[PATCH v3 0/8] Introduce debugfs support in IOMMU

Dheeraj Kumar Srivastava
2025-02-06T06:00:26Z

From: root <root@BLRDHSRIVAS.amd.com>

Introducing debugfs support in AMD/IOMMU driver that will allow
userspace to dump below IOMMU information
1) MMIO and Capability register per IOMMU
2) Command buffer
3) Device table entry
4) Interrupt remapping table entry

Analyzing contents of IOMMU data structures helps in understanding IOMMU
capabilities and behavior and debug issues faster.

1. MMIO and Capability registers - Add support to dump MMIO and Capability
registers per IOMMU.

Example:
a. Write MMIO register offset to dump it
$ echo 0x18 > /sys/kernel/debug/iommu/amd/iommu00/mmio
$ cat /sys/kernel/debug/iommu/amd/iommu00/mmio

Output:
$ 0x0003f48d

b. Write capability register offset to dump it
$ echo 0x10 > /sys/kernel/debug/iommu/amd/iommu00/capability
$ cat /sys/kernel/debug/iommu/amd/iommu00/capability

Output:
$ 0x00203040

2. Command buffer - Add support to dump per IOMMU command buffer.

Example:
a. cat /sys/kernel/debug/iommu/amd/iommu00/cmdbuf

Output:
CMD Buffer Head Offset:339 Tail Offset:339
0: 00835001100000010000990000000000
1: 0000000030000005fffff0037fffffff
2: 00835001100000010000990100000000
3: 0000000030000005fffff0037fffffff
4: 00835001100000010000990200000000
...................................
...................................
...................................

3. Device table - Add support to dump device table per IOMMU.

Example:
a. Write device id to dump device table entry for that device
$ echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid
$ cat /sys/kernel/debug/iommu/amd/devid

Output:
0000:01:00.0

Dump the device table entry for the input given
$ cat /sys/kernel/debug/iommu/amd/devtbl

Output:
DeviceId QWORD[3] QWORD[2] QWORD[1] QWORD[0] iommu
0000:01:00.0 0000000000000000 20000001373b8013 0000000000000038 6000000114d7b603 iommu3

b. Write device id to dump device table entry for that device
$ echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid
$ cat /sys/kernel/debug/iommu/amd/devid

Output:
0000:01:00.0

Dump the device table entry for the input given
$ cat /sys/kernel/debug/iommu/amd/devtbl

Output:
DeviceId QWORD[3] QWORD[2] QWORD[1] QWORD[0] iommu
0000:01:00.0 0000000000000000 20000001373b8013 0000000000000038 6000000114d7b603 iommu3

4. Interrupt remapping table - Add support to dump IRT table valid entries in
"iommu_irqtbl" file. This supports user input to dump IRT entry for a
specific pci device.

Example:
a. Write device id to dump device table entry for that device
$ echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid
$ cat /sys/kernel/debug/iommu/amd/devid

Output:
0000:01:00.0

Dump the device table entry for the input given
$ cat /sys/kernel/debug/iommu/amd/irtbl

Output:
DeviceId 0000:01:00.0
IRT[0000] 00000000000000200000000000000241
IRT[0001] 00000000000000200000000000000841
IRT[0002] 00000000000000200000000000002041
IRT[0003] 00000000000000200000000000008041
IRT[0004] 00000000000000200000000000020041
..........................................
..........................................
..........................................

b. Write device id to dump device table entry for that device
$ echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid
$ cat /sys/kernel/debug/iommu/amd/devid

Output:
0000:01:00.0

Dump the device table entry for the input given
$ cat /sys/kernel/debug/iommu/amd/irttbl

Output:
Device 0000:01:00.0
IRT[0000] 00000000000000200000000000000241
IRT[0001] 00000000000000200000000000000841
IRT[0002] 00000000000000200000000000002041
IRT[0003] 00000000000000200000000000008041
IRT[0004] 00000000000000200000000000020041
..........................................
..........................................
..........................................

Open question:[Suggestion from Bjorn Helgaas] Instead of using device-id input with
"/sys/kernel/debug/iommu/amd/devid", can we have something like other drivers
have "/sys/kernel/debug/iommu/amd/<bdf>/".

Each "/sys/kernel/debug/iommu/amd/<bdf>/" will have "devtbl" and "irqtbl" files
for device table and interrupt remapping table dump file.

Changes since v2:
-> Patch 2/8 and 3/8: Use single file mmio and capability for input and output registers
offset and registers dump respctively.
-> Patch 8/8: Correct path for files "irqtbl" and "devtbl" in Documentation

Changes since v1:
-> Patch 2/8 and 3/8: Use kstrtou32_from_user() instead of memdup_user_nul() --> kstrtou32()
-> Patch 4/8: Dump command buffer head and tail offset instead of head and tail pointer registers.
-> Patch 8/8: Fix bot reported warning on v1 upstream.

Dheeraj Kumar Srivastava (8):
iommu/amd: Refactor AMD IOMMU debugfs initial setup
iommu/amd: Add debugfs support to dump IOMMU MMIO registers
iommu/amd: Add debugfs support to dump IOMMU Capability registers
iommu/amd: Add debugfs support to dump IOMMU command buffer
iommu/amd: Add support for device id user input
iommu/amd: Add debugfs support to dump device table
iommu/amd: Add debugfs support to dump IRT Table
iommu/amd: Add documentation for AMD IOMMU debugfs support

Documentation/ABI/testing/debugfs-amd-iommu | 114 +++++++
drivers/iommu/amd/amd_iommu.h | 4 +-
drivers/iommu/amd/amd_iommu_types.h | 7 +
drivers/iommu/amd/debugfs.c | 350 +++++++++++++++++++-
drivers/iommu/amd/init.c | 5 +-
drivers/iommu/amd/iommu.c | 7 -
6 files changed, 466 insertions(+), 21 deletions(-)
create mode 100644 Documentation/ABI/testing/debugfs-amd-iommu

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2.25.1