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

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Message-ID: <20220510172309.3c4e7512@jacob-builder>
Date:   Tue, 10 May 2022 17:23:09 -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 Tue, 10 May 2022 20:21:21 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:

> On Tue, May 10, 2022 at 02:07:01PM -0700, Jacob Pan wrote:
> > +static int intel_iommu_attach_dev_pasid(struct iommu_domain *domain,
> > +					struct device *dev,
> > +					ioasid_t pasid)
> > +{
> > +	struct device_domain_info *info = dev_iommu_priv_get(dev);
> > +	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
> > +	struct intel_iommu *iommu = info->iommu;
> > +	unsigned long flags;
> > +	int ret = 0;
> > +
> > +	if (!sm_supported(iommu) || !info)
> > +		return -ENODEV;
> > +
> > +	spin_lock_irqsave(&device_domain_lock, flags);
> > +	/*
> > +	 * If the same device already has a PASID attached, just
> > return.
> > +	 * DMA layer will return the PASID value to the caller.
> > +	 */
> > +	if (pasid != PASID_RID2PASID && info->pasid) {  
> 
> Why check for PASID == 0 like this? Shouldn't pasid == 0 be rejected
> as an invalid argument?
Right, I was planning on reuse the attach function for RIDPASID as clean
up, but didn't include here. Will fix.

> 
> > +		if (info->pasid == pasid)
> > +			ret = 0;  
> 
> Doesn't this need to check that the current domain is the requested
> domain as well? How can this happen anyhow - isn't it an error to
> double attach?
> 
> > diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> > index 5af24befc9f1..55845a8c4f4d 100644
> > +++ b/include/linux/intel-iommu.h
> > @@ -627,6 +627,7 @@ struct device_domain_info {
> >  	struct intel_iommu *iommu; /* IOMMU used by this device */
> >  	struct dmar_domain *domain; /* pointer to domain */
> >  	struct pasid_table *pasid_table; /* pasid table */
> > +	ioasid_t pasid; /* DMA request with PASID */  
> 
> And this seems wrong - the DMA API is not the only user of
> attach_dev_pasid, so there should not be any global pasid for the
> device.
> 
True but the attach_dev_pasid() op is domain type specific. i.e. DMA API
has its own attach_dev_pasid which is different than sva domain
attach_dev_pasid().
device_domain_info is only used by DMA API.

> I suspect this should be a counter of # of pasid domains attached so
> that the special flush logic triggers
> 
This field is only used for devTLB, so it is per domain-device. struct
device_domain_info is allocated per device-domain as well. Sorry, I might
have totally missed your point.

> And rely on the core code to worry about assigning only one domain per
> pasid - this should really be a 'set' function.
> 
Yes, in this set the core code (in dma-iommu.c) only assign one PASID per
DMA domain type.

Are you suggesting the dma-iommu API should be called
iommu_set_dma_pasid instead of iommu_attach_dma_pasid?

Thanks a lot for the quick review!

Jacob