On Tue, Jan 17, 2017 at 12:09 PM, Marc Zyngier <marc.zyng...@arm.com> wrote: > On 26/12/16 17:11, Jintack Lim wrote: >> The ARM architecture defines the EL1 physical timer and the virtual >> timer, and it is reasonable for an OS to expect to be able to access >> both. However, the current KVM implementation does not provide the EL1 >> physical timer to VMs but terminates VMs on access to the timer. >> >> On VHE systems, this would be as simple as allowing full access to the >> EL1 physical timer to VMs because the KVM host does not use the EL1 >> physical timer. However, on non-VHE systems, the KVM host already uses >> the EL1 physical timer which prevents us from granting full access of >> the EL1 physical timer to VMs. >> >> This patchset enables VMs to use the EL1 physical timer through >> trap-and-emulate. The KVM host emulates each EL1 physical timer >> register access and sets up the background timer accordingly. When the >> background timer expires, the KVM host injects EL1 physical timer >> interrupts to the VM. Alternatively, it's also possible to allow VMs to >> access the EL1 physical timer without trapping. However, this requires >> somehow using the EL2 physical timer for the Linux host while running >> the VM instead of the EL1 physical timer. Right now I just implemented >> trap-and-emulate because this was straightforward to do, and I leave it >> to future work to determine if transferring the EL1 physical timer state >> to the EL2 timer provides any performance benefit. >> >> This feature will be useful for any OS that wishes to access the EL1 >> physical timer. Nested virtualization is one of those use cases. A >> nested hypervisor running inside a VM would think it has full access to >> the hardware and naturally tries to use the EL1 physical timer as Linux >> would do. Other nested hypervisors may try to use the EL2 physical timer >> as Xen would do, but supporting the EL2 physical timer to the VM is out >> of scope of this patchset. This patchset will make it easy to add the >> EL2 timer support in the future, though. >> >> Note, Linux VMs booting in EL1 will be unaffected by this patch set and >> will continue to use only the virtual timer and this patch set will >> therefore not introduce any performance degredation as a result of >> trap-and-emulate. > > Hi Jintack, > > Any chance you could address Christoffer's comments and respin this > series? This looks like a good enhancement to our emulation, and > definitely a requirement for the nested work, so I'm obviously keen on it.
Hi Marc, Yes, I plan to respin this patch series this week. Thanks, Jintack > > Thanks, > > M. > -- > Jazz is not dead. It just smells funny... > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
