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, 235 insertions, 0 deletions

diff --git a/arch/x86/lib/cmdline.c b/arch/x86/lib/cmdline.c
new file mode 100644
index 000000000..c65cd5550
--- /dev/null
+++ b/arch/x86/lib/cmdline.c
@@ -0,0 +1,235 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Misc librarized functions for cmdline poking.
+ */
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/ctype.h>
+
+#include <asm/setup.h>
+#include <asm/cmdline.h>
+#include <asm/bug.h>
+
+static inline int myisspace(u8 c)
+{
+	return c <= ' ';	/* Close enough approximation */
+}
+
+/*
+ * Find a boolean option (like quiet,noapic,nosmp....)
+ *
+ * @cmdline: the cmdline string
+ * @max_cmdline_size: the maximum size of cmdline
+ * @option: option string to look for
+ *
+ * Returns the position of that @option (starts counting with 1)
+ * or 0 on not found.  @option will only be found if it is found
+ * as an entire word in @cmdline.  For instance, if @option="car"
+ * then a cmdline which contains "cart" will not match.
+ */
+static int
+__cmdline_find_option_bool(const char *cmdline, int max_cmdline_size,
+			   const char *option)
+{
+	char c;
+	int pos = 0, wstart = 0;
+	const char *opptr = NULL;
+	enum {
+		st_wordstart = 0,	/* Start of word/after whitespace */
+		st_wordcmp,	/* Comparing this word */
+		st_wordskip,	/* Miscompare, skip */
+	} state = st_wordstart;
+
+	if (!cmdline)
+		return -1;      /* No command line */
+
+	/*
+	 * This 'pos' check ensures we do not overrun
+	 * a non-NULL-terminated 'cmdline'
+	 */
+	while (pos < max_cmdline_size) {
+		c = *(char *)cmdline++;
+		pos++;
+
+		switch (state) {
+		case st_wordstart:
+			if (!c)
+				return 0;
+			else if (myisspace(c))
+				break;
+
+			state = st_wordcmp;
+			opptr = option;
+			wstart = pos;
+			fallthrough;
+
+		case st_wordcmp:
+			if (!*opptr) {
+				/*
+				 * We matched all the way to the end of the
+				 * option we were looking for.  If the
+				 * command-line has a space _or_ ends, then
+				 * we matched!
+				 */
+				if (!c || myisspace(c))
+					return wstart;
+				/*
+				 * We hit the end of the option, but _not_
+				 * the end of a word on the cmdline.  Not
+				 * a match.
+				 */
+			} else if (!c) {
+				/*
+				 * Hit the NULL terminator on the end of
+				 * cmdline.
+				 */
+				return 0;
+			} else if (c == *opptr++) {
+				/*
+				 * We are currently matching, so continue
+				 * to the next character on the cmdline.
+				 */
+				break;
+			}
+			state = st_wordskip;
+			fallthrough;
+
+		case st_wordskip:
+			if (!c)
+				return 0;
+			else if (myisspace(c))
+				state = st_wordstart;
+			break;
+		}
+	}
+
+	return 0;	/* Buffer overrun */
+}
+
+/*
+ * Find a non-boolean option (i.e. option=argument). In accordance with
+ * standard Linux practice, if this option is repeated, this returns the
+ * last instance on the command line.
+ *
+ * @cmdline: the cmdline string
+ * @max_cmdline_size: the maximum size of cmdline
+ * @option: option string to look for
+ * @buffer: memory buffer to return the option argument
+ * @bufsize: size of the supplied memory buffer
+ *
+ * Returns the length of the argument (regardless of if it was
+ * truncated to fit in the buffer), or -1 on not found.
+ */
+static int
+__cmdline_find_option(const char *cmdline, int max_cmdline_size,
+		      const char *option, char *buffer, int bufsize)
+{
+	char c;
+	int pos = 0, len = -1;
+	const char *opptr = NULL;
+	char *bufptr = buffer;
+	enum {
+		st_wordstart = 0,	/* Start of word/after whitespace */
+		st_wordcmp,	/* Comparing this word */
+		st_wordskip,	/* Miscompare, skip */
+		st_bufcpy,	/* Copying this to buffer */
+	} state = st_wordstart;
+
+	if (!cmdline)
+		return -1;      /* No command line */
+
+	/*
+	 * This 'pos' check ensures we do not overrun
+	 * a non-NULL-terminated 'cmdline'
+	 */
+	while (pos++ < max_cmdline_size) {
+		c = *(char *)cmdline++;
+		if (!c)
+			break;
+
+		switch (state) {
+		case st_wordstart:
+			if (myisspace(c))
+				break;
+
+			state = st_wordcmp;
+			opptr = option;
+			fallthrough;
+
+		case st_wordcmp:
+			if ((c == '=') && !*opptr) {
+				/*
+				 * We matched all the way to the end of the
+				 * option we were looking for, prepare to
+				 * copy the argument.
+				 */
+				len = 0;
+				bufptr = buffer;
+				state = st_bufcpy;
+				break;
+			} else if (c == *opptr++) {
+				/*
+				 * We are currently matching, so continue
+				 * to the next character on the cmdline.
+				 */
+				break;
+			}
+			state = st_wordskip;
+			fallthrough;
+
+		case st_wordskip:
+			if (myisspace(c))
+				state = st_wordstart;
+			break;
+
+		case st_bufcpy:
+			if (myisspace(c)) {
+				state = st_wordstart;
+			} else {
+				/*
+				 * Increment len, but don't overrun the
+				 * supplied buffer and leave room for the
+				 * NULL terminator.
+				 */
+				if (++len < bufsize)
+					*bufptr++ = c;
+			}
+			break;
+		}
+	}
+
+	if (bufsize)
+		*bufptr = '\0';
+
+	return len;
+}
+
+int cmdline_find_option_bool(const char *cmdline, const char *option)
+{
+	int ret;
+
+	ret = __cmdline_find_option_bool(cmdline, COMMAND_LINE_SIZE, option);
+	if (ret > 0)
+		return ret;
+
+	if (IS_ENABLED(CONFIG_CMDLINE_BOOL) && !builtin_cmdline_added)
+		return __cmdline_find_option_bool(builtin_cmdline, COMMAND_LINE_SIZE, option);
+
+	return ret;
+}
+
+int cmdline_find_option(const char *cmdline, const char *option, char *buffer,
+			int bufsize)
+{
+	int ret;
+
+	ret = __cmdline_find_option(cmdline, COMMAND_LINE_SIZE, option, buffer, bufsize);
+	if (ret > 0)
+		return ret;
+
+	if (IS_ENABLED(CONFIG_CMDLINE_BOOL) && !builtin_cmdline_added)
+		return __cmdline_find_option(builtin_cmdline, COMMAND_LINE_SIZE, option, buffer, bufsize);
+
+	return ret;
+}