On Wed, 26 Feb 2014 14:25:53 -0800, Christoffer Dall christoffer.dall@linaro.org wrote:
On Wed, Feb 26, 2014 at 09:48:43PM +0000, Leif Lindholm wrote:
On Wed, Feb 26, 2014 at 08:55:58PM +0100, Arnd Bergmann wrote:
On Wednesday 26 February 2014 10:34:54 Christoffer Dall wrote:
ARM VM System Specification
Goal
The goal of this spec is to allow suitably-built OS images to run on all ARM virtualization solutions, such as KVM or Xen.
Recommendations in this spec are valid for aarch32 and aarch64 alike, and they aim to be hypervisor agnostic.
Note that simply adhering to the SBSA [2] is not a valid approach, for example because the SBSA mandates EL2, which will not be available for VMs. Further, the SBSA mandates peripherals like the pl011, which may be controversial for some ARM VM implementations to support. This spec also covers the aarch32 execution mode, not covered in the SBSA.
I would prefer if we can stay as close as possible to SBSA for individual hardware components, and only stray from it when there is a strong reason. pl011-subset doesn't sound like a significant problem to implement, especially as SBSA makes the DMA part of that optional. Can you elaborate on what hypervisor would have a problem with that?
I believe it comes down to how much extra overhead pl011-access-trap would be over virtio-console. If low, then sure. (Since there are certain things we cannot provide SBSA-compliant in the guest anyway, I wouldn't consider lack of pl011 to be a big issue.)
I don't think it's about overhead, sure pl011 may be slower, but it's a serial port, does anyone care about performance of a console? pl011 should be good enough for sure.
The reason pl011 is specified in the SBSA is to have a reliable output port available from the first instruction. It is a debug feature. Hardware vendors aren't even need to wire it up to a physical serial port. It is just as valid to wire it to the RAS controller.
g.