On Thu, Mar 04, 2021 at 09:46:03AM -0800, Jacob Pan wrote:

Hi Jean-Philippe,

On Thu, 4 Mar 2021 10:49:37 +0100, Jean-Philippe Brucker
[off-list ref] wrote:

quoted

On Wed, Mar 03, 2021 at 04:02:05PM -0800, Jacob Pan wrote:

quoted

Hi Jacob,

On Wed, 3 Mar 2021 13:17:26 -0800, Jacob Pan
[off-list ref] wrote:
  

quoted

Hi Tejun,

On Wed, 3 Mar 2021 10:44:28 -0500, Tejun Heo [off-list ref] wrote:
  

quoted

On Sat, Feb 27, 2021 at 02:01:23PM -0800, Jacob Pan wrote:    

quoted

IOASIDs are used to associate DMA requests with virtual address
spaces. They are a system-wide limited resource made available to
the userspace applications. Let it be VMs or user-space device
drivers.

This RFC patch introduces a cgroup controller to address the
following problems:
1. Some user applications exhaust all the available IOASIDs thus
depriving others of the same host.
2. System admins need to provision VMs based on their needs for
IOASIDs, e.g. the number of VMs with assigned devices that perform
DMA requests with PASID.      

Please take a look at the proposed misc controller:

 http://lkml.kernel.org/r/20210302081705.1990283-2-vipinsh-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org

Would that fit your bill?    

The interface definitely can be reused. But IOASID has a different
behavior in terms of migration and ownership checking. I guess SEV key
IDs are not tied to a process whereas IOASIDs are. Perhaps this can be
solved by adding
+	.can_attach	= ioasids_can_attach,
+	.cancel_attach	= ioasids_cancel_attach,
Let me give it a try and come back.
  

While I am trying to fit the IOASIDs cgroup in to the misc cgroup
proposal. I'd like to have a direction check on whether this idea of
using cgroup for IOASID/PASID resource management is viable.  

Yes, even for host SVA it would be good to have a cgroup. Currently the
number of shared address spaces is naturally limited by number of
processes, which can be controlled with rlimit and cgroup. But on Arm the
hardware limit on shared address spaces is 64k (number of ASIDs), easily
exhausted with the default PASID and PID limits. So a cgroup for managing
this resource is more than welcome.

It looks like your current implementation is very dependent on
IOASID_SET_TYPE_MM?  I'll need to do more reading about cgroup to see how
easily it can be adapted to host SVA which uses IOASID_SET_TYPE_NULL.

Right, I was assuming have three use cases of IOASIDs:
1. host supervisor SVA (not a concern, just one init_mm to bind)
2. host user SVA, either one IOASID per process or perhaps some private
IOASID for private address space
3. VM use for guest SVA, each IOASID is bound to a guest process

My current cgroup proposal applies to #3 with IOASID_SET_TYPE_MM, which is
allocated by the new /dev/ioasid interface.

For #2, I was thinking you can limit the host process via PIDs cgroup? i.e.
limit fork.

That works but isn't perfect, because the hardware resource of shared
address spaces can be much lower that PID limit - 16k ASIDs on Arm. To
allow an admin to fairly distribute that resource we could introduce
another cgroup just to limit the number of shared address spaces, but
limiting the number of IOASIDs does the trick.

So the host IOASIDs are currently allocated from the system pool
with quota of chosen by iommu_sva_init() in my patch, 0 means unlimited use
whatever is available. https://lkml.org/lkml/2021/2/28/18

Yes that's sensible, but it would be good to plan the cgroup user
interface to work for #2 as well, even if we don't implement it right
away.

Thanks,
Jean