1 files changed, 39 insertions, 0 deletions
diff --git a/arch/x86/kernel/process.h b/arch/x86/kernel/process.h
new file mode 100644
index 000000000..76b547b83
--- /dev/null
+++ b/arch/x86/kernel/process.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+//
+// Code shared between 32 and 64 bit
+
+#include <asm/spec-ctrl.h>
+
+void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p);
+
+/*
+ * This needs to be inline to optimize for the common case where no extra
+ * work needs to be done.
+ */
+static inline void switch_to_extra(struct task_struct *prev,
+				   struct task_struct *next)
+{
+	unsigned long next_tif = read_task_thread_flags(next);
+	unsigned long prev_tif = read_task_thread_flags(prev);
+
+	if (IS_ENABLED(CONFIG_SMP)) {
+		/*
+		 * Avoid __switch_to_xtra() invocation when conditional
+		 * STIBP is disabled and the only different bit is
+		 * TIF_SPEC_IB. For CONFIG_SMP=n TIF_SPEC_IB is not
+		 * in the TIF_WORK_CTXSW masks.
+		 */
+		if (!static_branch_likely(&switch_to_cond_stibp)) {
+			prev_tif &= ~_TIF_SPEC_IB;
+			next_tif &= ~_TIF_SPEC_IB;
+		}
+	}
+
+	/*
+	 * __switch_to_xtra() handles debug registers, i/o bitmaps,
+	 * speculation mitigations etc.
+	 */
+	if (unlikely(next_tif & _TIF_WORK_CTXSW_NEXT ||
+		     prev_tif & _TIF_WORK_CTXSW_PREV))
+		__switch_to_xtra(prev, next);
+}