RE: [PATCH V10 06/11] iommu/vt-d: Add bind guest PASID support

[Tian, Kevin]

> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Sent: Saturday, March 21, 2020 7:28 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.
> 
> 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@xxxxxxxxxxxxxxx>
> Signed-off-by: Liu, Yi L <yi.l.liu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/intel-iommu.c |   4 +
>  drivers/iommu/intel-svm.c   | 224
> ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/intel-iommu.h |   8 +-
>  include/linux/intel-svm.h   |  17 ++++
>  4 files changed, 252 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index e599b2537b1c..b1477cd423dd 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -6203,6 +6203,10 @@ 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 d7f2a5358900..47c0deb5ae56 100644
> --- a/drivers/iommu/intel-svm.c
> +++ b/drivers/iommu/intel-svm.c
> @@ -226,6 +226,230 @@ static LIST_HEAD(global_svm_list);
>  	list_for_each_entry((sdev), &(svm)->devs, list)	\
>  		if ((d) != (sdev)->dev) {} else
> 
> +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 *ddomain;

what about the full name e.g. dmar_domain? though a bit longer
but clearer than ddomain.

> +	struct intel_svm_dev *sdev;
> +	struct intel_svm *svm;
> +	int ret = 0;
> +
> +	if (WARN_ON(!iommu) || !data)
> +		return -EINVAL;
> +
> +	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 nor do we use the guest PASID.
> +	 */
> +	if (data->hpasid <= 0 || data->hpasid >= PASID_MAX)
> +		return -EINVAL;
> +
> +	ddomain = to_dmar_domain(domain);
> +
> +	/* Sanity check paging mode support match between host and guest
> */
> +	if (data->addr_width == ADDR_WIDTH_5LEVEL &&
> +	    !cap_5lp_support(iommu->cap)) {
> +		pr_err("Cannot support 5 level paging requested by
> guest!\n");
> +		return -EINVAL;
> +	}

-ENOTSUPP?

> +
> +	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;
> +		}
> +
> +		if (svm->mm == get_task_mm(current) &&
> +		    data->hpasid == svm->pasid &&
> +		    data->gpasid == svm->gpasid) {
> +			pr_warn("Cannot bind the same guest-host PASID for
> the same process\n");

Sorry I didnât get the rationale here. Isn't this branch is for binding the same
PASID to multiple devices? In that case definitely it is binding the same 
guest-host PASID for the same process. otherwise if hpasid is different then
you'll hit a different intel_svm, while if gpasid is different how you can use
one intel_svm to hold multiple gpasids?

I feel the error condition should be the opposite. and suppose SVM_FLAG_
GUEST_PASID should be verified before checking gpasid.

> +			mmput(svm->mm);
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +		mmput(current->mm);
> +
> +		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.

Does sub-device mean mdev? I didn't find such notation in current iommu
directory.

and to make it clearer, "In case of multiple mdevs of the same pdev assigned
to the same guest process".

> +			 */
> +			sdev->users++;
> +			goto out;
> +		}
> +	} 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.
> +		 */

Above message is unclear about what should be revisited. Does it describe
the current implementation or the expected revision in the future? 

> +		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 (list_empty(&svm->devs)) {
> +			ioasid_set_data(data->hpasid, NULL);
> +			kfree(svm);
> +		}
> +		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(dev, "Failed to enable PASID capability\n");
> +		kfree(sdev);
> +		/*
> +		 * If this this 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.
> +		 */

the comment better move to the 1st occurrence when sdev allocation
fails. or even better put it in out label...

> +		if (list_empty(&svm->devs)) {
> +			ioasid_set_data(data->hpasid, NULL);
> +			kfree(svm);
> +		}
> +		goto out;
> +	}
> +
> +	/*
> +	 * For guest bind, we need to set up PASID table entry as follows:
> +	 * - FLPM matches guest paging mode
> +	 * - turn on nested mode
> +	 * - SL guest address width matching
> +	 */

looks above just explains the internal detail of intel_pasid_setup_nested,
which is not necessary to be here.

> +	ret = intel_pasid_setup_nested(iommu,
> +				       dev,
> +				       (pgd_t *)data->gpgd,
> +				       data->hpasid,
> +				       &data->vtd,
> +				       ddomain,
> +				       data->addr_width);

It's worthy of an explanation here that setup_nested is required for
every device (even when they are sharing same intel_svm) because
we allocate pasid table per device. Otherwise I made a mistake to
think that only the 1st device bound to a new hpasid requires this
step. ð

> +	if (ret) {
> +		dev_err(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);
> +		if (list_empty(&svm->devs)) {
> +			ioasid_set_data(data->hpasid, NULL);
> +			kfree(svm);
> +		}
> +		goto out;
> +	}
> +	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);
> +			/* 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 PASID here until explicit call
> +				 * from VFIO to free. The PASID life cycle
> +				 * management is largely tied to VFIO
> management
> +				 * of assigned device life cycles. In case of
> +				 * guest exit without a explicit free PASID call,
> +				 * the responsibility lies in VFIO layer to free
> +				 * the PASIDs allocated for the guest.
> +				 * For security reasons, VFIO has to track the
> +				 * PASID ownership per guest anyway to
> ensure
> +				 * that PASID allocated by one guest cannot
> be
> +				 * used by another.

As commented in other patches, VFIO is only one example user of this API... 

> +				 */
> +				ioasid_set_data(pasid, NULL);
> +				kfree(svm);
> +			}
> +		}
> +		break;
> +	}

what about no dev match? an -EINVAL is also required then.

> +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 eda1d6687144..85b05120940e 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -681,7 +681,9 @@ 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);
> -
> +extern int intel_svm_bind_gpasid(struct iommu_domain *domain,
> +		struct device *dev, struct iommu_gpasid_bind_data *data);
> +extern int intel_svm_unbind_gpasid(struct device *dev, int pasid);
>  struct svm_dev_ops;
> 
>  struct intel_svm_dev {
> @@ -698,9 +700,13 @@ 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.
> +		     */

we don't need to highlight identity or non-identity thing, since either way 
shares the same infrastructure here and it is not the knowledge that the
kernel driver should assume

>  	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
> + * cycle is managed by VMM and VFIO layer. For IOMMU driver, this API
> 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.
> + */
> +#define SVM_FLAG_GUEST_PASID	(1<<3)
> 
>  #ifdef CONFIG_INTEL_IOMMU_SVM
> 
> --
> 2.7.4