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

Auger Eric
2019-06-04T16:11:47Z

Hi Alex,

On 6/4/19 12:31 AM, Alex Williamson wrote:
> 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 :(
This series only features unrecoverable errors and for those the
unregistration cannot fail. Now unrecoverable errors were added I admit
this is confusing. We need to sort this out or clean the dependencies.

Thanks

Eric
>
>> }
>>
>> 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;
>