[PATCH] ARM: KVM: Allow host virtual timer irq number to be different from guest virtual timer irq number

[Peter Maydell]

On 25 April 2013 19:04, Christoffer Dall <cdall at cs.columbia.edu> wrote:
> I prefer not hard-coding this stuff in the kernel, but let user space
> decide this. If we have good technical arguments not to do that (such
> as knowing that this is always defined per-core and not for an SoC
> (ARM guys?) then at least the patch should lookup the target processor
> and set the irq number accordingly.

Well, this is all implementation-defined. The ARM ARM mandates
that the generic timers deliver a PPI, and that it must be the
same PPI for all processors in an MP implementation, but not which
PPI. The A15 and A7 happen to both be hardwired to ID27. You could
in theory design a core which let the SoC configure the virtual
timer ID (or let the guest arbitrarily program it, for that
matter, I suppose), though I'm not sure why you'd want to.

I think I'd take the simple approach of saying "the timer PPI
is a fixed property of the guest CPU" unless somebody actually
builds something where it isn't fixed... (for that CPU we
could then define it as a feature argument to KVM_ARM_VCPU_INIT).

thanks
-- PMM