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Re: [Xen-devel] [PATCH v4] hw/passthrough: Prevent QEMU from mapping PCI option ROM at address 0

>>> On 12.05.14 at 17:59, <malcolm.crossley@xxxxxxxxxx> wrote:
> On 12/05/14 16:52, Jan Beulich wrote:
>>>>> On 12.05.14 at 17:36, <malcolm.crossley@xxxxxxxxxx> wrote:
>>> The PCI option ROM BAR uses the LSB to indicate if the BAR is enabled.
>>> The AMD graphics driver sets the address bit's of the BAR to 0 but leaves 
>>> the
>>> LSB set to 1. Whilst this is not good practice, QEMU should be ignoring the
>>> non address parts of the BAR.
>> All you say above only warrants the PCI defined bits to be masked
>> off, ...
> But we've only got 4k mapping granularity with the IOMMU, so if we try
> to map to an address between 2k and 4k then we will overlap with the
> bottom 2k which is likely to cause problems.

What has the IOMMU got to do with this? Any such overlap would
be similarly (non-)problematic elsewhere in the address space.


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