Troubleshooting

This section provides solutions to common problems you may encounter.

Index

• Troubleshooting
  • Index
  • Illegal Instruction Error with SIMD Access in QEMU
    • Problem
    • Solution
  • Could not access KVM kernel module: Permission denied
    • Problem
    • Solution
  • cxl Package Issue
    • Problem
    • Solution
  • daxctl Package Issue
    • Problem
    • Solution
  • xcena_cli Execution Errors
    • Problem
    • Solution
  • Example Test Failures
    • Problem
    • Steps to Troubleshoot

---

Illegal Instruction Error with SIMD Access in QEMU

Problem

When accessing CXL memory allocated by PXL’s memAlloc API using SIMD instructions within QEMU, an illegal instruction error may occur. This issue can also arise when accessing the memory using float* or double* pointers. This is a known issue in QEMU Issue #3075.

Solution

To resolve this issue, run QEMU in no-KVM mode. This can be done by adding the --no-kvm option when starting QEMU:

./run.sh --no-kvm

Note Disabling KVM may reduce guest OS performance.

---

Could not access KVM kernel module: Permission denied

Problem

In order to launch QEMU, this error occurs when the current user lacks the necessary permissions to access the KVM (Kernel-based Virtual Machine) kernel module.

Solution

1. Add User to KVM Group.

   sudo usermod -a -G kvm $USER
   

2. Log out and log back in (or open a new terminal session) to apply the group change.
3. Run QEMU again.

---

cxl Package Issue

Problem

The cxl list command is not working.

Solution

1. Ensure the environment is a Docker container:
2. Check the cxl package version:
   • If the version is incorrect, certain features may not be visible.

     cxl version          # Expected version: 72.1+
     

3. If issues persist, try reinstalling Docker.

---

daxctl Package Issue

Problem

The daxctl list command is not working.

Solution

1. Ensure the environment is a Docker container.
2. Verify that the CXL device is attached as a .Mem device:

   lspci | grep CXL                # Check the BDF (Bus Device Function).
   lspci -vvs <BDF> | grep CXLCtl  # Ensure "Mem+" is included.
   

---

xcena_cli Execution Errors

Problem

The output is 0 in the xcena_cli num-device command.

Solution

1. Ensure the required Python modules are installed:

   pip list | grep -E 'click|pandas|pyvcd|serial|pexpect'
   

2. Check if Docker was started with the --privileged flag:

   ls /sys/fs/cgroup/    # If successful, Docker is running in privileged mode.
   

3. Confirm that the mx_dma module is loaded into the kernel:

   lsmod | grep mx_dma
   

4. (Re-)Install and reload the mx_dma module if necessary:

   docker cp xcena_sdk:/work/driver /tmp/mx_dma
   docker stop xcena_sdk
   docker rm xcena_sdk
   
   cd /tmp/mx_dma
   sudo ./install.sh
   
   reboot
   
   lsmod | grep mx_dma
   
   # If mx_dma is not loaded, reload the modules:
   sudo rmmod cxl_pmem cxl_acpi cxl_pci cxl_core mx_dma
   sudo insmod /lib/modules/5.15.0-43-generic/extra/mx_dma.ko
   sudo insmod /lib/modules/5.15.0-43-generic/extra/cxl_5.15/core/cxl_core.ko
   sudo insmod /lib/modules/5.15.0-43-generic/extra/cxl_5.15/cxl_pci.ko
   sudo insmod /lib/modules/5.15.0-43-generic/extra/cxl_5.15/cxl_acpi.ko
   sudo insmod /lib/modules/5.15.0-43-generic/extra/cxl_5.15/cxl_pmem.ko
   
   # Re-run a Docker container
   

---

Example Test Failures

Problem

An example test fails with a core dump.

Steps to Troubleshoot

1. Check if num_device is greater than or equal to 1:

   xcena_cli num-device
   

   • If num_device is 0, refer to the xcena_cli Execution Errors section.
2. Verify that MSUB bitmap is non-zero:

   xcena_cli device-info 0
   

   • If it is 0x0, offloading cannot proceed.