Re: [Qemu-devel] [PATCH 2/3] Add a new PCI region type to supports 64 bit ranges

[Michael S. Tsirkin]

On Thu, Dec 29, 2011 at 06:32:37PM +1300, Alexey Korolev wrote:
> 
> >>@@ -69,6 +72,8 @@ static enum pci_region_type pci_addr_to_type(u32 addr)
> >>  {
> >>      if (addr&  PCI_BASE_ADDRESS_SPACE_IO)
> >>          return PCI_REGION_TYPE_IO;
> >>+    if (addr&  PCI_BASE_ADDRESS_MEM_TYPE_64)
> >>+        return PCI_REGION_TYPE_PREFMEM_64;
> >This seems dangerous - a 64bit bar can be non-prefetchable - getting
> >this wrong could cause random (hard to debug) crashes.
> >
> Just out of curiosity - how this could happen? Having 64bit
> non-prefetchable BAR implies that the device is not behind
> any bridge (as bridges describe 64bit ranges for prefetchable
> memory only). Is it possible on nowadays systems?

Yes. qemu puts all devices directly on the root bus.
system devices are also commonly located on the root bus.