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    SubjectRe: [PATCH v2 10/16] iommu: introduce device fault report API
    On Fri, 6 Oct 2017 10:36:02 +0100
    Jean-Philippe Brucker <jean-philippe.brucker@arm.com> wrote:

    > 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.
    >
    I was thinking the driver who registered fault handler shall be held
    accountable to unregister. e.g. User must unbind driver (unregister
    fault handler included) before assigning device to vfio-pci. Otherwise,
    VFIO call to register handler would fail.
    I am assuming VFIO needs to have a separate device fault handler of its
    own.

    Jacob

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