Re: [Qemu-devel] [PATCH 04/16] exec.c: Add address space index to CPUIOTLBEntry

[Edgar E. Iglesias]

On Fri, Nov 06, 2015 at 01:45:29PM +0000, Peter Maydell wrote:
> On 6 November 2015 at 13:34, Edgar E. Iglesias <address@hidden> wrote:
> > On Thu, Nov 05, 2015 at 06:15:46PM +0000, Peter Maydell wrote:
> >> Add the address space index to CPUIOTLBEntry, and use this to pass it
> >> to iotlb_to_region(), so that we use the correct AddressSpace when
> >> doing IO path lookups.
> >
> > Hi Peter,
> >
> > I think this works but eventually when we add support for CPUs behind
> > IOMMUs I think things will be easier if we store a pointer to the
> > AS instead of an index in the IOTLB. address_space_translate_for_iotlb()
> > with IOMMU support may be implemented so that it returns a different
> > address space as it walks tha memory hierarchy and translate things.
> >
> > Do you see any issues with storing pointers to the AS instead of an
> > index?
> 
> Yeah, we can't deal with arbitrary AddressSpaces here. We need a
> CPUAddressSpace, because we use the cached RCU-protected memory_dispatch
> pointer. Once you know that you have to be dealing with one of the fixed
> CPUAddressSpaces, then you might as well just keep the index rather than
> an arbitrary pointer.

OK, I think we'll have to have another look once we do the IOMMU stuff. My
view has probably been to simplistic.

Best regards,
Edgar