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From: Jean-Philippe Brucker <jean-philippe@linaro.org>
To: Will Deacon <will@kernel.org>
Cc: mark.rutland@arm.com, devicetree@vger.kernel.org,
	jacob.jun.pan@linux.intel.com,
	Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
	joro@8bytes.org, linux-kernel@vger.kernel.org,
	eric.auger@redhat.com, iommu@lists.linux-foundation.org,
	robh+dt@kernel.org, robin.murphy@arm.com,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 6/8] iommu/arm-smmu-v3: Support auxiliary domains
Date: Thu, 19 Sep 2019 17:06:34 +0200
Message-ID: <20190919150634.GE1013538@lophozonia> (raw)
In-Reply-To: <20190626175959.ubxvb2qn4taclact@willie-the-truck>

On Wed, Jun 26, 2019 at 06:59:59PM +0100, Will Deacon wrote:
> > @@ -666,8 +668,14 @@ struct arm_smmu_domain {
> >  
> >  	struct iommu_domain		domain;
> >  
> > +	/* Unused in aux domains */
> >  	struct list_head		devices;
> >  	spinlock_t			devices_lock;
> > +
> > +	/* Auxiliary domain stuff */
> > +	struct arm_smmu_domain		*parent;
> > +	ioasid_t			ssid;
> > +	unsigned long			aux_nr_devs;
> 
> Maybe use a union to avoid comments about what is used/unused?

OK

> > +static void arm_smmu_aux_detach_dev(struct iommu_domain *domain, struct device *dev)
> > +{
> > +	struct iommu_domain *parent_domain;
> > +	struct arm_smmu_domain *parent_smmu_domain;
> > +	struct arm_smmu_master *master = dev_to_master(dev);
> > +	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
> > +
> > +	if (!arm_smmu_dev_feature_enabled(dev, IOMMU_DEV_FEAT_AUX))
> > +		return;
> > +
> > +	parent_domain = iommu_get_domain_for_dev(dev);
> > +	if (!parent_domain)
> > +		return;
> > +	parent_smmu_domain = to_smmu_domain(parent_domain);
> > +
> > +	mutex_lock(&smmu_domain->init_mutex);
> > +	if (!smmu_domain->aux_nr_devs)
> > +		goto out_unlock;
> > +
> > +	if (!--smmu_domain->aux_nr_devs) {
> > +		arm_smmu_write_ctx_desc(parent_smmu_domain, smmu_domain->ssid,
> > +					NULL);
> > +		/*
> > +		 * TLB doesn't need invalidation since accesses from the device
> > +		 * can't use this domain's ASID once the CD is clear.
> > +		 *
> > +		 * Sadly that doesn't apply to ATCs, which are PASID tagged.
> > +		 * Invalidate all other devices as well, because even though
> > +		 * they weren't 'officially' attached to the auxiliary domain,
> > +		 * they could have formed ATC entries.
> > +		 */
> > +		arm_smmu_atc_inv_domain(smmu_domain, 0, 0);
> 
> I've been struggling to understand the locking here, since both
> arm_smmu_write_ctx_desc and arm_smmu_atc_inv_domain take and release the
> devices_lock for the domain. Is there not a problem with devices coming and
> going in-between the two calls?

Yes, I need to think about this more. I bet there are plenty more issues
like this. For example I don't think I currently prevent the parent
domain from disappearing while auxiliary domains are attached.

> >  static struct iommu_ops arm_smmu_ops = {
> >  	.capable		= arm_smmu_capable,
> >  	.domain_alloc		= arm_smmu_domain_alloc,
> > @@ -2539,6 +2772,13 @@ static struct iommu_ops arm_smmu_ops = {
> >  	.of_xlate		= arm_smmu_of_xlate,
> >  	.get_resv_regions	= arm_smmu_get_resv_regions,
> >  	.put_resv_regions	= arm_smmu_put_resv_regions,
> > +	.dev_has_feat		= arm_smmu_dev_has_feature,
> > +	.dev_feat_enabled	= arm_smmu_dev_feature_enabled,
> > +	.dev_enable_feat	= arm_smmu_dev_enable_feature,
> > +	.dev_disable_feat	= arm_smmu_dev_disable_feature,
> 
> Why can't we use the existing ->capable and ->dev_{get,set}_attr callbacks
> for this?

