Re: [PATCH v8 26/29] vfio-pci: Register an iommu fault handler

Alex Williamson
2019-06-03T22:32:05Z

On Sun, 26 May 2019 18:10:01 +0200
Eric Auger <eric.auger@redhat.com> wrote:

> This patch registers a fault handler which records faults in
> a circular buffer and then signals an eventfd. This buffer is
> exposed within the fault region.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v3 -> v4:
> - move iommu_unregister_device_fault_handler to vfio_pci_release
> ---
> drivers/vfio/pci/vfio_pci.c | 49 +++++++++++++++++++++++++++++
> drivers/vfio/pci/vfio_pci_private.h | 1 +
> 2 files changed, 50 insertions(+)
>
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index f75f61127277..520999994ba8 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -30,6 +30,7 @@
> #include <linux/vfio.h>
> #include <linux/vgaarb.h>
> #include <linux/nospec.h>
> +#include <linux/circ_buf.h>
>
> #include "vfio_pci_private.h"
>
> @@ -296,6 +297,46 @@ static const struct vfio_pci_regops vfio_pci_fault_prod_regops = {
> .add_capability = vfio_pci_fault_prod_add_capability,
> };
>
> +int vfio_pci_iommu_dev_fault_handler(struct iommu_fault_event *evt, void *data)
> +{
> + struct vfio_pci_device *vdev = (struct vfio_pci_device *) data;
> + struct vfio_region_fault_prod *prod_region =
> + (struct vfio_region_fault_prod *)vdev->fault_pages;
> + struct vfio_region_fault_cons *cons_region =
> + (struct vfio_region_fault_cons *)(vdev->fault_pages + 2 * PAGE_SIZE);
> + struct iommu_fault *new =
> + (struct iommu_fault *)(vdev->fault_pages + prod_region->offset +
> + prod_region->prod * prod_region->entry_size);
> + int prod, cons, size;
> +
> + mutex_lock(&vdev->fault_queue_lock);
> +
> + if (!vdev->fault_abi)
> + goto unlock;
> +
> + prod = prod_region->prod;
> + cons = cons_region->cons;
> + size = prod_region->nb_entries;
> +
> + if (CIRC_SPACE(prod, cons, size) < 1)
> + goto unlock;
> +
> + *new = evt->fault;
> + prod = (prod + 1) % size;
> + prod_region->prod = prod;
> + mutex_unlock(&vdev->fault_queue_lock);
> +
> + mutex_lock(&vdev->igate);
> + if (vdev->dma_fault_trigger)
> + eventfd_signal(vdev->dma_fault_trigger, 1);
> + mutex_unlock(&vdev->igate);
> + return 0;
> +
> +unlock:
> + mutex_unlock(&vdev->fault_queue_lock);
> + return -EINVAL;
> +}
> +
> static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev)
> {
> struct vfio_region_fault_prod *header;
> @@ -328,6 +369,13 @@ static int vfio_pci_init_fault_region(struct vfio_pci_device *vdev)
> header = (struct vfio_region_fault_prod *)vdev->fault_pages;
> header->version = -1;
> header->offset = PAGE_SIZE;
> +
> + 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);
> @@ -570,6 +618,7 @@ static void vfio_pci_release(void *device_data)
> if (!(--vdev->refcnt)) {
> vfio_spapr_pci_eeh_release(vdev->pdev);
> vfio_pci_disable(vdev);
> + iommu_unregister_device_fault_handler(&vdev->pdev->dev);

But this can fail if there are pending faults which leaves a device
reference and then the system is broken :(

> }
>
> mutex_unlock(&vdev->reflck->lock);
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 8e0a55682d3f..a9276926f008 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -122,6 +122,7 @@ struct vfio_pci_device {
> int ioeventfds_nr;
> struct eventfd_ctx *err_trigger;
> struct eventfd_ctx *req_trigger;
> + struct eventfd_ctx *dma_fault_trigger;
> struct mutex fault_queue_lock;
> int fault_abi;
> struct list_head dummy_resources_list;