Re: [RFC PATCH 22/30] iommu: Bind/unbind tasks to/from devices

[Joerg Roedel <joro@8bytes.org>]

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