Re: [PATCH v3] iommu/s390: Fix race with release_device ops

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On 8/30/22 22:15, Matthew Rosato wrote:
With commit fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev
calls") s390-iommu is supposed to handle dynamic switching between IOMMU
domains and the DMA API handling.  However, this commit does not
sufficiently handle the case where the device is released via a call
to the release_device op as it may occur at the same time as an opposing
attach_dev or detach_dev since the group mutex is not held over
release_device.  This was observed if the device is deconfigured during a
small window during vfio-pci initialization and can result in WARNs and
potential kernel panics.

Handle this by tracking when the device is probed/released via
dev_iommu_priv_set/get().  Ensure that once the device is released only
release_device handles the re-init of the device DMA.

Fixes: fa7e9ecc5e1c ("iommu/s390: Tolerate repeat attach_dev calls")
Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
---
Changes since v2:
- Relocate the list_empty and aperture chekcs in attach_dev to the
   their original locations so they are all done under a single
   acquisition of the spinlock (Heiko)
---
  arch/s390/include/asm/pci.h |  1 +
  arch/s390/pci/pci.c         |  1 +
  drivers/iommu/s390-iommu.c  | 39 ++++++++++++++++++++++++++++++++++---
  3 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
index 7b4cdadbc023..080251e7b275 100644
--- a/arch/s390/include/asm/pci.h
+++ b/arch/s390/include/asm/pci.h
@@ -157,6 +157,7 @@ struct zpci_dev {
  	/* DMA stuff */
  	unsigned long	*dma_table;
  	spinlock_t	dma_table_lock;
+	struct mutex	dma_domain_lock; /* protects s390_domain value */
  	int		tlb_refresh;
spinlock_t iommu_bitmap_lock;
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 73cdc5539384..973edd32ecc9 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -832,6 +832,7 @@ struct zpci_dev *zpci_create_device(u32 fid, u32 fh, enum zpci_state state)
  	kref_init(&zdev->kref);
  	mutex_init(&zdev->lock);
  	mutex_init(&zdev->kzdev_lock);
+	mutex_init(&zdev->dma_domain_lock);
rc = zpci_init_iommu(zdev);
  	if (rc)
diff --git a/drivers/iommu/s390-iommu.c b/drivers/iommu/s390-iommu.c
index c898bcbbce11..1137d669e849 100644
--- a/drivers/iommu/s390-iommu.c
+++ b/drivers/iommu/s390-iommu.c
@@ -99,6 +99,14 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
  	if (!domain_device)
  		return -ENOMEM;
+ /* Leave now if the device has already been released */
+	mutex_lock(&zdev->dma_domain_lock);
+	if (!dev_iommu_priv_get(dev)) {
+		mutex_unlock(&zdev->dma_domain_lock);
+		kfree(domain_device);
+		return 0;
+	}
+
  	if (zdev->dma_table && !zdev->s390_domain) {
  		cc = zpci_dma_exit_device(zdev);
  		if (cc) {
@@ -132,9 +140,10 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
  		goto out_restore;
  	}
  	domain_device->zdev = zdev;
-	zdev->s390_domain = s390_domain;
  	list_add(&domain_device->list, &s390_domain->devices);
  	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
+	zdev->s390_domain = s390_domain;
+	mutex_unlock(&zdev->dma_domain_lock);
return 0; @@ -147,6 +156,7 @@ static int s390_iommu_attach_device(struct iommu_domain *domain,
  				   virt_to_phys(zdev->dma_table));
  	}
  out_free:
+	mutex_unlock(&zdev->dma_domain_lock);
  	kfree(domain_device);
return rc;
@@ -176,17 +186,22 @@ static void s390_iommu_detach_device(struct iommu_domain *domain,
  	}
  	spin_unlock_irqrestore(&s390_domain->list_lock, flags);
- if (found && (zdev->s390_domain == s390_domain)) {
+	mutex_lock(&zdev->dma_domain_lock);
+	if (found && (zdev->s390_domain == s390_domain) &&
+	    dev_iommu_priv_get(dev)) {
  		zdev->s390_domain = NULL;
  		zpci_unregister_ioat(zdev, 0);
  		zpci_dma_init_device(zdev);
  	}
+	mutex_unlock(&zdev->dma_domain_lock);
  }
static struct iommu_device *s390_iommu_probe_device(struct device *dev)
  {
  	struct zpci_dev *zdev = to_zpci_dev(dev);
+ dev_iommu_priv_set(dev, zdev);
+
  	return &zdev->iommu_dev;
  }
@@ -206,10 +221,28 @@ static void s390_iommu_release_device(struct device *dev)
  	 *
  	 * So let's call detach_dev from here if it hasn't been called before.
  	 */
-	if (zdev && zdev->s390_domain) {
+	if (zdev) {
+		/*
+		 * Clear priv to block further attaches for this device,
+		 * ensure detaches don't init DMA.  Hold the domain lock
+		 * to ensure that attach/detach get a consistent view of
+		 * whether or not the device is released.
+		 */
+		mutex_lock(&zdev->dma_domain_lock);
+		dev_iommu_priv_set(dev, NULL);
+		mutex_unlock(&zdev->dma_domain_lock);
+		/* Make sure this device is removed from the domain list */
  		domain = iommu_get_domain_for_dev(dev);

Shouldn't you take the group_mutex before calling directly s390_iommu_detach_device from here?

  		if (domain)
  			s390_iommu_detach_device(domain, dev);



+		/* Now ensure DMA is initialized from here */
+		mutex_lock(&zdev->dma_domain_lock);
+		if (zdev->s390_domain) {
+			zdev->s390_domain = NULL;
+			zpci_unregister_ioat(zdev, 0);
+			zpci_dma_init_device(zdev);
+		}
+		mutex_unlock(&zdev->dma_domain_lock);
  	}
  }
--
Pierre Morel
IBM Lab Boeblingen



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