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

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Date:   Mon, 13 Feb 2023 19:30:26 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     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>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH 2/2] iommu/ioasid: Remove custom IOASID allocator

On Mon, Feb 13, 2023 at 10:34:55AM -0800, Jacob Pan wrote:
> > On a related note, it looks like 100b8a14a370 ("iommu/vt-d: Add pasid
> > private data helpers") removed the last user of ioasid_set_data(). I guess
> > that could be dropped too, unless you plan to still use it?
> > 
> You are right, will remove.
> I was planning on the other way around which will convert VT-d's private
> pasid data helpers to common ioasid code, but when I look closer the
> private pasid xa is just holding a list of pasid/mm which could be per iommu
> not global. Another cleanup I suppose.

Yes that should probably be common to SVA. I'm planning to take another
look at SVA on the SMMU side following the recent API changes, and from a
quick glance the problem that VT-d's private helpers solves is common.

> > We could also merge ioasid.c into iommu-sva.c at this point, since I
> > haven't seen any interest for having multiple IOASID sets on Arm, but I'm
> > not sure what the current plan is for vSVA on x86.
> VT-d do plan to use global PASIDs for DMA API with PASIDs since the
> work submited via ENQCMDS must use a PASID must != RIDPASID.
> https://lore.kernel.org/lkml/20220518182120.1136715-1-jacob.jun.pan@linux.intel.com/T/
> 
> So I was thinking a separate ioasid_set for devices that allocates global
> PASIDs for DMA API usage. ioasid_set will be useful here for limiting
> lookup and resource management. e.g. PASIDs used under in-kernel DMA API
> are not subject to cgroups.

Ok. Yes that was the goal of ioasid_set

Thanks,
Jean