On Wed, Mar 24, 2021 at 03:12:30PM -0700, Jacob Pan wrote:
> Hi Jason,
>
> On Wed, 24 Mar 2021 14:03:38 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
>
> > On Wed, Mar 24, 2021 at 10:02:46AM -0700, Jacob Pan wrote:
> > > > Also wondering about device driver allocating auxiliary domains for
> > > > their private use, to do iommu_map/unmap on private PASIDs (a clean
> > > > replacement to super SVA, for example). Would that go through the
> > > > same path as /dev/ioasid and use the cgroup of current task?
> > >
> > > For the in-kernel private use, I don't think we should restrict based on
> > > cgroup, since there is no affinity to user processes. I also think the
> > > PASID allocation should just use kernel API instead of /dev/ioasid. Why
> > > would user space need to know the actual PASID # for device private
> > > domains? Maybe I missed your idea?
> >
> > There is not much in the kernel that isn't triggered by a process, I
> > would be careful about the idea that there is a class of users that
> > can consume a cgroup controlled resource without being inside the
> > cgroup.
> >
> > We've got into trouble before overlooking this and with something
> > greenfield like PASID it would be best built in to the API to prevent
> > a mistake. eg accepting a cgroup or process input to the allocator.
> >
> Make sense. But I think we only allow charging the current cgroup, how about
> I add the following to ioasid_alloc():
>
> misc_cg = get_current_misc_cg();
> ret = misc_cg_try_charge(MISC_CG_RES_IOASID, misc_cg, 1);
> if (ret) {
> put_misc_cg(misc_cg);
> return ret;
> }
Does that allow PASID allocation during driver probe, in kernel_init or
modprobe context?
Thanks,
Jean
