On Wed, Sep 14, 2016 at 02:00:29PM +1000, David Gibson wrote: [...]
> > > > > > > > > > > So > > > > > > IIUC this is a question about "naming" but not the > > > > > > implementations... > > > > > > I suppose it is really a matter of taste, and both work for me > > > > > > (either > > > > > > INVALIDATION/CHANGE or UNMAP/MAP). > > > > > > > > > > No.. it is a question of implementation. My point is that I don't > > > > > think the new permission is sufficient information to let you know if > > > > > a notification is necessary. You need to know if there was an > > > > > existing mapping at that IOBA. > > > > > > > > My understanding is that we don't need to know that. Because IIUC > > > > there are only map_page() and unmap_page() in guest IOMMU driver > > > > (please check dma_map_ops in kernel). There is no chance for anyone to > > > > "change" the content of the mapping, unless it calls unmap_page() then > > > > with a map_page(). In that case, we'll have two IOTLB invalidation > > > > requests. > > > > > > That's assuming a Linux guest using the current guest IOMMU model. > > > > > > I don't think we do so in practice, but the PAPR hypercall interface > > > allows in-place changing of a mapping. The interface is just "set > > > this IOPTE to this value". > > > > I see. Even if so, QEMU IOMMU emulation codes can convert one CHANGE > > request into UNMAP and a continuous MAP, right? > > Yes, I guess so. Why is that preferable to issuing a single > notification to both "map" and "unmap" listeners though? So I think we should be talking about the same thing here (please correct me if I am wrong...). Please review v4 of this series and see whether that works (I renamed CHANGE into MAP, so there will be MAP/UNMAP, and I think things are clearer with it). Thanks! -- peterx
