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, 59 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/cpu.h b/drivers/md/dm-vdo/cpu.h
new file mode 100644
index 000000000..d6a2615ba
--- /dev/null
+++ b/drivers/md/dm-vdo/cpu.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef UDS_CPU_H
+#define UDS_CPU_H
+
+#include <linux/cache.h>
+
+/**
+ * uds_prefetch_address() - Minimize cache-miss latency by attempting to move data into a CPU cache
+ *                          before it is accessed.
+ *
+ * @address: the address to fetch (may be invalid)
+ * @for_write: must be constant at compile time--false if for reading, true if for writing
+ */
+static inline void uds_prefetch_address(const void *address, bool for_write)
+{
+	/*
+	 * for_write won't be a constant if we are compiled with optimization turned off, in which
+	 * case prefetching really doesn't matter. clang can't figure out that if for_write is a
+	 * constant, it can be passed as the second, mandatorily constant argument to prefetch(),
+	 * at least currently on llvm 12.
+	 */
+	if (__builtin_constant_p(for_write)) {
+		if (for_write)
+			__builtin_prefetch(address, true);
+		else
+			__builtin_prefetch(address, false);
+	}
+}
+
+/**
+ * uds_prefetch_range() - Minimize cache-miss latency by attempting to move a range of addresses
+ *                        into a CPU cache before they are accessed.
+ *
+ * @start: the starting address to fetch (may be invalid)
+ * @size: the number of bytes in the address range
+ * @for_write: must be constant at compile time--false if for reading, true if for writing
+ */
+static inline void uds_prefetch_range(const void *start, unsigned int size,
+				      bool for_write)
+{
+	/*
+	 * Count the number of cache lines to fetch, allowing for the address range to span an
+	 * extra cache line boundary due to address alignment.
+	 */
+	const char *address = (const char *) start;
+	unsigned int offset = ((uintptr_t) address % L1_CACHE_BYTES);
+	unsigned int cache_lines = (1 + ((size + offset) / L1_CACHE_BYTES));
+
+	while (cache_lines-- > 0) {
+		uds_prefetch_address(address, for_write);
+		address += L1_CACHE_BYTES;
+	}
+}
+
+#endif /* UDS_CPU_H */