[PATCH v3 2/2] vfio: Replace the iommu notifier with a device list

Jason Gunthorpe
2022-07-05T00:59:12Z

Instead of bouncing the function call to the driver op through a blocking
notifier just have the iommu layer call it directly.

Register each device that is being attached to the iommu with the lower
driver which then threads them on a linked list and calls the appropriate
driver op at the right time.

Currently the only use is if dma_unmap() is defined.

Also, fully lock all the debugging tests on the pinning path that a
dma_unmap is registered.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/vfio/vfio.c | 41 ++++---------
drivers/vfio/vfio.h | 12 ++--
drivers/vfio/vfio_iommu_type1.c | 103 ++++++++++++++++++++------------
include/linux/vfio.h | 2 +-
4 files changed, 81 insertions(+), 77 deletions(-)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 610bb884d9197b..e43b9496464bbf 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -231,7 +231,7 @@ int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops)
{
struct vfio_iommu_driver *driver, *tmp;

- if (WARN_ON(!ops->register_notifier != !ops->unregister_notifier))
+ if (WARN_ON(!ops->register_device != !ops->unregister_device))
return -EINVAL;

driver = kzalloc(sizeof(*driver), GFP_KERNEL);
@@ -1080,17 +1080,6 @@ static void vfio_device_unassign_container(struct vfio_device *device)
up_write(&device->group->group_rwsem);
}

-static int vfio_iommu_notifier(struct notifier_block *nb, unsigned long action,
- void *data)
-{
- struct vfio_device *vfio_device =
- container_of(nb, struct vfio_device, iommu_nb);
- struct vfio_iommu_type1_dma_unmap *unmap = data;
-
- vfio_device->ops->dma_unmap(vfio_device, unmap->iova, unmap->size);
- return NOTIFY_OK;
-}
-
static struct file *vfio_device_open(struct vfio_device *device)
{
struct vfio_iommu_driver *iommu_driver;
@@ -1126,15 +1115,9 @@ static struct file *vfio_device_open(struct vfio_device *device)
}

iommu_driver = device->group->container->iommu_driver;
- if (device->ops->dma_unmap && iommu_driver &&
- iommu_driver->ops->register_notifier) {
- unsigned long events = VFIO_IOMMU_NOTIFY_DMA_UNMAP;
-
- device->iommu_nb.notifier_call = vfio_iommu_notifier;
- iommu_driver->ops->register_notifier(
- device->group->container->iommu_data, &events,
- &device->iommu_nb);
- }
+ if (iommu_driver && iommu_driver->ops->register_device)
+ iommu_driver->ops->register_device(
+ device->group->container->iommu_data, device);

up_read(&device->group->group_rwsem);
}
@@ -1174,11 +1157,9 @@ static struct file *vfio_device_open(struct vfio_device *device)
device->ops->close_device(device);

iommu_driver = device->group->container->iommu_driver;
- if (device->ops->dma_unmap && iommu_driver &&
- iommu_driver->ops->unregister_notifier)
- iommu_driver->ops->unregister_notifier(
- device->group->container->iommu_data,
- &device->iommu_nb);
+ if (iommu_driver && iommu_driver->ops->unregister_device)
+ iommu_driver->ops->unregister_device(
+ device->group->container->iommu_data, device);
}
err_undo_count:
device->open_count--;
@@ -1383,11 +1364,9 @@ static int vfio_device_fops_release(struct inode *inode, struct file *filep)
device->ops->close_device(device);

iommu_driver = device->group->container->iommu_driver;
- if (device->ops->dma_unmap && iommu_driver &&
- iommu_driver->ops->unregister_notifier)
- iommu_driver->ops->unregister_notifier(
- device->group->container->iommu_data,
- &device->iommu_nb);
+ if (iommu_driver && iommu_driver->ops->unregister_device)
+ iommu_driver->ops->unregister_device(
+ device->group->container->iommu_data, device);
up_read(&device->group->group_rwsem);
device->open_count--;
if (device->open_count == 0)
diff --git a/drivers/vfio/vfio.h b/drivers/vfio/vfio.h
index 25da02ca1568fc..4a7db1f3c33e7e 100644
--- a/drivers/vfio/vfio.h
+++ b/drivers/vfio/vfio.h
@@ -33,9 +33,6 @@ enum vfio_iommu_notify_type {
VFIO_IOMMU_CONTAINER_CLOSE = 0,
};

