linux-kernel - Re: [PATCH 2/2] iommu/ioasid: Remove custom IOASID allocator

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Message-ID: <Y+rLqg66BBPsfsRK@nvidia.com>
Date:   Mon, 13 Feb 2023 19:45:46 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Robin Murphy <robin.murphy@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Raj Ashok <ashok.raj@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH 2/2] iommu/ioasid: Remove custom IOASID allocator

On Mon, Feb 13, 2023 at 03:43:45PM -0800, Jacob Pan wrote:
> Hi Jason,
> 
> On Mon, 13 Feb 2023 19:18:51 -0400, Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > On Mon, Feb 13, 2023 at 01:44:02PM -0800, Jacob Pan wrote:
> > > > Your DMA API PASID thing will simply need one new API to alloc/free a
> > > > PASID from the iommu_global_pasid_ida  
> > > It should satisfy what we need right now.
> > > Just wondering if we were to do resource management of global PASIDs,
> > > say with the new misc cgroup controller, do we plan to expand in iommu
> > > sva code? If yes, do we keep DMA API PASID in a separate range/set?  
> > 
> > I would say all shared PASIDs held by userspace should be captured by
> > by a resource limit, it doesn't matter if they are global PASIDs or
> > device local shared PASIDs.
> agreed, I was just thinking in-kernel DMA PASID is not held by userspace,
> might be good to keep them in separate pool, thus keeping ioasid_set.

Then you just don't charge a cgroup when you get these, you won't have
a cgroup anyhow in that context.

The "ioasid_set" is really the xarray, and you don't have an option to
use two xarrays with the same RID, so we definately wouldn't have two
pools.

> > So if a cgroup comes it is just a matter of putting charges in the
> > right place which is auditable by looking at calls to attach pasid
> > functions.
> shouldn't we charge cg during allocation? Or it might be too early for
> iommufd so we have to wait  until attach?

We need to sort this all out. I would expect that iommufd will have an
allocation API.

Jason