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

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Message-ID: <20220511100216.7615e288@jacob-builder>
Date:   Wed, 11 May 2022 10:02:16 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.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>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for
 attach_dev_pasid

Hi Jason,

On Wed, 11 May 2022 13:12:37 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> 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
> 
I have tried to have its own ops but there are complications around
checking if a domain has ops. It would be a logic thing to clean up next.

> > 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.
> 
I am not following,  here are the PASIDs for devTLB flush which is per
device. Why group?
We could retrieve PASIDs from the device PASID table but xa would be more
efficient.

> > > > 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.
Perhaps some code to clarify, we have
sva_domain_ops.dev_attach_pasid() = intel_svm_attach_dev_pasid;
default_domain_ops.dev_attach_pasid() = intel_iommu_attach_dev_pasid;

Consolidate pasid programming into dev_set_pasid() then called by both
intel_svm_attach_dev_pasid() and intel_iommu_attach_dev_pasid(), right?


Thanks,

Jacob