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-rw-r--r--arch/x86/include/asm/thread_info.h13
-rw-r--r--arch/x86/kernel/process.h15
2 files changed, 26 insertions, 2 deletions
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index fa583ec99e3e..6d201699c651 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -147,9 +147,18 @@ struct thread_info {
_TIF_FSCHECK)
/* flags to check in __switch_to() */
-#define _TIF_WORK_CTXSW \
+#define _TIF_WORK_CTXSW_BASE \
(_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP| \
- _TIF_SSBD|_TIF_SPEC_IB)
+ _TIF_SSBD)
+
+/*
+ * Avoid calls to __switch_to_xtra() on UP as STIBP is not evaluated.
+ */
+#ifdef CONFIG_SMP
+# define _TIF_WORK_CTXSW (_TIF_WORK_CTXSW_BASE | _TIF_SPEC_IB)
+#else
+# define _TIF_WORK_CTXSW (_TIF_WORK_CTXSW_BASE)
+#endif
#define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)
#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)
diff --git a/arch/x86/kernel/process.h b/arch/x86/kernel/process.h
index 020fbfac3a27..898e97cf6629 100644
--- a/arch/x86/kernel/process.h
+++ b/arch/x86/kernel/process.h
@@ -2,6 +2,8 @@
//
// 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);
/*
@@ -14,6 +16,19 @@ static inline void switch_to_extra(struct task_struct *prev,
unsigned long next_tif = task_thread_info(next)->flags;
unsigned long prev_tif = task_thread_info(prev)->flags;
+ if (IS_ENABLED(CONFIG_SMP)) {
+ /*
+ * Avoid __switch_to_xtra() invocation when conditional
+ * STIPB 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.