Re: [Qemu-devel] [PATCH] pci: add standard bridge device

[Avi Kivity]

On 08/22/2011 06:13 AM, Wen Congyang wrote:
> At 08/19/2011 11:26 PM, Avi Kivity Write:
> >  On 08/18/2011 10:12 PM, Wen Congyang wrote:
> >>  >>
> >>  >>   The following patch can fix this problem, but I'm not sure whether it
> >>  >>   is right.
> >>  >
> >>  >   It's correct but insufficient, the filtering code (pci_bridge_filter)
> >>  >   needs to be updated to use the memory API.
> >>
> >>  I read the function pci_bridge_filter(), and the function only read
> >>  PCI bridge's config space(command, base and limit). If base>   limit,
> >>  it will set addr to PCI_BAR_UNMAPPED.
> >>
> >>  I do not find anything that needs to updated to use the memory API.
> >
> >  Currently it doesn't do any filtering at all.  Bridges need to create a
> >  new address space, then attach aliases of this region (corresponding to
> >  the filtered area and to the legacy vga space) to the parent bus'
> >  address space.
>
> Hmm, does this problem exist before memory API is introduced?

Yes.  There was code to handle it, but I don't think it was correct.

> >
> >>  I add a scsi controller on pci bus1, and a scsi disk on this controller.
> >>  I can read and write this disk, and I do not meet any problem.
> >>
> >
> >  However, filtering doesn't work.  You could put a BAR outside the
> >  filtered area and it would be visible to the guest.
>
> How to put a BAR outside the filtered area and confirm whether it would be
> virible to the guest?


You could use something like kvm-unit-tests.git to write a simple test 
that sets up a BAR (say from hw/ivshmem.c), writes and reads to see that 
it is visible, programs the bridge to filter part of the BAR out, then 
writes and reads again to verify that the correct part is filtered out.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.