linux-kernel - [PATCH 2/5] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC

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Date:   Thu, 11 Jan 2018 17:32:16 -0800
From:   Ashok Raj <ashok.raj@...el.com>
To:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     Ashok Raj <ashok.raj@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>
Subject: [PATCH 2/5] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC_CTRL

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@...el.com>
---
 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