-/* events for register_notifier() */
-#define VFIO_IOMMU_NOTIFY_DMA_UNMAP BIT(0)
-
/**
* struct vfio_iommu_driver_ops - VFIO IOMMU driver callbacks
*/
@@ -58,11 +55,10 @@ struct vfio_iommu_driver_ops {
unsigned long *phys_pfn);
int (*unpin_pages)(void *iommu_data,
unsigned long *user_pfn, int npage);
- int (*register_notifier)(void *iommu_data,
- unsigned long *events,
- struct notifier_block *nb);
- int (*unregister_notifier)(void *iommu_data,
- struct notifier_block *nb);
+ void (*register_device)(void *iommu_data,
+ struct vfio_device *vdev);
+ void (*unregister_device)(void *iommu_data,
+ struct vfio_device *vdev);
int (*dma_rw)(void *iommu_data, dma_addr_t user_iova,
void *data, size_t count, bool write);
struct iommu_domain *(*group_iommu_domain)(void *iommu_data,
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index c13b9290e35759..4ddb1f1abd238b 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -67,7 +67,8 @@ struct vfio_iommu {
struct list_head iova_list;
struct mutex lock;
struct rb_root dma_list;
- struct blocking_notifier_head notifier;
+ struct list_head device_list;
+ struct mutex device_list_lock;
unsigned int dma_avail;
unsigned int vaddr_invalid_count;
uint64_t pgsize_bitmap;
@@ -865,8 +866,8 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
}
}

- /* Fail if notifier list is empty */
- if (!iommu->notifier.head) {
+ /* Fail if no dma_umap notifier is registered */
+ if (list_empty(&iommu->device_list)) {
ret = -EINVAL;
goto pin_done;
}
@@ -1287,6 +1288,35 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
return 0;
}

+/*
+ * Notify VFIO drivers using vfio_register_emulated_iommu_dev() to invalidate
+ * and unmap iovas within the range we're about to unmap. Drivers MUST unpin
+ * pages in response to an invalidation.
+ */
+static void vfio_notify_dma_unmap(struct vfio_iommu *iommu,
+ struct vfio_dma *dma)
+{
+ struct vfio_device *device;
+
+ if (list_empty(&iommu->device_list))
+ return;
+
+ /*
+ * The device is expected to call vfio_unpin_pages() for any IOVA it has
+ * pinned within the range. Since vfio_unpin_pages() will eventually
+ * call back down to this code and try to obtain the iommu->lock we must
+ * drop it.
+ */
+ mutex_lock(&iommu->device_list_lock);
+ mutex_unlock(&iommu->lock);
+
+ list_for_each_entry(device, &iommu->device_list, iommu_entry)
+ device->ops->dma_unmap(device, dma->iova, dma->size);
+
+ mutex_unlock(&iommu->device_list_lock);
+ mutex_lock(&iommu->lock);
+}
+
static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
struct vfio_iommu_type1_dma_unmap *unmap,
struct vfio_bitmap *bitmap)
@@ -1406,8 +1436,6 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
}

if (!RB_EMPTY_ROOT(&dma->pfn_list)) {
- struct vfio_iommu_type1_dma_unmap nb_unmap;
-
if (dma_last == dma) {
BUG_ON(++retries > 10);
} else {
@@ -1415,20 +1443,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
retries = 0;
}

- nb_unmap.iova = dma->iova;
- nb_unmap.size = dma->size;
-
- /*
- * Notify anyone (mdev vendor drivers) to invalidate and
- * unmap iovas within the range we're about to unmap.
- * Vendor drivers MUST unpin pages in response to an
- * invalidation.
- */
- mutex_unlock(&iommu->lock);
- blocking_notifier_call_chain(&iommu->notifier,
- VFIO_IOMMU_NOTIFY_DMA_UNMAP,
- &nb_unmap);
- mutex_lock(&iommu->lock);
+ vfio_notify_dma_unmap(iommu, dma);
goto again;
}

