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-rw-r--r--arch/x86/kernel/process.h39
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);
+}