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/x86/entry/entry.S b/arch/x86/entry/entry.S
new file mode 100644
index 000000000..2bc217bb5
--- /dev/null
+++ b/arch/x86/entry/entry.S
@@ -0,0 +1,125 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Common place for both 32- and 64-bit entry routines.
+ */
+
+#include <linux/export.h>
+#include <linux/kvm_types.h>
+#include <linux/linkage.h>
+#include <linux/objtool.h>
+#include <asm/msr-index.h>
+#include <asm/unwind_hints.h>
+#include <asm/segment.h>
+#include <asm/cache.h>
+#include <asm/cpufeatures.h>
+#include <asm/nospec-branch.h>
+
+#include "calling.h"
+
+.pushsection .noinstr.text, "ax"
+
+/* Clobbers AX, CX, DX */
+SYM_FUNC_START(write_ibpb)
+	ANNOTATE_NOENDBR
+	movl	$MSR_IA32_PRED_CMD, %ecx
+	movl	_ASM_RIP(x86_pred_cmd), %eax
+	xorl	%edx, %edx
+	wrmsr
+
+	/* Make sure IBPB clears return stack preductions too. */
+	FILL_RETURN_BUFFER %rax, RSB_CLEAR_LOOPS, X86_BUG_IBPB_NO_RET
+	RET
+SYM_FUNC_END(write_ibpb)
+EXPORT_SYMBOL_FOR_KVM(write_ibpb);
+
+SYM_FUNC_START(__WARN_trap)
+	ANNOTATE_NOENDBR
+	ANNOTATE_REACHABLE
+	ud1 (%edx), %_ASM_ARG1
+	RET
+SYM_FUNC_END(__WARN_trap)
+EXPORT_SYMBOL(__WARN_trap)
+
+.popsection
+
+/*
+ * Define the VERW operand that is disguised as entry code so that
+ * it can be referenced with KPTI enabled. This ensures VERW can be
+ * used late in exit-to-user path after page tables are switched.
+ */
+.pushsection .entry.text, "ax"
+
+.align L1_CACHE_BYTES, 0xcc
+SYM_CODE_START_NOALIGN(x86_verw_sel)
+	UNWIND_HINT_UNDEFINED
+	ANNOTATE_NOENDBR
+	.word __KERNEL_DS
+.align L1_CACHE_BYTES, 0xcc
+SYM_CODE_END(x86_verw_sel);
+EXPORT_SYMBOL_FOR_KVM(x86_verw_sel);
+
+.popsection
+
+THUNK warn_thunk_thunk, __warn_thunk
+
+/*
+ * Clang's implementation of TLS stack cookies requires the variable in
+ * question to be a TLS variable. If the variable happens to be defined as an
+ * ordinary variable with external linkage in the same compilation unit (which
+ * amounts to the whole of vmlinux with LTO enabled), Clang will drop the
+ * segment register prefix from the references, resulting in broken code. Work
+ * around this by avoiding the symbol used in -mstack-protector-guard-symbol=
+ * entirely in the C code, and use an alias emitted by the linker script
+ * instead.
+ */
+#if defined(CONFIG_STACKPROTECTOR) && defined(CONFIG_SMP)
+EXPORT_SYMBOL(__ref_stack_chk_guard);
+#endif
+
+#if IS_ENABLED(CONFIG_KVM_INTEL)
+.macro IDT_DO_EVENT_IRQOFF call_insn call_target
+	/*
+	 * Unconditionally create a stack frame, getting the correct RSP on the
+	 * stack (for x86-64) would take two instructions anyways, and RBP can
+	 * be used to restore RSP to make objtool happy (see below).
+	 */
+	push %_ASM_BP
+	mov %_ASM_SP, %_ASM_BP
+
+#ifdef CONFIG_X86_64
+	/*
+	 * Align RSP to a 16-byte boundary (to emulate CPU behavior) before
+	 * creating the synthetic interrupt stack frame for the IRQ/NMI.
+	 */
+	and  $-16, %rsp
+	push $__KERNEL_DS
+	push %rbp
+#endif
+	pushf
+	push $__KERNEL_CS
+	\call_insn \call_target
+
+	/*
+	 * "Restore" RSP from RBP, even though IRET has already unwound RSP to
+	 * the correct value.  objtool doesn't know the callee will IRET and,
+	 * without the explicit restore, thinks the stack is getting walloped.
+	 * Using an unwind hint is problematic due to x86-64's dynamic alignment.
+	 */
+	leave
+	RET
+.endm
+
+#ifndef CONFIG_X86_64
+.pushsection .text, "ax"
+SYM_FUNC_START(idt_do_interrupt_irqoff)
+	IDT_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
+SYM_FUNC_END(idt_do_interrupt_irqoff)
+.popsection
+#endif
+
+.pushsection .noinstr.text, "ax"
+SYM_FUNC_START(idt_do_nmi_irqoff)
+	IDT_DO_EVENT_IRQOFF call asm_exc_nmi_kvm_vmx
+SYM_FUNC_END(idt_do_nmi_irqoff)
+.popsection
+#endif