Why does a kernel panic occur when OpenCL™ Applications are executed on Intel® FPGA Development Kits with IOMMU support enabled?

Description

When executing OpenCL™ host applications on an attached development kit while IOMMU (e.g. intel_iommu) is enabled in a Linux Kernel, a kernel panic may occur and cause the host to hang. 

This may happen even if 'aocl diagnose' and 'aocl program' pass. The hang occurs because the OpenCL™ board support packages (BSPs) for the development kits don't support SR-IOV.

Resolution

To work around this problem, disable IOMMU functionality :

For example on CentOS7.4, with grub2, UEFI and intel_iommu :

1.  Edit /etc/default/grub and delete the following line.
    intel_iommu=on in GRUB_CMDLINE_LINUX

2. Update grub configuration file

     grub2-mkconfig  -o /boot/efi/EFI/centos/grub.cfg

3. Reboot

4. Check /proc/cmdline

    Ensure intel_iommu=on does not appear on the kernel command line.

This workaround does not apply to the Intel FPGA Programmable Acceleration Card (PAC) since that OpenCL™ BSP does support SR-IOV.  If IOMMU is disabled when using the PAC, refer to the Intel® Acceleration Stack Quick Start Guide for instructions to enable the Intel IOMMU driver.