Re: [PATCH v2 10/16] iommu: introduce device fault report API

[Joerg Roedel]

On Thu, Oct 05, 2017 at 04:03:38PM -0700, 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@xxxxxxxxxxxxxxx>
> Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
> ---
>  drivers/iommu/iommu.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/iommu.h | 23 +++++++++++++++++++++
>  2 files changed, 78 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 5a14154..0b058e2 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -554,9 +554,15 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
>  
>  	device->dev = dev;
>  
> +	dev->iommu_fault_param = kzalloc(sizeof(struct iommu_fault_param), GFP_KERNEL);
> +	if (!dev->iommu_fault_param) {
> +		ret = -ENOMEM;
> +		goto err_free_device;
> +	}
> +

This looks like some left-over from a previous version, because
allocation of that structure is done in iommu_register_device_fault_handler()