Re: [RFC] Handling CP15 timer without in-kernel irqchip

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/10/2015 12:16, Peter Maydell wrote:
> On 2 October 2015 at 11:05, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> On 02/10/2015 11:58, Peter Maydell wrote:
>>> I definitely dislike the latter -- userspace ends up having to
>>> emulate part of the CPU even though that CPU support is really
>>> there in hardware. Also it requires us to edit the device tree,
>>> which means it won't work at all on boards other than 'virt'
>>> where we use the kernel's device tree rather than creating our
>>> own. Better for the kernel to forward the timer
>>> interrupts back out to userspace's irq controller.
>>
>> How do boards other than 'virt' work when emulated without KVM?  It must
>> be possible to emulate the physical timer in QEMU.
> 
> Without KVM is easy -- we emulate the physical timer as just
> one of the parts of the emulated CPU. With KVM, we don't emulate
> the CPU at all. We don't try to handle a "half TCG half KVM" setup.

I mean in the device tree.  Does the boot loader realize it's under a
hypervisor, and provide different device trees to the kernel?

Paolo