@@ -2478,7 +2493,7 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,

if (list_empty(&iommu->emulated_iommu_groups) &&
list_empty(&iommu->domain_list)) {
- WARN_ON(iommu->notifier.head);
+ WARN_ON(!list_empty(&iommu->device_list));
vfio_iommu_unmap_unpin_all(iommu);
}
goto detach_group_done;
@@ -2510,7 +2525,8 @@ static void vfio_iommu_type1_detach_group(void *iommu_data,
if (list_empty(&domain->group_list)) {
if (list_is_singular(&iommu->domain_list)) {
if (list_empty(&iommu->emulated_iommu_groups)) {
- WARN_ON(iommu->notifier.head);
+ WARN_ON(!list_empty(
+ &iommu->device_list));
vfio_iommu_unmap_unpin_all(iommu);
} else {
vfio_iommu_unmap_unpin_reaccount(iommu);
@@ -2571,7 +2587,8 @@ static void *vfio_iommu_type1_open(unsigned long arg)
iommu->dma_avail = dma_entry_limit;
iommu->container_open = true;
mutex_init(&iommu->lock);
- BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
+ mutex_init(&iommu->device_list_lock);
+ INIT_LIST_HEAD(&iommu->device_list);
init_waitqueue_head(&iommu->vaddr_wait);
iommu->pgsize_bitmap = PAGE_MASK;
INIT_LIST_HEAD(&iommu->emulated_iommu_groups);
@@ -3008,28 +3025,40 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
}
}

-static int vfio_iommu_type1_register_notifier(void *iommu_data,
- unsigned long *events,
- struct notifier_block *nb)
+static void vfio_iommu_type1_register_device(void *iommu_data,
+ struct vfio_device *vdev)
{
struct vfio_iommu *iommu = iommu_data;

- /* clear known events */
- *events &= ~VFIO_IOMMU_NOTIFY_DMA_UNMAP;
-
- /* refuse to register if still events remaining */
- if (*events)
- return -EINVAL;
+ if (!vdev->ops->dma_unmap)
+ return;

- return blocking_notifier_chain_register(&iommu->notifier, nb);
+ /*
+ * list_empty(&iommu->device_list) is tested under the iommu->lock while
+ * iteration for dma_unmap must be done under the device_list_lock.
+ * Holding both locks here allows avoiding the device_list_lock in
+ * several fast paths. See vfio_notify_dma_unmap()
+ */
+ mutex_lock(&iommu->lock);
+ mutex_lock(&iommu->device_list_lock);
+ list_add(&vdev->iommu_entry, &iommu->device_list);
+ mutex_unlock(&iommu->device_list_lock);
+ mutex_unlock(&iommu->lock);
}

-static int vfio_iommu_type1_unregister_notifier(void *iommu_data,
- struct notifier_block *nb)
+static void vfio_iommu_type1_unregister_device(void *iommu_data,
+ struct vfio_device *vdev)
{
struct vfio_iommu *iommu = iommu_data;

- return blocking_notifier_chain_unregister(&iommu->notifier, nb);
+ if (!vdev->ops->dma_unmap)
+ return;
+
+ mutex_lock(&iommu->lock);
+ mutex_lock(&iommu->device_list_lock);
+ list_del(&vdev->iommu_entry);
+ mutex_unlock(&iommu->device_list_lock);
+ mutex_unlock(&iommu->lock);
}

static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
@@ -3163,8 +3192,8 @@ static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
.detach_group = vfio_iommu_type1_detach_group,
.pin_pages = vfio_iommu_type1_pin_pages,
.unpin_pages = vfio_iommu_type1_unpin_pages,
- .register_notifier = vfio_iommu_type1_register_notifier,
- .unregister_notifier = vfio_iommu_type1_unregister_notifier,
+ .register_device = vfio_iommu_type1_register_device,
+ .unregister_device = vfio_iommu_type1_unregister_device,
.dma_rw = vfio_iommu_type1_dma_rw,
.group_iommu_domain = vfio_iommu_type1_group_iommu_domain,
.notify = vfio_iommu_type1_notify,
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 8c5c389d42d918..cd76b73f22d64c 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -44,7 +44,7 @@ struct vfio_device {
unsigned int open_count;
struct completion comp;
struct list_head group_next;
- struct notifier_block iommu_nb;
+ struct list_head iommu_entry;
};

/**
--
2.37.0