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

[Zenghui Yu]

Hi Eric,

On 2020/3/21 0:19, Eric Auger wrote:

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>

[...]

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);

Shouldn't 'reg->head' be protected under the fault_queue_lock? Otherwise
things may change behind our backs...

We shouldn't take any assumption about how IOMMU driver would report the
fault (serially or in parallel), I think.

+       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);

Thanks,
Zenghui
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