On Thu, 2015-10-29 at 11:31 -0700, Andy Lutomirski wrote: > On Oct 28, 2015 6:11 PM, "Benjamin Herrenschmidt" > <benh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > On Thu, 2015-10-29 at 09:42 +0900, David Woodhouse wrote: > > > On Thu, 2015-10-29 at 09:32 +0900, Benjamin Herrenschmidt wrote: > > > > > > > On Power, I generally have 2 IOMMU windows for a device, one at > > > > the > > > > bottom is remapped, and is generally used for 32-bit devices > > > > and the > > > > one at the top us setup as a bypass > > > > > > So in the normal case of decent 64-bit devices (and not in a VM), > > > they'll *already* be using the bypass region and have full access > > > to > > > all of memory, all of the time? And you have no protection > > > against > > > driver and firmware bugs causing stray DMA? > > > > Correct, we chose to do that for performance reasons. > > Could this be mitigated using pools? I don't know if the net code > would play along easily. Possibly, the pools we have already limit the lock contention but we still have the map/unmap overhead which under a hypervisor can be quite high. I'm not necessarily against changing the way we do things but it would have to be backed up with numbers. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
