This email is just a quick summary of what we (Linaro) are planning in the way of QEMU work to support KVM on ARM Cortex-A15. The idea is to let people know what's coming up, find out if we've forgotten anything, and avoid people duplicating work unnecessarily. Most of this is based on a useful session at the recent 'ARM server mini-summit' in Orlando (UDS/Linaro Connect) at the beginning of this month.
The work we're currently proposing to do falls into three parts:
* refactor QEMU's cp15 register handling
At the moment QEMU handles cp15 accesses by calling out to a single helper function which is an enormous set of nested switch statements to handle the different coprocessor registers. Access permissions are checked separately at translate time. This design makes specifying board-dependent or cpu-dependent registers somewhat painful; it's also easy for the access permission checks to be out of sync. There is no support for banked cp15 registers either (needed for trustzone and virtualisation). We need a better design which lets a board or core register handler routines for cp15 registers. This will make the code cleaner and more maintainable as a base for new features.
This isn't strictly a requirement for KVM, but we're going to want KVM to be able to hand off cp15 accesses to QEMU, and I don't think that's going to be maintainable or reliable without this refactoring.
(https://blueprints.launchpad.net/qemu-linaro/+spec/cp15-rework)
* A15 system model
Basically a QEMU model of a Versatile-Express with a Cortex-A15 minus the virtualization and LPAE extensions. This needs the A15 private peripherals (just the GIC in the right place in the memory map, really; generic timer not required) and the new memory map version of the vexpress board model, plus some new cp15 registers. (Bill Carson has already done some patches in this area but they need a little rework and may have minor missing pieces.)
https://blueprints.launchpad.net/qemu-linaro/+spec/initial-a15-system-model
* miscellaneous integration work
We're aiming for a reasonable working prototype of A15 guest on an A15 Fast Model host here; we need to fix at least some of the bugs which currently mean upstream QEMU doesn't work on ARM hosts, sort out which kernel and qemu trees we are developing from, and get things running in our validation lab's continuous integration setup.
https://blueprints.launchpad.net/qemu-linaro/+spec/qemu-kvm-getting-started
Also on the radar is a fourth piece of work:
* QEMU virtio-mmio support
This is adding support for the 'mmio' virtio transport, which will allow virtio support in a versatile-express model. We're going to need this at some point but the current thought is that we want to do the above listed more important bits of work first... (The exception would probably be if it turned out that this was sufficiently useful for making early KVM development easier)
https://blueprints.launchpad.net/qemu-linaro/+spec/add-amba-virtio-support
So, questions: (1) did we forget something important? (2) is anybody else already planning to do any of this (or would like to start)? if so we should coordinate... (3) is there anything that the kernel folk need/want earlier rather than later?
thanks -- PMM