On Tue, Apr 2, 2013 at 5:50 PM, Scott Wood <scottwood@xxxxxxxxxxxxx> wrote: > On 04/02/2013 04:38:45 PM, Alex Williamson wrote: >> >> On Tue, 2013-04-02 at 16:08 -0500, Stuart Yoder wrote: >> > On Tue, Apr 2, 2013 at 3:57 PM, Scott Wood <scottwood@xxxxxxxxxxxxx> >> > wrote: >> > >> > C. Explicit mapping using normal DMA map. The last idea is >> > >> > that >> > >> > we would introduce a new ioctl to give user-space an fd to >> > >> > the MSI bank, which could be mmapped. The flow would be >> > >> > something like this: >> > >> > -for each group user space calls new ioctl >> > >> > VFIO_GROUP_GET_MSI_FD >> > >> > -user space mmaps the fd, getting a vaddr >> > >> > -user space does a normal DMA map for desired iova >> > >> > This approach makes everything explicit, but adds a new >> > >> > ioctl >> > >> > applicable most likely only to the PAMU (type2 iommu). >> > >> >> > >> And the DMA_MAP of that mmap then allows userspace to select the >> > >> window >> > >> used? This one seems like a lot of overhead, adding a new ioctl, new >> > >> fd, mmap, special mapping path, etc. >> > > >> > > >> > > There's going to be special stuff no matter what. This would keep it >> > > separated from the IOMMU map code. >> > > >> > > I'm not sure what you mean by "overhead" here... the runtime overhead >> > > of >> > > setting things up is not particularly relevant as long as it's >> > > reasonable. >> > > If you mean development and maintenance effort, keeping things well >> > > separated should help. >> > >> > We don't need to change DMA_MAP. If we can simply add a new "type 2" >> > ioctl that allows user space to set which windows are MSIs, it seems >> > vastly >> > less complex than an ioctl to supply a new fd, mmap of it, etc. >> > >> > So maybe 2 ioctls: >> > VFIO_IOMMU_GET_MSI_COUNT > > > Do you mean a count of actual MSIs or a count of MSI banks used by the whole > VFIO group? I meant # of MSI banks, so VFIO_IOMMU_GET_MSI_BANK_COUNT would be better. >> > VFIO_IOMMU_MAP_MSI(iova, size) > > > Not sure how you mean "size" to be used -- for MPIC it would be 4K per bank, > and you can only map one bank at a time (which bank you're mapping should be > a parameter, if only so that the kernel doesn't have to keep iteration state > for you). The intent was for user space to tell the kernel which windows to use for MSI. So I envisioned a total size of window-size * msi-bank-count. Stuart -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
