On 14.08.2013, at 10:11, Marc Zyngier wrote: > On 2013-08-14 07:32, Alexander Graf wrote: >> On 13.08.2013, at 20:03, Peter Maydell wrote: >> >>> These patches add support to target-arm for '-cpu host'. >>> The general semantics are the same as for ppc and x86 (ie "whatever >>> the host kernel can support that looks basically like the host >>> CPU"), but the mechanism is a little different. >>> >>> The kernel API (currently still proposed rather than implemented, >>> hence the RFC nature of this patchset) is that the existing >>> KVM_ARM_VCPU_INIT supports a new 'target' value KVM_ARM_TARGET_HOST, >>> which it treats as "whatever you are". On the userspace side, >>> we use this if the kernel supports it. If it doesn't then we >>> know the kernel must be an A15-on-A15 only one, and so can >>> safely implement '-cpu host' with KVM_ARM_TARGET_CORTEX_A15. >> >> How do you know what core specific registers QEMU can expect from >> this particular CPU? Imagine ARM changes the MMU implementation in the >> next ARMv8 CPU. With -cpu host you wouldn't be able to support gdbstub >> anymore, because you wouldn't know whether the MMU format is the old >> or the new one. > > Well, we're already there. A15 supports both classic page tables and LPAE. > > You can discover which one is being used by inspecting the guest, and I'd > fully expect future versions of the architecture to expose bits in the ID > registers indicating the various supported extensions. Can you fetch those from user space? If so, we should probably create a "host" CPU type class on the fly from the host's ID registers that adjusts itself to the correct callbacks. Alex _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/cucslists/listinfo/kvmarm
