On Wed, Mar 2, 2016 at 4:45 PM, Joerg Roedel <j...@8bytes.org> wrote: > On Wed, Mar 02, 2016 at 03:58:18PM +0300, David Kiarie wrote: >> On Wed, Mar 2, 2016 at 3:35 PM, Joerg Roedel <j...@8bytes.org> wrote: >> > On Wed, Mar 02, 2016 at 11:40:04AM +0300, David Kiarie wrote: >> >> What effect is setting the value next_bit to last invalidated index >> >> supposed to have ? >> > >> > The idea is to safe the IOTLB flush by not re-using the address-range >> > until the allocator wraps around to 0 again. We only allocate address >> > ranges between next_bit and end-of-range. This way we don't need a flush >> > after every unmap operation. >> >> Okay, I'll look at this issue again. >> >> Last unrelated question. If I have 'iommu=pt' IOMMU doesn't seem to >> allocate any addresses and doesn't populate the 'root page table' >> until I try to pass-through a device. Why is that set like this ? > > The pt stands for passthrough. In this mode the IOMMU is enabled, but > configured in way as if it is disabled. This means that all devices get > access to the physical address space and no remapping through the > DMA-API is done at all. Often this is used for performance reasons. > > This only changes when a device is is assigned to a guest. In that case > it will only see the guest-physical address space via a page-table.
Thanks for the insight! > > > Joerg > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
