Register an IOMMU fault handler which records faults in
the DMA FAULT region ring buffer. In a subsequent patch, we
will add the signaling of a specific eventfd to allow the
userspace to be notified whenever a new fault as shown up.

Signed-off-by: Eric Auger <eric.au...@redhat.com>

---
v11 -> v12:
- take the fault_queue_lock before reading header (Zenghui)
- also record recoverable errors

v10 -> v11:
- move iommu_unregister_device_fault_handler into
  vfio_pci_disable
- check fault_pages != 0

v8 -> v9:
- handler now takes an iommu_fault handle
- eventfd signaling moved to a subsequent patch
- check the fault type and return an error if != UNRECOV
- still the fault handler registration can fail. We need to
  reach an agreement about how to deal with the situation

v3 -> v4:
- move iommu_unregister_device_fault_handler to vfio_pci_release
---
 drivers/vfio/pci/vfio_pci.c | 45 +++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 7546a81e7fb6..b39d6ed66c71 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -27,6 +27,7 @@
 #include <linux/vgaarb.h>
 #include <linux/nospec.h>
 #include <linux/sched/mm.h>
+#include <linux/circ_buf.h>
 
 #include "vfio_pci_private.h"
 
@@ -335,6 +336,41 @@ static const struct vfio_pci_regops 
vfio_pci_dma_fault_regops = {
        .add_capability = vfio_pci_dma_fault_add_capability,
 };
 
+int vfio_pci_iommu_dev_fault_handler(struct iommu_fault *fault, void *data)
+{
+       struct vfio_pci_device *vdev = (struct vfio_pci_device *)data;
+       struct vfio_region_dma_fault *reg =
+               (struct vfio_region_dma_fault *)vdev->fault_pages;
+       struct iommu_fault *new;
+       u32 head, tail, size;
+       int ret = -EINVAL;
+
+
+       if (WARN_ON(!reg))
+               return ret;
+
+       mutex_lock(&vdev->fault_queue_lock);
+
+       head = reg->head;
+       tail = reg->tail;
+       size = reg->nb_entries;
+
+       new = (struct iommu_fault *)(vdev->fault_pages + reg->offset +
+                                    head * reg->entry_size);
+
+       if (CIRC_SPACE(head, tail, size) < 1) {
+               ret = -ENOSPC;
+               goto unlock;
+       }
+
+       *new = *fault;
+       reg->head = (head + 1) % size;
+       ret = 0;
+unlock:
+       mutex_unlock(&vdev->fault_queue_lock);
+       return ret;
+}
+
 #define DMA_FAULT_RING_LENGTH 512
 
 static int vfio_pci_dma_fault_init(struct vfio_pci_device *vdev)
@@ -376,6 +412,13 @@ static int vfio_pci_dma_fault_init(struct vfio_pci_device 
*vdev)
        header->entry_size = sizeof(struct iommu_fault);
        header->nb_entries = DMA_FAULT_RING_LENGTH;
        header->offset = sizeof(struct vfio_region_dma_fault);
+
+       ret = iommu_register_device_fault_handler(&vdev->pdev->dev,
+                                       vfio_pci_iommu_dev_fault_handler,
+                                       vdev);
+       if (ret) /* the dma fault region is freed in vfio_pci_disable() */
+               goto out;
+
        return 0;
 out:
        kfree(vdev->fault_pages);
@@ -508,6 +551,8 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
                                VFIO_IRQ_SET_ACTION_TRIGGER,
                                vdev->irq_type, 0, 0, NULL);
 
+       WARN_ON(iommu_unregister_device_fault_handler(&vdev->pdev->dev));
+
        /* Device closed, don't need mutex here */
        list_for_each_entry_safe(ioeventfd, ioeventfd_tmp,
                                 &vdev->ioeventfds_list, next) {
-- 
2.21.3

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