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Date:   Mon, 27 Apr 2020 13:34:09 -0700
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     "Tian, Kevin" <kevin.tian@intel.com>
Cc:     Lu Baolu <baolu.lu@linux.intel.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Eric Auger <eric.auger@redhat.com>,
        "Liu, Yi L" <yi.l.liu@intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Alex Williamson" <alex.williamson@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jonathan Cameron <jic23@kernel.org>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v12 4/8] iommu/vt-d: Add bind guest PASID support
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        <AADFC41AFE54684AB9EE6CBC0274A5D19D8A0D03@SHSMSX104.ccr.corp.intel.com>
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On Fri, 24 Apr 2020 10:47:45 +0000
"Tian, Kevin" <kevin.tian@intel.com> wrote:

> > From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Sent: Wednesday, April 22, 2020 2:53 AM
> > 
> > When supporting guest SVA with emulated IOMMU, the guest PASID
> > table is shadowed in VMM. Updates to guest vIOMMU PASID table
> > will result in PASID cache flush which will be passed down to
> > the host as bind guest PASID calls.  
> 
> Above description is not accurate. Guest PASID table updates don't
> 'result in' PASID cache flush automatically. What about:
> --
> The guest needs to invalidate the PASID cache for any update to
> guest PASID table. Those invalidation requests are intercepted
> by the VMM and passed down to the host as binding guest PASID
> calls.
> --
It is good to add more details, thanks.

> > 
> > For the SL page tables, it will be harvested from device's
> > default domain (request w/o PASID), or aux domain in case of
> > mediated device.
> > 
> >     .-------------.  .---------------------------.
> >     |   vIOMMU    |  | Guest process CR3, FL only|
> >     |             |  '---------------------------'
> >     .----------------/
> >     | PASID Entry |--- PASID cache flush -
> >     '-------------'                       |
> >     |             |                       V
> >     |             |                CR3 in GPA
> >     '-------------'
> > Guest
> > ------| Shadow |--------------------------|--------
> >       v        v                          v
> > Host
> >     .-------------.  .----------------------.
> >     |   pIOMMU    |  | Bind FL for GVA-GPA  |
> >     |             |  '----------------------'
> >     .----------------/  |
> >     | PASID Entry |     V (Nested xlate)
> >     '----------------\.------------------------------.
> >     |             |   |SL for GPA-HPA, default domain|
> >     |             |   '------------------------------'
> >     '-------------'
> > Where:
> >  - FL = First level/stage one page tables
> >  - SL = Second level/stage two page tables
> > 
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Signed-off-by: Liu, Yi L <yi.l.liu@linux.intel.com>
> > ---
> >  drivers/iommu/intel-iommu.c |   4 +
> >  drivers/iommu/intel-svm.c   | 204
> > ++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/intel-iommu.h |   8 +-
> >  include/linux/intel-svm.h   |  17 ++++
> >  4 files changed, 232 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index 9c01e391a931..8862d6b0ef21
> > 100644 --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -6179,6 +6179,10 @@ const struct iommu_ops intel_iommu_ops = {
> >  	.dev_disable_feat	= intel_iommu_dev_disable_feat,
> >  	.is_attach_deferred	=
> > intel_iommu_is_attach_deferred, .pgsize_bitmap		=
> > INTEL_IOMMU_PGSIZES, +#ifdef CONFIG_INTEL_IOMMU_SVM
> > +	.sva_bind_gpasid	= intel_svm_bind_gpasid,
> > +	.sva_unbind_gpasid	= intel_svm_unbind_gpasid,
> > +#endif
> >  };
> > 
> >  static void quirk_iommu_igfx(struct pci_dev *dev)
> > diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> > index 2998418f0a38..69b2070b843d 100644
> > --- a/drivers/iommu/intel-svm.c
> > +++ b/drivers/iommu/intel-svm.c
> > @@ -226,6 +226,210 @@ static LIST_HEAD(global_svm_list);
> >  	list_for_each_entry((sdev), &(svm)->devs, list)	\
> >  		if ((d) != (sdev)->dev) {} else
> > 
> > +static inline void intel_svm_free_if_empty(struct intel_svm *svm,
> > u64 pasid) +{
> > +	if (list_empty(&svm->devs)) {
> > +		ioasid_set_data(pasid, NULL);
> > +		kfree(svm);
> > +	}
> > +}  
> 
> Do we really need a function form instead of putting the 4 lines
> directly after the 'out' label?
> 
it is more readable and good for code sharing.

