[PATCH 31/35] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC_CTRL

[Peter Zijlstra]

From: Ashok Raj <ashok.raj@xxxxxxxxx>

Add some helper macros to save/restore MSR_IA32_SPEC_CTRL.

  stop_indirect_branch_speculation_and_save() - saves the current
	state and enables IBRS.

  restore_indirect_branch_speculation() - restores the previously
	saved IBRS state.

[peterz: renaming and folding of logic from the kvm patches]

Cc: Asit Mallick <asit.k.mallick@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Ashok Raj <ashok.raj@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/include/asm/nospec-branch.h |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -232,6 +232,24 @@ static inline void restart_indirect_bran
 		native_wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_DISABLE_IBRS);
 }
 
+static inline u64 stop_indirect_branch_speculation_and_save(void)
+{
+	u64 val = 0;
+
+	if (static_cpu_has(X86_FEATURE_IBRS)) {
+		val = native_rdmsrl(MSR_IA32_SPEC_CTRL);
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_ENABLE_IBRS);
+	}
+
+	return val;
+}
+
+static inline void restore_indirect_branch_speculation(u64 val)
+{
+	if (static_cpu_has(X86_FEATURE_IBRS))
+		native_wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
 void specctrl_init_ibpb(void);
 
 static inline void indirect_branch_prediction_barrier(void)