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, 50 insertions, 0 deletions

diff --git a/rust/ffi.rs b/rust/ffi.rs
new file mode 100644
index 000000000..f961e9728
--- /dev/null
+++ b/rust/ffi.rs
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Foreign function interface (FFI) types.
+//!
+//! This crate provides mapping from C primitive types to Rust ones.
+//!
+//! The Rust [`core`] crate provides [`core::ffi`], which maps integer types to the platform default
+//! C ABI. The kernel does not use [`core::ffi`], so it can customise the mapping that deviates from
+//! the platform default.
+
+#![no_std]
+
+macro_rules! alias {
+    ($($name:ident = $ty:ty;)*) => {$(
+        #[allow(non_camel_case_types, missing_docs)]
+        pub type $name = $ty;
+
+        // Check size compatibility with `core`.
+        const _: () = assert!(
+            ::core::mem::size_of::<$name>() == ::core::mem::size_of::<::core::ffi::$name>()
+        );
+    )*}
+}
+
+alias! {
+    // `core::ffi::c_char` is either `i8` or `u8` depending on architecture. In the kernel, we use
+    // `-funsigned-char` so it's always mapped to `u8`.
+    c_char = u8;
+
+    c_schar = i8;
+    c_uchar = u8;
+
+    c_short = i16;
+    c_ushort = u16;
+
+    c_int = i32;
+    c_uint = u32;
+
+    // In the kernel, `intptr_t` is defined to be `long` in all platforms, so we can map the type to
+    // `isize`.
+    c_long = isize;
+    c_ulong = usize;
+
+    c_longlong = i64;
+    c_ulonglong = u64;
+}
+
+pub use core::ffi::c_void;
+
+pub use core::ffi::CStr;