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Date: Thu, 29 Dec 2011 18:16:59 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/3] Add a new PCI region type to supports
 64 bit ranges
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To: Alexey Korolev <alexey.korolev@endace.com>
Cc: sfd@endace.com, yamahata@valinux.co.jp, Kevin O'Connor <kevin@koconnor.net>, seabios@seabios.org, qemu-devel@nongnu.org

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.