Date:   Tue, 30 Apr 2019 09:05:01 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v2 15/19] iommu/vt-d: Add bind guest PASID support



On 4/29/19 5:25 PM, Jacob Pan wrote:
> On Fri, 26 Apr 2019 18:15:27 +0200
> Auger Eric <eric.auger@...hat.com> wrote:
> 
>> Hi Jacob,
>>
>> On 4/24/19 1:31 AM, Jacob Pan wrote:
>>> 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@...ux.intel.com>
>>> Signed-off-by: Liu, Yi L <yi.l.liu@...ux.intel.com>
>>> ---
>>>  drivers/iommu/intel-iommu.c |   4 +
>>>  drivers/iommu/intel-svm.c   | 174
>>> ++++++++++++++++++++++++++++++++++++++++++++
>>> include/linux/intel-iommu.h |  10 ++- include/linux/intel-svm.h
>>> |   7 ++ 4 files changed, 193 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/iommu/intel-iommu.c
>>> b/drivers/iommu/intel-iommu.c index 77bbe1b..89989b5 100644
>>> --- a/drivers/iommu/intel-iommu.c
>>> +++ b/drivers/iommu/intel-iommu.c
>>> @@ -5768,6 +5768,10 @@ const struct iommu_ops intel_iommu_ops = {
>>>  	.dev_enable_feat	= intel_iommu_dev_enable_feat,
>>>  	.dev_disable_feat	= intel_iommu_dev_disable_feat,
>>>  	.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_g4x_gfx(struct pci_dev *dev)
>>> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
>>> index 8fff212..0a973c2 100644
>>> --- a/drivers/iommu/intel-svm.c
>>> +++ b/drivers/iommu/intel-svm.c
>>> @@ -227,6 +227,180 @@ static const struct mmu_notifier_ops
>>> intel_mmuops = { 
>>>  static DEFINE_MUTEX(pasid_mutex);
>>>  static LIST_HEAD(global_svm_list);
>>> +#define for_each_svm_dev() \
>>> +	list_for_each_entry(sdev, &svm->devs, list)	\
>>> +	if (dev == sdev->dev)				\
>>> +
>>> +int intel_svm_bind_gpasid(struct iommu_domain *domain,
>>> +			struct device *dev,
>>> +			struct gpasid_bind_data *data)
>>> +{
>>> +	struct intel_iommu *iommu = intel_svm_device_to_iommu(dev);
>>> +	struct intel_svm_dev *sdev;
>>> +	struct intel_svm *svm = NULL;
>>> +	struct dmar_domain *ddomain;
>>> +	int pasid_max;
>>> +	int ret = 0;
>>> +
>>> +	if (WARN_ON(!iommu) || !data)
>>> +		return -EINVAL;
>>> +
>>> +	if (dev_is_pci(dev)) {
>>> +		pasid_max = pci_max_pasids(to_pci_dev(dev));
>>> +		if (pasid_max < 0)
>>> +			return -EINVAL;
>>> +	} else
>>> +		pasid_max = 1 << 20;
>>> +
>>> +	if (data->pasid <= 0 || data->pasid >= pasid_max)
>>> +		return -EINVAL;
>>> +
>>> +	ddomain = to_dmar_domain(domain);
>>> +	/* REVISIT:
>>> +	 * Sanity check adddress width and paging mode support
>>> +	 * width matching in two dimensions:
>>> +	 * 1. paging mode CPU <= IOMMU
>>> +	 * 2. address width Guest <= Host.
>>> +	 */
>>> +	mutex_lock(&pasid_mutex);
>>> +	svm = ioasid_find(NULL, data->pasid, NULL);
>>> +	if (IS_ERR(svm)) {
>>> +		ret = PTR_ERR(svm);
>>> +		goto out;
>>> +	}
>>> +	if (svm) {
>>> +		if (list_empty(&svm->devs)) {
>>> +			dev_err(dev, "GPASID %d has no devices
>>> bond but SVA is allocated\n",
>>> +				data->pasid);
>>> +			ret = -ENODEV; /*
>>> +					* If we found svm for the
>>> PASID, there must be at
>>> +					* least one device bond,
>>> otherwise svm should be freed.
>>> +					*/  
>> comment should be put after list_empty I think. In which circumstances
>> can it happen, I mean, isn't it a BUG_ON case?
> Well, I think failing to bind guest PASID is not severe enough to the
> host to use BUG_ON. It has to be something more catastrophic to use
> BUG_ON right? I will relocate the comments.
When the error is due to a programming error at kernel error (not
induced by any userspace call) I guess it is acceptable to put a BUG_ON.
However the usage of BUG_ON() is generally frown upon so my question
rather was to understand if this can really happen and why?
>>> +			goto out;
>>> +		}
>>> +		for_each_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;
>>> +		}
>>> +	} 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.
>>> +		 */
>>> +		svm->mm = get_task_mm(current);
>>> +		svm->pasid = data->pasid;
>>> +		refcount_set(&svm->refs, 0);
>>> +		ioasid_set_data(data->pasid, svm);
>>> +		INIT_LIST_HEAD_RCU(&svm->devs);
>>> +		INIT_LIST_HEAD(&svm->list);
>>> +
>>> +		mmput(svm->mm);
>>> +	}
>>> +	svm->flags |= SVM_FLAG_GUEST_MODE;
>>> +	sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
>>> +	if (!sdev) {
>>> +		ret = -ENOMEM;  
>> in case of failure what is the state of svm (you added the
>> SVM_FLAG_GUEST_MODE bit typically, is it safe to leave it?)
> The SVM_FLAG_GUEST_MODE flag is used for fault reporting where faults
> such as PRQ need to be injected into the guest. If this kzalloc()
> fails, the nested translation would not be setup for this PASID. So
> there shouldn't be any user of the flag. But I think it is better to
> move svm->flags |= SVM_FLAG_GUEST_MODE; to the end when everything is
> setup for nesting.
ok
> 
>>> +		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);  
>> same here
>>> +		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
>>> +	 */
>>> +	ret = intel_pasid_setup_nested(iommu,
>>> +				dev,
>>> +				(pgd_t *)data->gcr3,
>>> +				data->pasid,
>>> +				data->flags,
>>> +				ddomain,
>>> +				data->addr_width);
>>> +	if (ret) {
>>> +		dev_err(dev, "Failed to set up PASID %d in nested
>>> mode, Err %d\n",
>>> +			data->pasid, ret);
>>> +		kfree(sdev);
>>> +		goto out;
>>> +	}
>>> +
>>> +	init_rcu_head(&sdev->rcu);
>>> +	refcount_inc(&svm->refs);
>>> +	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_svm_dev *sdev;
>>> +	struct intel_iommu *iommu;
>>> +	struct intel_svm *svm;
>>> +	int ret = -EINVAL;
>>> +
>>> +	mutex_lock(&pasid_mutex);
>>> +	iommu = intel_svm_device_to_iommu(dev);
>>> +	if (!iommu)
>>> +		goto out;
>>> +
>>> +	svm = ioasid_find(NULL, pasid, NULL);
>>> +	if (IS_ERR(svm)) {
>>> +		ret = PTR_ERR(svm);
>>> +		goto out;
>>> +	}
>>> +
>>> +	if (!svm)
>>> +		goto out;
>>> +
>>> +	for_each_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 live.
>>> +			 * intel_svm_drain_prq(dev, pasid);
>>> +			 */
>>> +			kfree_rcu(sdev, rcu);
>>> +
>>> +			if (list_empty(&svm->devs)) {
>>> +				list_del(&svm->list);
>>> +				kfree(svm);
>>> +				/*
>>> +				 * We do not free PASID here until
>>> explicit call
>>> +				 * from the guest to free.  
>> can you be confident in the guest?
> No. But I have confident in the kernel VFIO code to manage guest life
> cycle :)
> I assume when a guest doesn't do unbind when it dies or unload a
> assigned device, I expect VFIO to free all the PASIDs. VFIO needs to
> police the PASID ownership anyway in order to make sure a PASID
> assigned to guest A cannot be used to bind from guest B.
> This is the flow I worked out with Yi, who is doing the VFIO part. Any
> particular concerns?
No I just wanted to make sure someone is going to take care of the final
tear down even if the userspace fails to do things as expected. Maybe
adding a comment to explain who has the ownership of the final tear down
would help here.

