Re: [Qemu-devel] [RFC ppc-next PATCH 3/6] memory: add memory_region_to_address()

[Alexander Graf]

On 21.03.2013, at 11:53, Peter Maydell wrote:

> On 21 March 2013 08:31, Alexander Graf <address@hidden> wrote:
>> On 14.02.2013, at 07:31, Scott Wood wrote:
>>> This is useful for when a user of the memory region API needs to
>>> communicate the absolute bus address to something outside QEMU
>>> (in particular, KVM).
>>> 
>>> Signed-off-by: Scott Wood <address@hidden>
>> 
>> Peter, how does the VGIC implementation handle this?
> 
> Check kvm_arm_register_device() in target-arm/kvm.c. Basically
> the VGIC device model calls this function to say "tell the kernel
> where this MemoryRegion is in the system address space, when it
> eventually gets mapped". The code in kvm.c uses the memory system's
> Notifier API to get a callback when the region is mapped into
> an address space, which it uses to track the offset in the
> address space. Finally, we use a machine init notifier so that
> just before everything finally starts we can make the KVM ioctls
> to say "here is where everything lives".

Same thing here. The question is how the kvm-vgic code in QEMU finds out where 
it got mapped to. Scott adds this patch to do this, but I'd assume you have 
some other way :)


Alex

> 
> I think this is a pretty neat way of doing it because it means
> neither the interrupt controller device nor the board model
> really need to care about the kernel being told where things
> are mapped; it's all abstracted out into kvm.c. If your
> interrupt controller can be moved around at runtime that's
> probably also handlable, but the ARM code just unregisters its
> notifiers at machine init because the GIC can't move.
> 
> (I think the code assumes the device only gets mapped into
> one address space; this could easily be fixed if it's not true
> at some point in the future.)
> 
> thanks
> -- PMM