> > +
> > +int intel_svm_bind_gpasid(struct iommu_domain *domain, struct
> > device *dev,
> > +			  struct iommu_gpasid_bind_data *data)
> > +{
> > +	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
> > +	struct dmar_domain *dmar_domain;
> > +	struct intel_svm_dev *sdev;
> > +	struct intel_svm *svm;
> > +	int ret = 0;
> > +
> > +	if (WARN_ON(!iommu) || !data)
> > +		return -EINVAL;  
> 
> well, why not checking !dev together?
This is kernel API, unlike iommu and data caller fills in dev directly.

> 
> > +
> > +	if (data->version != IOMMU_GPASID_BIND_VERSION_1 ||
> > +	    data->format != IOMMU_PASID_FORMAT_INTEL_VTD)
> > +		return -EINVAL;
> > +
> > +	if (dev_is_pci(dev)) {
> > +		/* VT-d supports devices with full 20 bit PASIDs
> > only */
> > +		if (pci_max_pasids(to_pci_dev(dev)) != PASID_MAX)
> > +			return -EINVAL;
> > +	} else {
> > +		return -ENOTSUPP;
> > +	}
> > +
> > +	/*
> > +	 * We only check host PASID range, we have no knowledge to
> > check
> > +	 * guest PASID range.
> > +	 */
> > +	if (data->hpasid <= 0 || data->hpasid >= PASID_MAX)
> > +		return -EINVAL;
> > +
> > +	dmar_domain = to_dmar_domain(domain);
> > +
> > +	mutex_lock(&pasid_mutex);
> > +	svm = ioasid_find(NULL, data->hpasid, NULL);
> > +	if (IS_ERR(svm)) {
> > +		ret = PTR_ERR(svm);
> > +		goto out;
> > +	}
> > +
> > +	if (svm) {
> > +		/*
> > +		 * If we found svm for the PASID, there must be at
> > +		 * least one device bond, otherwise svm should be
> > freed.
> > +		 */
> > +		if (WARN_ON(list_empty(&svm->devs))) {
> > +			ret = -EINVAL;
> > +			goto out;
> > +		}
> > +
> > +		for_each_svm_dev(sdev, svm, dev) {
> > +			/* In case of multiple sub-devices of the
> > same pdev
> > +			 * assigned, we should allow multiple bind
> > calls with
> > +			 * the same PASID and pdev.
> > +			 */
> > +			sdev->users++;
> > +			goto out;  
> 
> in last review Eric raised the open about what about binding the same
> PASID to the same pdev multiple times. We discussed that should be
> disallowed. Here can you check whether aux_domain is enabled on pdev
> to restrict multiple-binding only for sub-devices?
Why aux_domain is sufficient? A pdev could have aux_domain enabled but
still bind pdev many times more than its mdevs.

Either we allow multiple bind or not.

> 
> > +		}
> > +	} else {
> > +		/* We come here when PASID has never been bond to a
> > device. */
> > +		svm = kzalloc(sizeof(*svm), GFP_KERNEL);
> > +		if (!svm) {
> > +			ret = -ENOMEM;
> > +			goto out;
> > +		}
> > +		/* REVISIT: upper layer/VFIO can track host
> > process that bind
> > +		 * the PASID. ioasid_set = mm might be sufficient
> > for vfio to
> > +		 * check pasid VMM ownership. We can drop the
> > following line
> > +		 * once VFIO and IOASID set check is in place.
> > +		 */  
> 
> there is no check below this comment. Following lines are simply
> initializing the svm fields.
> 
What it meant to say is that once IOASID set is checked in VFIO layer,
we can drop the assignment of svm->mm, IOMMU driver will not check.

You are right, this is just a place holder to help handle many moving
pieces.

> > +		svm->mm = get_task_mm(current);
> > +		svm->pasid = data->hpasid;
> > +		if (data->flags & IOMMU_SVA_GPASID_VAL) {
> > +			svm->gpasid = data->gpasid;
> > +			svm->flags |= SVM_FLAG_GUEST_PASID;
> > +		}
> > +		ioasid_set_data(data->hpasid, svm);
> > +		INIT_LIST_HEAD_RCU(&svm->devs);
> > +		mmput(svm->mm);
> > +	}
> > +	sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
> > +	if (!sdev) {
> > +		/*
> > +		 * If this is a new PASID that never bond to a
> > device, then
> > +		 * the device list must be empty which indicates
> > struct svm
> > +		 * was allocated in this function.
> > +		 */
> > +		intel_svm_free_if_empty(svm, data->hpasid);
> > +		ret = -ENOMEM;
> > +		goto out;
> > +	}
> > +	sdev->dev = dev;
> > +	sdev->users = 1;
> > +
> > +	/* Set up device context entry for PASID if not enabled
> > already */
> > +	ret = intel_iommu_enable_pasid(iommu, sdev->dev);
> > +	if (ret) {
> > +		dev_err_ratelimited(dev, "Failed to enable PASID
> > capability\n");  
> 
> print hpasid 

