linux-kernel - Re: [PATCH v13 07/13] iommu/vt-d: Add SVA domain support

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Message-ID: <075278e0-77ce-2361-8ded-6cd6bb20216f@linux.intel.com>
Date:   Fri, 23 Sep 2022 10:21:51 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v13 07/13] iommu/vt-d: Add SVA domain support

On 2022/9/22 23:49, Jason Gunthorpe wrote:
> On Tue, Sep 06, 2022 at 08:44:52PM +0800, Lu Baolu wrote:
>> +static void intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
>> +{
>> +	struct intel_iommu *iommu = device_to_iommu(dev, NULL, NULL);
>> +	struct iommu_domain *domain;
>> +
>> +	/* Domain type specific cleanup: */
>> +	domain = iommu_get_domain_for_dev_pasid(dev, pasid, 0);
>> +	if (domain) {
>> +		switch (domain->type) {
>> +		case IOMMU_DOMAIN_SVA:
>> +			intel_svm_remove_dev_pasid(dev, pasid);
>> +			break;
>> +		default:
>> +			/* should never reach here */
>> +			WARN_ON(1);
>> +			break;
> 
> This is eventually going to need a lot more cleaning up to split out
> the PASID from the SVM stuff.
> 
> SVA should *only* be a set of predefined handlers (in the core code!)
> for the generic PRI mechanism, it shouldn't be entangled deeply into
> PASID or the drivers like this.
> 
> When we get done with this, the flow should have the core code attach
> a SVA domain to a PASID with PRI enabled and the core code should
> supply a generic PRI implementation that does the mmu_notifier
> stuff.

Yes. Agreed.

At the beginning of this project, I wanted to consolidate the mm
notifications into the core. However, ARM SMMUv3 and Intel handle the mm
notifications a little differently. Then I decided to do this work
separately from the current series.

> 
> Also, stuff like this:
> 
> 				/* We mandate that no page faults may be outstanding
> 				 * for the PASID when intel_svm_unbind_mm() is called.
> 				 * If that is not obeyed, subtle errors will happen.
> 				 * Let's make them less subtle... */
> 
> Are going to be problematic for VFIO as well. In a VFIO world the
> entire RID and its entire PASID table has to be owned by VFIO and
> never shared - so these sequencing issues should be solvable.
> 
> But this is all for further series..

Yes. All these sound interesting future series.

> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

I'm very appreciated for your time.

Best regards,
baolu