On Fri, Mar 03, 2017 at 06:39:58PM +0000, Jean-Philippe Brucker wrote: > Yes, it would be nice to have a common PASID allocator. But I don't > think that a system-wide PASID space is workable for us. At the moment > systems might have a few identical devices all supporting 20 bits of > PASID. But consider the case where one odd device can only handle four > address spaces, and supports a maximum of two PASID bits. We'd quickly > run out of PASIDs to hand to such devices, even though we could easily > have one PASID space per endpoint (from a quick glance at the specs, I > assume that both Intel and AMD IOMMUs offer one PASID table per RID.) But that shouldn't be a problem if we allocate PASIDs top-down (meaning starting from the biggest value supported by a given device), right? Then we can satisfy the devices with 16 or 20 bit PASIDs and still have the 2-bit PASIDs free for the devices that need it. Joerg
