2015-03-16 11:16-0500, Joel Schopp: > On 03/12/2015 04:20 PM, Radim Krčmář wrote: > > 2015-03-12 15:17-0500, Joel Schopp: > >> There isn't really a valid reason for kvm to intercept cr* reads > >> on svm hardware. The current kvm code just ends up returning > >> the register > > There is no need to intercept CR* if the value that the guest should see > > is equal to what we set there, but that is not always the case: > > - CR0 might differ from what the guest should see because of lazy fpu > Based on our previous conversations I understand why we have to trap the > write to the CR0 ts bit for lazy fpu, but don't understand why that > should affect a read. KVM keeps one CR0 with guest's state (svm.vcpu.arch.cr0) and a second one that is loaded to hardware CR0 on VMRUN (svm.vmcb->save.cr0); these two might not match. If we didn't intercept read, it would return hardware CR0, so the guest could do CLTS (change svm.vcpu.arch.cr0) and read CR0.TS = 1, because of lazy FPU. Correct emulation is what we want. > > CR2 and CR8 already aren't intercepted, so it looks like only CR0 and > > CR4 could use some optimizations. > I'll send out a v2 with these less aggressive optimizations. Thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