OK, sounds good.
> 
> > +		kfree(sdev);
> > +		intel_svm_free_if_empty(svm, data->hpasid);
> > +		goto out;
> > +	}
> > +
> > +	/*
> > +	 * PASID table is per device for better security.
> > Therefore, for
> > +	 * each bind of a new device even with an existing PASID,
> > we need to
> > +	 * call the nested mode setup function here.
> > +	 */
> > +	spin_lock(&iommu->lock);
> > +	ret = intel_pasid_setup_nested(iommu,
> > +				       dev,
> > +				       (pgd_t *)data->gpgd,
> > +				       data->hpasid,
> > +				       &data->vtd,
> > +				       dmar_domain,
> > +				       data->addr_width);
> > +	if (ret) {
> > +		dev_err_ratelimited(dev, "Failed to set up PASID
> > %llu in nested mode, Err %d\n",
> > +				    data->hpasid, ret);
> > +		/*
> > +		 * PASID entry should be in cleared state if
> > nested mode
> > +		 * set up failed. So we only need to clear IOASID
> > tracking
> > +		 * data such that free call will succeed.
> > +		 */
> > +		kfree(sdev);
> > +		intel_svm_free_if_empty(svm, data->hpasid);
> > +		spin_unlock(&iommu->lock);
> > +		goto out;
> > +	}
> > +	spin_unlock(&iommu->lock);  
> 
> spin_unlock can be moved before if(ret)?
Yes, good point. We can combine the unlock.

> 
> > +	svm->flags |= SVM_FLAG_GUEST_MODE;
> > +
> > +	init_rcu_head(&sdev->rcu);
> > +	list_add_rcu(&sdev->list, &svm->devs);
> > + out:
> > +	mutex_unlock(&pasid_mutex);
> > +	return ret;
> > +}
> > +
> > +int intel_svm_unbind_gpasid(struct device *dev, int pasid)
> > +{
> > +	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
> > +	struct intel_svm_dev *sdev;
> > +	struct intel_svm *svm;
> > +	int ret = -EINVAL;
> > +
> > +	if (WARN_ON(!iommu))
> > +		return -EINVAL;
> > +
> > +	mutex_lock(&pasid_mutex);
> > +	svm = ioasid_find(NULL, pasid, NULL);
> > +	if (!svm) {
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> > +
> > +	if (IS_ERR(svm)) {
> > +		ret = PTR_ERR(svm);
> > +		goto out;
> > +	}
> > +
> > +	for_each_svm_dev(sdev, svm, dev) {
> > +		ret = 0;
> > +		sdev->users--;
> > +		if (!sdev->users) {
> > +			list_del_rcu(&sdev->list);
> > +			intel_pasid_tear_down_entry(iommu, dev,
> > svm-  
> > >pasid);  
> > +			intel_flush_svm_range_dev(svm, sdev, 0,
> > -1, 0);
> > +			/* TODO: Drain in flight PRQ for the PASID
> > since it
> > +			 * may get reused soon, we don't want to
> > +			 * confuse with its previous life.
> > +			 * intel_svm_drain_prq(dev, pasid);
> > +			 */
> > +			kfree_rcu(sdev, rcu);
> > +
> > +			if (list_empty(&svm->devs)) {
> > +				/*
> > +				 * We do not free the IOASID here
> > in that
> > +				 * IOMMU driver did not allocate
> > it.
> > +				 * Unlike native SVM, IOASID for
> > guest use was
> > +				 * allocated prior to the bind
> > call.
> > +				 * In any case, if the free call
> > comes before
> > +				 * the unbind, IOMMU driver will
> > get notified
> > +				 * and perform cleanup.
> > +				 */
> > +				ioasid_set_data(pasid, NULL);
> > +				kfree(svm);
> > +			}  
> 
> is it safer moving above empty check outside of the loop?
why? could you explain.

