On 1/11/21 11:28 AM, BALATON Zoltan wrote: > On Mon, 11 Jan 2021, Jiaxun Yang wrote: >> On Mon, Jan 11, 2021, at 3:25 AM, BALATON Zoltan wrote: >>> On Sun, 10 Jan 2021, Philippe Mathieu-Daudé wrote: >>>> +PCI experts >>>> >>>> On 1/10/21 1:43 AM, BALATON Zoltan wrote: >>>>> On Sun, 10 Jan 2021, Philippe Mathieu-Daudé wrote: >> >> [...] >> >>>> I'm not a PCI expert but my understanding is PCI device functions are >>>> restricted to the PCI bus address space. The host bridge may map this >>>> space within the host. >>>> >>>> QEMU might be using get_system_memory() because for some host bridge >>>> the mapping is not implemented so it was easier this way? >>> >>> Maybe, also one less indirection which if not really needed is a good >>> thing for performance so unless it's found to be needed to use another >>> address space here I'm happy with this as it matches what other similar >>> devices do and it seems to work. Maybe a separate address space is only >>> really needed if we have an iommu? >> >> Hi Zoltan, >> >> It is possible for bonito to remap PCI address space so maybe it's >> essential for bonito. > > I'm still not sure it's needed or how that would work. Maybe while it's > possible to remap these, all guests just map these one-to-one (otherwise > they may need to do some address translation which is much better > avoided) so in practice we don't need to emulate this. If we use a > different memory region maybe we also need some additional iommu code > somewhere to connect the two but I'm not sure, I haven't tried since > most other isa bridges do the same way using system_memory and this > seems to work. I'm also a bit concerned about additional overhead which > we could avoid if possible. Just to model something that's not really > used I don't think it's worth the additional complexity and possible > performance loss unless it's found to be needed to get some guests work.
Fine. Reviewed-by: Philippe Mathieu-Daudé <f4...@amsat.org>
