[PATCH v10 05/11] vfio/pci: Register an iommu fault handler

[Eric Auger]

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>

---

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 | 42 +++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 586b89debed5..69595c240baf 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -27,6 +27,7 @@
 #include <linux/vfio.h>
 #include <linux/vgaarb.h>
 #include <linux/nospec.h>
+#include <linux/circ_buf.h>
 
 #include "vfio_pci_private.h"
 
@@ -283,6 +284,38 @@ 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 =
+               (struct iommu_fault *)(vdev->fault_pages + reg->offset +
+                       reg->head * reg->entry_size);
+       int head, tail, size;
+       int ret = 0;
+
+       if (fault->type != IOMMU_FAULT_DMA_UNRECOV)
+               return -ENOENT;
+
+       mutex_lock(&vdev->fault_queue_lock);
+
+       head = reg->head;
+       tail = reg->tail;
+       size = reg->nb_entries;
+
+       if (CIRC_SPACE(head, tail, size) < 1) {
+               ret = -ENOSPC;
+               goto unlock;
+       }
+
+       *new = *fault;
+       reg->head = (head + 1) % size;
+unlock:
+       mutex_unlock(&vdev->fault_queue_lock);
+       return ret;
+}
+
 #define DMA_FAULT_RING_LENGTH 512
 
 static int vfio_pci_init_dma_fault_region(struct vfio_pci_device *vdev)
@@ -317,6 +350,13 @@ static int vfio_pci_init_dma_fault_region(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)
+               goto out;
+
        return 0;
 out:
        kfree(vdev->fault_pages);
@@ -542,6 +582,8 @@ static void vfio_pci_release(void *device_data)
        if (!(--vdev->refcnt)) {
                vfio_spapr_pci_eeh_release(vdev->pdev);
                vfio_pci_disable(vdev);
+               /* TODO: Failure problematics */
+               iommu_unregister_device_fault_handler(&vdev->pdev->dev);
        }
 
        mutex_unlock(&vdev->reflck->lock);
-- 
2.20.1

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