Note that this is not a loop.

> 
> > +		}
> > +		break;
> > +	}
> > +out:
> > +	mutex_unlock(&pasid_mutex);
> > +	return ret;
> > +}
> > +
> >  int intel_svm_bind_mm(struct device *dev, int *pasid, int flags,
> > struct svm_dev_ops *ops)
> >  {
> >  	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
> > diff --git a/include/linux/intel-iommu.h
> > b/include/linux/intel-iommu.h index 6da03f627ba3..c8ce2336f8d8
> > 100644 --- a/include/linux/intel-iommu.h
> > +++ b/include/linux/intel-iommu.h
> > @@ -706,7 +706,9 @@ struct dmar_domain *find_domain(struct device
> > *dev);
> >  extern void intel_svm_check(struct intel_iommu *iommu);
> >  extern int intel_svm_enable_prq(struct intel_iommu *iommu);
> >  extern int intel_svm_finish_prq(struct intel_iommu *iommu);
> > -
> > +int intel_svm_bind_gpasid(struct iommu_domain *domain, struct
> > device *dev,
> > +			  struct iommu_gpasid_bind_data *data);
> > +int intel_svm_unbind_gpasid(struct device *dev, int pasid);
> >  struct svm_dev_ops;
> > 
> >  struct intel_svm_dev {
> > @@ -723,9 +725,13 @@ struct intel_svm_dev {
> >  struct intel_svm {
> >  	struct mmu_notifier notifier;
> >  	struct mm_struct *mm;
> > +
> >  	struct intel_iommu *iommu;
> >  	int flags;
> >  	int pasid;
> > +	int gpasid; /* Guest PASID in case of vSVA bind with
> > non-identity host
> > +		     * to guest PASID mapping.
> > +		     */  
> 
> /* in case that guest PASID is different from host PASID */
OK, will do.

> 
> >  	struct list_head devs;
> >  	struct list_head list;
> >  };
> > diff --git a/include/linux/intel-svm.h b/include/linux/intel-svm.h
> > index d7c403d0dd27..c19690937540 100644
> > --- a/include/linux/intel-svm.h
> > +++ b/include/linux/intel-svm.h
> > @@ -44,6 +44,23 @@ struct svm_dev_ops {
> >   * do such IOTLB flushes automatically.
> >   */
> >  #define SVM_FLAG_SUPERVISOR_MODE	(1<<1)
> > +/*
> > + * The SVM_FLAG_GUEST_MODE flag is used when a guest process bind
> > to a device.
> > + * In this case the mm_struct is in the guest kernel or userspace,
> > its life  
> 
> this statement is confusing. We still have mm_struct in the host side
> to claim the ownership of a PASID.
> 
How about this:
/*
 * The SVM_FLAG_GUEST_MODE flag is used when a PASID bind is for guest
 * processes. Compared to the host bind, the primary differences are:
 * 1. mm life cycle management
 * 2. fault reporting
 */

> > + * cycle is managed by VMM and VFIO layer. For IOMMU driver, this
> > API  
> 
> why is a flag becoming an API?
> 
will refer as flag.

> > provides
> > + * means to bind/unbind guest CR3 with PASIDs allocated for a
> > device.
> > + */
> > +#define SVM_FLAG_GUEST_MODE	(1<<2)
> > +/*
> > + * The SVM_FLAG_GUEST_PASID flag is used when a guest has its own
> > PASID space,
> > + * which requires guest and host PASID translation at both
> > directions. We keep
> > + * track of guest PASID in order to provide lookup service to
> > device drivers.
> > + * One such example is a physical function (PF) driver that
> > supports mediated
> > + * device (mdev) assignment. Guest programming of mdev
> > configuration space can
> > + * only be done with guest PASID, therefore PF driver needs to
> > find the matching
> > + * host PASID to program the real hardware.  
> 
> I feel such example doesn't belong here, which is purely userspace
> policy. Here just describe what the flag is for should be sufficient.
> 
Will remove the example. How about this?

/*
 * The SVM_FLAG_GUEST_PASID flag is used when a guest has its own PASID space,
 * which requires guest and host PASID translation at both directions.
 */


> > + */
> > +#define SVM_FLAG_GUEST_PASID	(1<<3)
> > 
> >  #ifdef CONFIG_INTEL_IOMMU_SVM
> > 
> > --
> > 2.7.4  
> 
> Thanks
> Kevin
> 

[Jacob Pan]