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    SubjectRe: [PATCH v2 10/16] iommu: introduce device fault report API
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    Hi Jacob,

    On 06/10/17 00:03, Jacob Pan wrote:
    > Traditionally, device specific faults are detected and handled within
    > their own device drivers. When IOMMU is enabled, faults such as DMA
    > related transactions are detected by IOMMU. There is no generic
    > reporting mechanism to report faults back to the in-kernel device
    > driver or the guest OS in case of assigned devices.
    >
    > Faults detected by IOMMU is based on the transaction's source ID which
    > can be reported at per device basis, regardless of the device type is a
    > PCI device or not.
    >
    > The fault types include recoverable (e.g. page request) and
    > unrecoverable faults(e.g. access error). In most cases, faults can be
    > handled by IOMMU drivers internally. The primary use cases are as
    > follows:
    > 1. page request fault originated from an SVM capable device that is
    > assigned to guest via vIOMMU. In this case, the first level page tables
    > are owned by the guest. Page request must be propagated to the guest to
    > let guest OS fault in the pages then send page response. In this
    > mechanism, the direct receiver of IOMMU fault notification is VFIO,
    > which can relay notification events to QEMU or other user space
    > software.
    >
    > 2. faults need more subtle handling by device drivers. Other than
    > simply invoke reset function, there are needs to let device driver
    > handle the fault with a smaller impact.
    >
    > This patchset is intended to create a generic fault report API such
    > that it can scale as follows:
    > - all IOMMU types
    > - PCI and non-PCI devices
    > - recoverable and unrecoverable faults
    > - VFIO and other other in kernel users
    > - DMA & IRQ remapping (TBD)
    > The original idea was brought up by David Woodhouse and discussions
    > summarized at https://lwn.net/Articles/608914/.
    >
    > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
    > Signed-off-by: Ashok Raj <ashok.raj@intel.com>
    > ---
    [...]
    > +int iommu_register_device_fault_handler(struct device *dev,
    > + iommu_dev_fault_handler_t handler)
    > +{
    > + if (dev->iommu_fault_param)
    > + return -EBUSY;
    > + get_device(dev);
    > + dev->iommu_fault_param =
    > + kzalloc(sizeof(struct iommu_fault_param), GFP_KERNEL);
    > + if (!dev->iommu_fault_param)
    > + return -ENOMEM;
    > + dev->iommu_fault_param->dev_fault_handler = handler;

    Since the handler is owned by a device driver, you also need to clean it
    up when switching the driver (native->VFIO and VFIO->native), in
    iommu_attach_device I suppose.

    Thanks,
    Jean

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