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

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Date:   Mon, 13 Feb 2023 15:43:45 -0800
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.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>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH 2/2] iommu/ioasid: Remove custom IOASID allocator

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.

> 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?

Thanks,

Jacob