->capable isn't very useful because it applies to all SMMUs in the
system. The existing ->{get,set}_attr callbacks apply to an
iommu_domain. I think the main reason for doing it on endpoints was that
it would be tedious to keep track of capabilities when attaching and
detaching devices to a domain, especially for drivers that allow
multiple IOMMUs per domain [1]. There were more discussions, and in the
end we agreed on this API for device attributes [2].

Thanks,
Jean

[1] https://lore.kernel.org/lkml/aa1ff748-c2ec-acc0-f1d9-cdff2b131e58@linux.intel.com/
[2] https://lore.kernel.org/linux-iommu/20181207102926.GM16835@8bytes.org/


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  parent reply index

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-10 18:47 [PATCH 0/8] iommu: Add auxiliary domain and PASID support to Arm SMMUv3 Jean-Philippe Brucker
2019-06-10 18:47 ` [PATCH 1/8] iommu: Add I/O ASID allocator Jean-Philippe Brucker
2019-06-11  9:36   ` Jonathan Cameron
2019-06-11 14:35     ` Jean-Philippe Brucker
2019-06-11 18:13       ` Jacob Pan
2019-06-18 14:22         ` Jean-Philippe Brucker
2019-06-18 17:05           ` Jacob Pan
2019-06-19 14:26             ` Jean-Philippe Brucker
2019-06-11 12:26   ` Jacob Pan
2019-06-11 14:37     ` Jean-Philippe Brucker
2019-06-11 17:10       ` Jacob Pan
2019-06-12 11:30         ` Jean-Philippe Brucker
2019-06-10 18:47 ` [PATCH 2/8] dt-bindings: document PASID property for IOMMU masters Jean-Philippe Brucker
2019-07-08  7:58   ` Auger Eric
2019-06-10 18:47 ` [PATCH 3/8] iommu/arm-smmu-v3: Support platform SSID Jean-Philippe Brucker
2019-06-11  9:42   ` Jonathan Cameron
2019-06-11 14:35     ` Jean-Philippe Brucker
2019-06-18 18:08   ` Will Deacon
2019-06-19 11:53     ` Jean-Philippe Brucker
2019-07-08  7:58   ` Auger Eric
2019-09-19 14:51     ` Jean-Philippe Brucker
2019-06-10 18:47 ` [PATCH 4/8] iommu/arm-smmu-v3: Add support for Substream IDs Jean-Philippe Brucker
2019-06-11 10:19   ` Jonathan Cameron
2019-06-11 14:35     ` Jean-Philippe Brucker
2019-06-26 18:00   ` Will Deacon
2019-07-04  9:33     ` Jean-Philippe Brucker
2019-09-19 14:57     ` Jean-Philippe Brucker
2019-07-08 15:31   ` Auger Eric
2019-09-19 15:01     ` Jean-Philippe Brucker
2019-06-10 18:47 ` [PATCH 5/8] iommu/arm-smmu-v3: Add second level of context descriptor table Jean-Philippe Brucker
2019-06-11 10:24   ` Jonathan Cameron
2019-07-08 15:13   ` Auger Eric
2019-06-10 18:47 ` [PATCH 6/8] iommu/arm-smmu-v3: Support auxiliary domains Jean-Philippe Brucker
2019-06-26 17:59   ` Will Deacon
2019-07-05 16:29     ` Jean-Philippe Brucker
2019-09-19 15:06     ` Jean-Philippe Brucker [this message]
2019-06-10 18:47 ` [PATCH 7/8] iommu/arm-smmu-v3: Improve add_device() error handling Jean-Philippe Brucker
2019-07-08  7:58   ` Auger Eric
2019-06-10 18:47 ` [PATCH 8/8] iommu/arm-smmu-v3: Add support for PCI PASID Jean-Philippe Brucker
2019-06-11 10:45   ` Jonathan Cameron
2019-06-11 14:35     ` Jean-Philippe Brucker
2019-07-08  7:58   ` Auger Eric
2019-09-19 15:10     ` Jean-Philippe Brucker

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