[PATCH v6 1/4] x86/speculation: Add __update_spec_ctrl() helper

[Waiman Long]

Add a new __update_spec_ctrl() helper which is a variant of
update_spec_ctrl() that can be used in a noinstr function.

Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---
 arch/x86/include/asm/spec-ctrl.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/spec-ctrl.h b/arch/x86/include/asm/spec-ctrl.h
index cb0386fc4dc3..d03408e0468a 100644
--- a/arch/x86/include/asm/spec-ctrl.h
+++ b/arch/x86/include/asm/spec-ctrl.h
@@ -4,6 +4,7 @@
 
 #include <linux/thread_info.h>
 #include <asm/nospec-branch.h>
+#include <asm/msr.h>
 
 /*
  * On VMENTER we must preserve whatever view of the SPEC_CTRL MSR
@@ -76,6 +77,16 @@ static inline u64 ssbd_tif_to_amd_ls_cfg(u64 tifn)
 	return (tifn & _TIF_SSBD) ? x86_amd_ls_cfg_ssbd_mask : 0ULL;
 }
 
+/*
+ * This can be used in noinstr function & should only be called in bare
+ * metal context.
+ */
+static __always_inline void __update_spec_ctrl(u64 val)
+{
+	__this_cpu_write(x86_spec_ctrl_current, val);
+	native_wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
 #ifdef CONFIG_SMP
 extern void speculative_store_bypass_ht_init(void);
 #else
-- 
2.31.1