On 25/06/2015 19:08, Andreas Färber wrote: > > I said "I think this patch is incorrect, because you do not install a > > separate address space for each CPU. Also, the CPU address space is > > only used with TCG so it should be guarded by "if (tcg_enabled())"." > > > > By the way, now TCG _is_ installing a separate address space per CPU > > already, so the patch can simply guard the code with "if (tcg_enabled())". > > Is the APIC MemoryRegion not used by KVM?
It's used if the userspace LAPIC is. It's not used together with the kernel LAPIC (accesses really are trapped by the kernel). > Otherwise if we still need the > ugly code path for KVM, that's not much of an improvement here. > > And is installing a separate address space per CPU for KVM difficult due > to kernel limitations, or is this just a few lines of QEMU code that Zhu > or someone would need to write? :) It's basically impossible. Even though support for multiple address spaces is going to be in Linux 4.2, there are going to be just two: SMM and not SMM. You don't really want to do O(#cpus) stuff in KVM, where the number of CPUs can be 200 or more. TCG is okay because the #cpus is not really going to be more than 4-ish. Paolo
