Re: [Qemu-devel] [PATCH] pci: implement bridge filtering

[Avi Kivity <avi@redhat.com>]

On 09/20/2011 11:09 AM, Wen Congyang wrote:
> At 09/14/2011 09:48 AM, Wen Congyang Write:
> >  At 09/05/2011 02:13 AM, Michael S. Tsirkin Write:
> >>  Support bridge filtering on top of the memory
> >>  API as suggested by Avi Kivity:
> >>
> >>  Create a memory region for the bridge's address space.  This region is
> >>  not directly added to system_memory or its descendants.  Devices under
> >>  the bridge see this region as its pci_address_space().  The region is
> >>  as large as the entire address space - it does not take into account
> >>  any windows.
> >>
> >>  For each of the three windows (pref, non-pref, vga), create an alias
> >>  with the appropriate start and size.  Map the alias into the bridge's
> >>  parent's pci_address_space(), as subregions.
> >>
> >>  Signed-off-by: Michael S. Tsirkin<mst@redhat.com>
> >>  ---
> >>
> >>  The below seems to work fine for me so I applied this.
> >>  Still need to test bridge filtering, any help with this
> >>  appreciated.
> >>
> >
> >
> >  I test bridge filtering, and the BAR still can be visible on guest even if
> >  I change the memory region.
>
> Hi Michael S. Tsirkin:
> I test pci bridge filtering on real hardware, and I find that I can mmap
> the resource after I change the memory base and memory limit(The BAR should
> be not visible on OS after changing the memory region).
>
> So I try to write and read to the BAR. Here is my test result:
> 1. Before changing the pci bridge's memory region, I can read and write to the memory, and
>     I can get the same value that I write.
>
> 2. After changing the pci bridge's memory region, I can still read and write to the memory,
>     but it is very slow, and I can not get the same value that I write(The value is always 0).
>
> Does this result means that pci bridge filtering works fine?
>

Yes.  Instead of hitting the BAR, you hit the default mmio handler.

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