[PATCH 2/5] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC_CTRL

[Ashok Raj]

Add some helper macros to save/restore MSR_IA32_SPEC_CTRL.

Although we could use the spec_ctrl_unprotected_begin/end macros they seem
be bit unreadable for some uses.

spec_ctrl_get - read MSR_IA32_SPEC_CTRL to save
spec_ctrl_set - write value restore MSR_IA32_SPEC_CTRL
spec_ctrl_restriction_off - same as spec_ctrl_unprotected_begin
spec_ctrl_restriction_on - same as spec_ctrl_unprotected_end

Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
---
 arch/x86/include/asm/spec_ctrl.h | 12 ++++++++++++
 arch/x86/kernel/cpu/spec_ctrl.c  | 11 +++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/x86/include/asm/spec_ctrl.h b/arch/x86/include/asm/spec_ctrl.h
index 2dfa31b..926feb2 100644
--- a/arch/x86/include/asm/spec_ctrl.h
+++ b/arch/x86/include/asm/spec_ctrl.h
@@ -9,6 +9,10 @@
 void spec_ctrl_scan_feature(struct cpuinfo_x86 *c);
 void spec_ctrl_unprotected_begin(void);
 void spec_ctrl_unprotected_end(void);
+void spec_ctrl_set(u64 val);
+
+#define spec_ctrl_restriction_on	spec_ctrl_unprotected_end
+#define spec_ctrl_restriction_off	spec_ctrl_unprotected_begin
 
 static inline u64 native_rdmsrl(unsigned int msr)
 {
@@ -34,4 +38,12 @@ static inline void __enable_indirect_speculation(void)
 	native_wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_DISABLE_IBRS);
 }
 
+static inline u64 spec_ctrl_get(void)
+{
+	u64 val;
+
+	val = native_rdmsrl(MSR_IA32_SPEC_CTRL);
+
+	return val;
+}
 #endif /* _ASM_X86_SPEC_CTRL_H */
diff --git a/arch/x86/kernel/cpu/spec_ctrl.c b/arch/x86/kernel/cpu/spec_ctrl.c
index 9e9d013..02fc630 100644
--- a/arch/x86/kernel/cpu/spec_ctrl.c
+++ b/arch/x86/kernel/cpu/spec_ctrl.c
@@ -47,3 +47,14 @@ void spec_ctrl_unprotected_end(void)
 		__disable_indirect_speculation();
 }
 EXPORT_SYMBOL_GPL(spec_ctrl_unprotected_end);
+
+void spec_ctrl_set(u64 val)
+{
+	if (boot_cpu_has(X86_FEATURE_SPEC_CTRL)) {
+		if (!val) {
+			spec_ctrl_restriction_off();
+		} else
+			spec_ctrl_restriction_on();
+	}
+}
+EXPORT_SYMBOL(spec_ctrl_set);
-- 
2.7.4