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

From: Jason Gunthorpe <jgg@nvidia.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	dmaengine@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	vkoul@kernel.org, robin.murphy@arm.com, will@kernel.org,
	Yi Liu <yi.l.liu@intel.com>, Dave Jiang <dave.jiang@intel.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Raj Ashok <ashok.raj@intel.com>,
	Eric Auger <eric.auger@redhat.com>
Subject: Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for attach_dev_pasid
Date: Wed, 11 May 2022 14:00:25 -0300	[thread overview]
Message-ID: <20220511170025.GF49344@nvidia.com> (raw)
In-Reply-To: <20220511100216.7615e288@jacob-builder>

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.

> 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.

Jason