmere or some other family > This would mean neither A nor B. May be it wasn't clear but I didn't talk about -cpu best above. I am talking about any CPU model with fixed meaning (not host or best which are host cpu dependant). Lets take Nehalem for example (just to move from Westmere :)). Currently it has level=2. Eduardo wants to fix it to be 11, but old guests, installed with -cpu Nehalem, should see the same CPU exactly. How do you do it? Have different Nehalem definition for pc-1.0 (which level=2) and pc-1.1 (with level=11). Lets get back to Westmere. It actually has level=11, but that's only expose another problem. Kernel 3.3 and qemu-1.1 combo will support architectural PMU which is exposed in cpuid leaf 10. We do not want guests installed with -cpu Westmere and qemu-1.0 to see architectural PMU after upgrade. How do you do it? Have different Westmere definitions for pc-1.0 (does not report PMU) and pc-1.1 (reports PMU). What happens if you'll try to run qemu-1.1 -cpu Westmere on Kernel < 3.3 (without PMU support)? Qemu will fail to start.