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

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Message-ID: <20220511102521.6b7c578c@jacob-builder>
Date:   Wed, 11 May 2022 10:25:21 -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 14:00:25 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> On Wed, May 11, 2022 at 10:02:16AM -0700, Jacob Pan wrote:
> > > > 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?  
> 
> Because group is where the core code stores it.
I see, with singleton group. I guess I can let dma-iommu code call

iommu_attach_dma_pasid {
	iommu_attach_device_pasid();
Then the PASID will be stored in the group xa.
The flush code can retrieve PASIDs from device_domain_info.device -> group
-> pasid_array.
Thanks for pointing it out, I missed the new pasid_array.
> 
> > 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;  
> 
> Yes, keep that structure
>  
> > Consolidate pasid programming into dev_set_pasid() then called by both
> > intel_svm_attach_dev_pasid() and intel_iommu_attach_dev_pasid(), right?
> >  
> 
> I was only suggesting that really dev_attach_pasid() op is misnamed,
> it should be called set_dev_pasid() and act like a set, not a paired
> attach/detach - same as the non-PASID ops.
> 
Got it. Perhaps another patch to rename, Baolu?


Thanks,

Jacob