linux-kernel - Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for attach_dev

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Message-ID: <20220511161237.GB49344@nvidia.com>
Date:   Wed, 11 May 2022 13:12:37 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>, dmaengine@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, vkoul@...nel.org,
        robin.murphy@....com, will@...nel.org, Yi Liu <yi.l.liu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for
 attach_dev_pasid

On Wed, May 11, 2022 at 08:35:18AM -0700, Jacob Pan wrote:

> > Huh? The intel driver shares the same ops between UNMANAGED and DMA -
> > and in general I do not think we should be putting special knowledge
> > about the DMA domains in the drivers. Drivers should continue to treat
> > them identically to UNMANAGED.
> > 
> OK, other than SVA domain, the rest domain types share the same default ops.
> I agree that the default ops should be the same for UNMANAGED, IDENTITY, and
> DMA domain types. Minor detail is that we need to treat IDENTITY domain
> slightly different when it comes down to PASID entry programming.

I would be happy if IDENTITY had its own ops, if that makes sense

> If not global, perhaps we could have a list of pasids (e.g. xarray) attached
> to the device_domain_info. The TLB flush logic would just go through the
> list w/o caring what the PASIDs are for. Does it make sense to you?

Sort of, but we shouldn't duplicate xarrays - the group already has
this xarray - need to find some way to allow access to it from the
driver.

> > > Are you suggesting the dma-iommu API should be called
> > > iommu_set_dma_pasid instead of iommu_attach_dma_pasid?  
> > 
> > No that API is Ok - the driver ops API should be 'set' not attach/detach
> > 
> Sounds good, this operation has little in common with
> domain_ops.dev_attach_pasid() used by SVA domain. So I will add a new
> domain_ops.dev_set_pasid()

What? No, their should only be one operation, 'dev_set_pasid' and it
is exactly the same as the SVA operation. It configures things so that
any existing translation on the PASID is removed and the PASID
translates according to the given domain.

SVA given domain or UNMANAGED given domain doesn't matter to the
higher level code. The driver should implement per-domain ops as
required to get the different behaviors.

Jason