On 30/04/2019 12:32, Christoph Hellwig wrote:
On Tue, Apr 30, 2019 at 12:27:02PM +0100, Robin Murphy wrote:
Hmm, I don't think we need the DMA mask for the MSI mapping, this
should probably always use a 64-bit mask.
If that were true then we wouldn't need DMA masks for regular mappings
either. If we have to map the MSI doorbell at all, then we certainly have to
place it at an IOVA that the relevant device is actually capable of
addressing.
Well, as shown by the patch below we don't even look at the DMA mask
for the MSI page - we just allocate from bottom to top.
In the trivial cookie for unmanaged domains, yes, but in that case the
responsibility is on VFIO to provide a suitable (i.e. sub-32-bit)
address range for that cookie in the first place. In the managed case,
allocation uses the streaming mask via iommu_dma_get_msi_page() calling
__iommu_dma_map(). Admittedly the mask can then get overlooked when
reusing an existing mapping, which strictly could pose a problem if you
have multiple devices with incompatible masks in the same group (and
such that the PCI stuff doesn't already mitigate it), but that's such an
obscure corner case that I'm reticent to introduce the complication to
handle it until it's actually proven necessary.
Robin.
