linux-kernel - Re: [PATCH 3/4] iommu/vt-d: Support PASID DMA for in-kernel usage

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Message-ID: <20211210185340.GI6385@nvidia.com>
Date:   Fri, 10 Dec 2021 14:53:40 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>, Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Barry Song <21cnbao@...il.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 3/4] iommu/vt-d: Support PASID DMA for in-kernel usage

On Fri, Dec 10, 2021 at 10:18:20AM -0800, Jacob Pan wrote:

> > If one device has 10 PASID's pointing to this domain you must flush
> > them all if that is what the HW requires.
> > 
> Yes. My point is that other than PASID 0 is a given, we must track the 10
> PASIDs to avoid wasted flush. It also depend on how TLBs are tagged and
> flush granularity available. But at the API level, should we support all the
> cases?

Yes, iommufd will expose all the cases to userspace and anything is
possible.

A scheme that can only attach a domain to one PASID is functionally
useless except for this IDXD problem, so don't make something so
broken.

Jason