x86/amd_node: Fix PCI device reference counting in amd_smn_init()grafted

The local "root" pointer is a temporary variable used during the device
search. Therefore, refcount related to the search iterators should be cleaned
up after the search is complete.

Use the __free() cleanup macro to ensure the refcount is decremented when the
temporary pointer goes out of scope.

Additionally, increment the refcount when caching a root pointer. This ensures
the in-use refcount is separate from the temporary search refcounting.

Finally, drop the redundant "root = NULL" before the second search loop. The
pci_get_class() iterator always decrements the refcount of its "from"
argument, so the first loop can only fall through with "root" already NULL.

Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching")
Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com
Reported-by: Sashiko <sashiko-bot@kernel.org>
Assisted-by: LLM
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Cc: <stable@kernel.org>
Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com

1 files changed, 131 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-amd-iommu b/Documentation/ABI/testing/debugfs-amd-iommu
new file mode 100644
index 000000000..5621a66aa
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-amd-iommu
@@ -0,0 +1,131 @@
+What:		/sys/kernel/debug/iommu/amd/iommu<x>/mmio
+Date:		January 2025
+Contact:	Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
+Description:
+		This file provides read/write access for user input. Users specify the
+		MMIO register offset for iommu<x>, and the file outputs the corresponding
+		MMIO register value of iommu<x>
+
+		Example::
+
+		  $ echo "0x18" > /sys/kernel/debug/iommu/amd/iommu00/mmio
+		  $ cat /sys/kernel/debug/iommu/amd/iommu00/mmio
+
+		Output::
+
+		  Offset:0x18 Value:0x000c22000003f48d
+
+What:		/sys/kernel/debug/iommu/amd/iommu<x>/capability
+Date:		January 2025
+Contact:	Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
+Description:
+		This file provides read/write access for user input. Users specify the
+		capability register offset for iommu<x>, and the file outputs the
+		corresponding capability register value of iommu<x>.
+
+		Example::
+
+		  $ echo "0x10" > /sys/kernel/debug/iommu/amd/iommu00/capability
+		  $ cat /sys/kernel/debug/iommu/amd/iommu00/capability
+
+		Output::
+
+		  Offset:0x10 Value:0x00203040
+
+What:		/sys/kernel/debug/iommu/amd/iommu<x>/cmdbuf
+Date:		January 2025
+Contact:	Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
+Description:
+		This file is a read-only output file containing iommu<x> command
+		buffer entries.
+
+		Examples::
+
+		  $ cat /sys/kernel/debug/iommu/amd/iommu<x>/cmdbuf
+
+		Output::
+
+		  CMD Buffer Head Offset:339 Tail Offset:339
+		    0: 00835001 10000001 00003c00 00000000
+		    1: 00000000 30000005 fffff003 7fffffff
+		    2: 00835001 10000001 00003c01 00000000
+		    3: 00000000 30000005 fffff003 7fffffff
+		    4: 00835001 10000001 00003c02 00000000
+		    5: 00000000 30000005 fffff003 7fffffff
+		    6: 00835001 10000001 00003c03 00000000
+		    7: 00000000 30000005 fffff003 7fffffff
+		    8: 00835001 10000001 00003c04 00000000
+		    9: 00000000 30000005 fffff003 7fffffff
+		   10: 00835001 10000001 00003c05 00000000
+		   11: 00000000 30000005 fffff003 7fffffff
+		  [...]
+
+What:		/sys/kernel/debug/iommu/amd/devid
+Date:		January 2025
+Contact:	Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
+Description:
+		This file provides read/write access for user input. Users specify the
+		device ID, which can be used to dump IOMMU data structures such as the
+		interrupt remapping table and device table.
+
+		Example:
+
+		1.
+		  ::
+
+		    $ echo 0000:01:00.0 > /sys/kernel/debug/iommu/amd/devid
+		    $ cat /sys/kernel/debug/iommu/amd/devid
+
+		  Output::
+
+		    0000:01:00.0
+
+		2.
+		  ::
+
+		    $ echo 01:00.0 > /sys/kernel/debug/iommu/amd/devid
+		    $ cat /sys/kernel/debug/iommu/amd/devid
+
+		  Output::
+
+		    0000:01:00.0
+
+What:		/sys/kernel/debug/iommu/amd/devtbl
+Date:		January 2025
+Contact:	Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
+Description:
+		This file is a read-only output file containing the device table entry
+		for the device ID provided in /sys/kernel/debug/iommu/amd/devid.
+
+		Example::
+
+		  $ 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
+
+What:		/sys/kernel/debug/iommu/amd/irqtbl
+Date:		January 2025
+Contact:	Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
+Description:
+		This file is a read-only output file containing valid IRT table entries
+		for the device ID provided in /sys/kernel/debug/iommu/amd/devid.
+
+		Example::
+
+		  $ cat /sys/kernel/debug/iommu/amd/irqtbl
+
+		Output::
+
+		  DeviceId 0000:01:00.0
+		  IRT[0000] 0000000000000020 0000000000000241
+		  IRT[0001] 0000000000000020 0000000000000841
+		  IRT[0002] 0000000000000020 0000000000002041
+		  IRT[0003] 0000000000000020 0000000000008041
+		  IRT[0004] 0000000000000020 0000000000020041
+		  IRT[0005] 0000000000000020 0000000000080041
+		  IRT[0006] 0000000000000020 0000000000200041
+		  IRT[0007] 0000000000000020 0000000000800041
+		  [...]