linux-kernel - [PATCH v12 09/18] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions

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Date:   Mon, 11 May 2020 00:53:02 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, tglx@...utronix.de, bp@...en8.de,
        luto@...nel.org
Cc:     hpa@...or.com, dave.hansen@...el.com, tony.luck@...el.com,
        ak@...ux.intel.com, ravi.v.shankar@...el.com,
        chang.seok.bae@...el.com, Sasha Levin <sashal@...nel.org>
Subject: [PATCH v12 09/18] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions

From: Andi Kleen <ak@...ux.intel.com>

[ luto: Rename the variables from FS and GS to FSBASE and GSBASE and
  make <asm/fsgsbase.h> safe to include on 32-bit kernels. ]

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
Reviewed-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Reviewed-by: Tony Luck <tony.luck@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/include/asm/fsgsbase.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
index bca4c743de77c..fdd1177499b40 100644
--- a/arch/x86/include/asm/fsgsbase.h
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -19,6 +19,36 @@ extern unsigned long x86_gsbase_read_task(struct task_struct *task);
 extern void x86_fsbase_write_task(struct task_struct *task, unsigned long fsbase);
 extern void x86_gsbase_write_task(struct task_struct *task, unsigned long gsbase);
 
+/* Must be protected by X86_FEATURE_FSGSBASE check. */
+
+static __always_inline unsigned long rdfsbase(void)
+{
+	unsigned long fsbase;
+
+	asm volatile("rdfsbase %0" : "=r" (fsbase) :: "memory");
+
+	return fsbase;
+}
+
+static __always_inline unsigned long rdgsbase(void)
+{
+	unsigned long gsbase;
+
+	asm volatile("rdgsbase %0" : "=r" (gsbase) :: "memory");
+
+	return gsbase;
+}
+
+static __always_inline void wrfsbase(unsigned long fsbase)
+{
+	asm volatile("wrfsbase %0" :: "r" (fsbase) : "memory");
+}
+
+static __always_inline void wrgsbase(unsigned long gsbase)
+{
+	asm volatile("wrgsbase %0" :: "r" (gsbase) : "memory");
+}
+
 /* Helper functions for reading/writing FS/GS base */
 
 static inline unsigned long x86_fsbase_read_cpu(void)
-- 
2.20.1