Thanks

Eric
> 
>>> +				 */
>>> +				ioasid_set_data(pasid, NULL);
>>> +			}
>>> +		}
>>> +		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) {
>>> diff --git a/include/linux/intel-iommu.h
>>> b/include/linux/intel-iommu.h index 48fa164..5d67d0d4 100644
>>> --- a/include/linux/intel-iommu.h
>>> +++ b/include/linux/intel-iommu.h
>>> @@ -677,7 +677,9 @@ int intel_iommu_enable_pasid(struct intel_iommu
>>> *iommu, struct device *dev); int intel_svm_init(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 gpasid_bind_data *data);
>>> +extern int intel_svm_unbind_gpasid(struct device *dev, int pasid);
>>>  struct svm_dev_ops;
>>>  
>>>  struct intel_svm_dev {
>>> @@ -693,12 +695,16 @@ struct intel_svm_dev {
>>>  
>>>  struct intel_svm {
>>>  	struct mmu_notifier notifier;
>>> -	struct mm_struct *mm;
>>> +	union {
>>> +		struct mm_struct *mm;
>>> +		u64 gcr3;
>>> +	};
>>>  	struct intel_iommu *iommu;
>>>  	int flags;
>>>  	int pasid;
>>>  	struct list_head devs;
>>>  	struct list_head list;
>>> +	refcount_t refs; /* # of devs bond to the PASID */  
>> number of devices sharing the same PASID?
> more clear wording, thanks.
>>>  };
>>>  
>>>  extern struct intel_iommu *intel_svm_device_to_iommu(struct device
>>> *dev); diff --git a/include/linux/intel-svm.h
>>> b/include/linux/intel-svm.h index e3f7631..34b0a3b 100644
>>> --- a/include/linux/intel-svm.h
>>> +++ b/include/linux/intel-svm.h
>>> @@ -52,6 +52,13 @@ 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.  
>> binds
> will fix
> 
>>> + * 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)
>>>  
>>>  #ifdef CONFIG_INTEL_IOMMU_SVM
>>>  
>>>   
>>
>> Thanks
>>
>> Eric
> 
> [Jacob Pan]
> 

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