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Date:   Mon, 28 Oct 2019 15:29:45 -0700
From:   Jacob Pan <jacob.jun.pan@linux.intel.com>
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>,
        Yi Liu <yi.l.liu@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jonathan Cameron <jic23@kernel.org>,
        Eric Auger <eric.auger@redhat.com>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH v7 09/11] iommu/vt-d: Add bind guest PASID support
Message-ID: <20191028152945.13bc22fa@jacob-builder>
In-Reply-To: <a9a1c3ed-0134-f531-fbf1-789f6cc78ce3@linux.intel.com>
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        <1571946904-86776-10-git-send-email-jacob.jun.pan@linux.intel.com>
        <a9a1c3ed-0134-f531-fbf1-789f6cc78ce3@linux.intel.com>
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Hi Baolu,

Appreciate the thorough review, comments inline.

On Sat, 26 Oct 2019 10:01:19 +0800
Lu Baolu <baolu.lu@linux.intel.com> wrote:

> Hi,
> 
> On 10/25/19 3:55 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@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   | 184
> > ++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/intel-iommu.h |   8 +- include/linux/intel-svm.h   |
> > 17 ++++ 4 files changed, 212 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index acd1ac787d8b..5fab32fbc4b4
> > 100644 --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -6026,6 +6026,10 @@ 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 a18b02a9709d..ae13a310cf96 100644
> > --- a/drivers/iommu/intel-svm.c
> > +++ b/drivers/iommu/intel-svm.c
> > @@ -216,6 +216,190 @@ static LIST_HEAD(global_svm_list);
> >   	list_for_each_entry(sdev, &svm->devs, list)	\
> >   	if (dev == sdev->dev)				\  
> 
> Add an indent tab please.
> 
looks good.
> >   
> > +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;
> > +	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)  
> 
> Alignment should match open parenthesis.
> 
> Run "scripts/checkpatch.pl --strict" for all in this patch. I will
> ignore others.
> 
it was my editor's setting :), will do.

> > +		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;
> > +	}
> > +
> > +	/*
> > +	 * 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);
> > +	/* REVISIT:
> > +	 * Sanity check adddress width and paging mode support  
> 
> s/adddress/address/g
> 
good catch, I will add the check for paging mode and this comment is no
longer needed.
> > +	 * width matching in two dimensions:
> > +	 * 1. paging mode CPU <= IOMMU
> > +	 * 2. address width Guest <= Host.
> > +	 */ > +	mutex_lock(&pasid_mutex);
> > +	svm = ioasid_find(NULL, data->hpasid, NULL);
> > +	if (IS_ERR(svm)) {
> > +		ret = PTR_ERR(svm);
> > +		goto out;
> > +	}  
> 
> A blank line looks better.
> 
true.
> > +	if (svm) {
> > +		/*
> > +		 * If we found svm for the PASID, there must be at
> > +		 * least one device bond, otherwise svm should be
> > freed.
> > +		 */
> > +		BUG_ON(list_empty(&svm->devs));  
> 
> Avoid crashing kernel, use WARN_ON() instead.
> 
> 	if (WARN_ON(list_empty(&svm->devs))) {
> 		ret = -EINVAL;
> 		goto out;
> 	}
> 
Yeah, WARN_ON is better, should let the kernel continue for easy debug.
Though this is an indication of serious problem.
> > +
> > +		for_each_svm_dev(svm, dev) {
> > +			/* In case of multiple sub-devices of the
> > same pdev assigned, we should  
> 
> Make line shorter. Not over 80 characters.
> 
> The same for other lines.
> 
sure.
> > +			 * allow multiple bind calls with the same
> > PASID and pdev.
> > +			 */
> > +			sdev->users++;
> > +			goto out;
> > +		}  
> 
> I remember I ever pointed this out before. But I forgot how we
> addressed it. So forgive me if this has been addressed.
> 
> What if we have a valid bound svm but @dev doesn't belong to it
> (a.k.a. @dev not in svm->devs list)?
> 
If we are binding a new device to an existing/active PASID, the code
will allocate a new sdev and add that to the svm->devs list.
> > +	} 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->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);
> > +		INIT_LIST_HEAD(&svm->list);
> > +
> > +		mmput(svm->mm);
> > +	}  
> 
> A blank line, please.
looks good.
> 
> > +	sdev = kzalloc(sizeof(*sdev), GFP_KERNEL);
> > +	if (!sdev) {
> > +		if (list_empty(&svm->devs))
> > +			kfree(svm);  
> 
> This is dangerous. This might leave a wild pointer bound with gpasid.
> 
why is that? can you please explain?
if the list is empty that means we just allocated the new svm, no
users. why can't we free it here?

> > +		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);
> > +		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->gpgd,
> > +				data->hpasid,
> > +				&data->vtd,
> > +				ddomain,
> > +				data->addr_width);
> > +	if (ret) {
> > +		dev_err(dev, "Failed to set up PASID %llu in
> > nested mode, Err %d\n",
> > +			data->hpasid, ret);  
> 
> This error handling is insufficient. You should at least:
> 
> 1. free sdev
already done below

> 2. if list_empty(&svm->devs)
> 	unbound the svm from gpasid
> 	free svm
> 
yes, agreed.

> The same for above error handling. Add a branch for error recovery at
> the end of function might help here.
> 
not sure which code is the same as above? could you point it out?
> > +		kfree(sdev);
> > +		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_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;  
> 
> Make it symmetrical with bind function.
> 
> 	if (WARN_ON(!iommu))
> 		goto out;
> 
sounds good.
> > +
> > +	svm = ioasid_find(NULL, pasid, NULL);
> > +	if (IS_ERR_OR_NULL(svm)) {
> > +		ret = PTR_ERR(svm);  
> 
> If svm == NULL, this function will return success. This is not
> expected, right?
> 
good catch, will fix.
> > +		goto out;
> > +	}
> > +
> > +	for_each_svm_dev(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)) {
> > +				list_del(&svm->list);
> > +				kfree(svm);
> > +				/*
> > +				 * 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.
> > +				 */
> > +				ioasid_set_data(pasid, NULL);  
> 
> Exchange order. First unbind svm from gpasid and then free svm.
> 
I am not following, aren't we already doing free svm after unbind?
please explain.
> > +			}
> > +		}
> > +		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
> > 3dba6ad3e9ad..6c74c71b1ebf 100644 --- a/include/linux/intel-iommu.h
> > +++ b/include/linux/intel-iommu.h
> > @@ -673,7 +673,9 @@ 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 iommu_gpasid_bind_data
> > *data); +extern int intel_svm_unbind_gpasid(struct device *dev, int
> > pasid); struct svm_dev_ops;
> >   
> >   struct intel_svm_dev {
> > @@ -690,9 +692,13 @@ 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.
> > +		     */
> >   	struct list_head devs;
> >   	struct list_head list;
> >   };
> > diff --git a/include/linux/intel-svm.h b/include/linux/intel-svm.h
> > index 94f047a8a845..a2c189ad0b01 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)  
> 
> How about keeping this aligned with top by adding a tab?
> 
sounds good.
> BIT macro is preferred. Hence, make it BIT(1), BIT(2), BIT(3) is
> preferred.
> 
I know, but the existing mainline code is not using BIT, so I wanted
to keep coding style consistent. Perhaps a separate cleanup patch will
do later.
> > +/*
> > + * 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)  
> 
> Ditto.
> 
> Best regards,
> baolu

[Jacob Pan]