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, 125 insertions, 0 deletions

diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S
new file mode 100644
index 000000000..65027e742
--- /dev/null
+++ b/arch/riscv/lib/strcmp.S
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/alternative-macros.h>
+#include <asm/hwcap.h>
+
+/* int strcmp(const char *cs, const char *ct) */
+SYM_FUNC_START(strcmp)
+
+	__ALTERNATIVE_CFG("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB,
+		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))
+
+	/*
+	 * Returns
+	 *   a0 - comparison result, value like strcmp
+	 *
+	 * Parameters
+	 *   a0 - string1
+	 *   a1 - string2
+	 *
+	 * Clobbers
+	 *   t0, t1
+	 */
+1:
+	lbu	t0, 0(a0)
+	lbu	t1, 0(a1)
+	addi	a0, a0, 1
+	addi	a1, a1, 1
+	bne	t0, t1, 2f
+	bnez	t0, 1b
+	li	a0, 0
+	ret
+2:
+	/*
+	 * strcmp only needs to return (< 0, 0, > 0) values
+	 * not necessarily -1, 0, +1
+	 */
+	sub	a0, t0, t1
+	ret
+
+/*
+ * Variant of strcmp using the ZBB extension if available.
+ * The code was published as part of the bitmanip manual
+ * in Appendix A.
+ */
+#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
+strcmp_zbb:
+
+.option push
+.option arch,+zbb
+
+	/*
+	 * Returns
+	 *   a0 - comparison result, value like strcmp
+	 *
+	 * Parameters
+	 *   a0 - string1
+	 *   a1 - string2
+	 *
+	 * Clobbers
+	 *   t0, t1, t2, t3, t4
+	 */
+
+	or	t2, a0, a1
+	li	t4, -1
+	and	t2, t2, SZREG-1
+	bnez	t2, 3f
+
+	/* Main loop for aligned string.  */
+	.p2align 3
+1:
+	REG_L	t0, 0(a0)
+	REG_L	t1, 0(a1)
+	orc.b	t3, t0
+	bne	t3, t4, 2f
+	addi	a0, a0, SZREG
+	addi	a1, a1, SZREG
+	beq	t0, t1, 1b
+
+	/*
+	 * Words don't match, and no null byte in the first
+	 * word. Get bytes in big-endian order and compare.
+	 */
+#ifndef CONFIG_CPU_BIG_ENDIAN
+	rev8	t0, t0
+	rev8	t1, t1
+#endif
+
+	/* Synthesize (t0 >= t1) ? 1 : -1 in a branchless sequence. */
+	sltu	a0, t0, t1
+	neg	a0, a0
+	ori	a0, a0, 1
+	ret
+
+2:
+	/*
+	 * Found a null byte.
+	 * If words don't match, fall back to simple loop.
+	 */
+	bne	t0, t1, 3f
+
+	/* Otherwise, strings are equal. */
+	li	a0, 0
+	ret
+
+	/* Simple loop for misaligned strings. */
+	.p2align 3
+3:
+	lbu	t0, 0(a0)
+	lbu	t1, 0(a1)
+	addi	a0, a0, 1
+	addi	a1, a1, 1
+	bne	t0, t1, 4f
+	bnez	t0, 3b
+
+4:
+	sub	a0, t0, t1
+	ret
+
+.option pop
+#endif
+SYM_FUNC_END(strcmp)
+SYM_FUNC_ALIAS(__pi_strcmp, strcmp)
+EXPORT_SYMBOL(strcmp)