[v3 03/12] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions

[Chang S. Bae]

From: Andi Kleen <ak@xxxxxxxxxxxxxxx>

Add C intrinsics and assembler macros for the new FSBASE and GSBASE
instructions.

Very straight forward. Used in followon patches.

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

v2: Use __always_inline

[ chang: Revise the changelog. Place them in <asm/fsgsbase.h>. Replace
  the macros with GAS-compatible ones. ]

If GCC supports it, we can add -mfsgsbase to CFLAGS and use the builtins
here for extra performance.

Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/fsgsbase.h | 72 +++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
index eb377b6e9eed..b4d4509b786c 100644
--- a/arch/x86/include/asm/fsgsbase.h
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -19,6 +19,44 @@ extern unsigned long x86_gsbase_read_task(struct task_struct *task);
 extern int x86_fsbase_write_task(struct task_struct *task, unsigned long fsbase);
 extern int 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(".byte 0xf3, 0x48, 0x0f, 0xae, 0xc0 # rdfsbaseq %%rax"
+			: "=a" (fsbase)
+			:: "memory");
+
+	return fsbase;
+}
+
+static __always_inline unsigned long rdgsbase(void)
+{
+	unsigned long gsbase;
+
+	asm volatile(".byte 0xf3, 0x48, 0x0f, 0xae, 0xc8 # rdgsbaseq %%rax;"
+			: "=a" (gsbase)
+			:: "memory");
+
+	return gsbase;
+}
+
+static __always_inline void wrfsbase(unsigned long fsbase)
+{
+	asm volatile(".byte 0xf3, 0x48, 0x0f, 0xae, 0xd0 # wrfsbaseq %%rax"
+			:: "a" (fsbase)
+			: "memory");
+}
+
+static __always_inline void wrgsbase(unsigned long gsbase)
+{
+	asm volatile(".byte 0xf3, 0x48, 0x0f, 0xae, 0xd8 # wrgsbaseq %%rax;"
+			:: "a" (gsbase)
+			: "memory");
+}
+
 /* Helper functions for reading/writing FS/GS base */
 
 static inline unsigned long x86_fsbase_read_cpu(void)
@@ -44,6 +82,40 @@ extern void x86_gsbase_write_cpu_inactive(unsigned long gsbase);
 
 #endif /* CONFIG_X86_64 */
 
+#else /* __ASSEMBLY__ */
+
+#ifdef CONFIG_X86_64
+
+#include <asm/inst.h>
+
+.macro RDGSBASE opd
+	REG_TYPE rdgsbase_opd_type \opd
+	.if rdgsbase_opd_type == REG_TYPE_R64
+	R64_NUM rdgsbase_opd \opd
+	.byte 0xf3
+	PFX_REX rdgsbase_opd 0 W = 1
+	.else
+	.error "RDGSBASE: only for 64-bit value"
+	.endif
+	.byte 0xf, 0xae
+	MODRM 0xc0 rdgsbase_opd 1
+.endm
+
+.macro WRGSBASE opd
+	REG_TYPE wrgsbase_opd_type \opd
+	.if wrgsbase_opd_type == REG_TYPE_R64
+	R64_NUM wrgsbase_opd \opd
+	.byte 0xf3
+	PFX_REX wrgsbase_opd 0 W = 1
+	.else
+	.error "WRGSBASE: only for 64-bit value"
+	.endif
+	.byte 0xf, 0xae
+	MODRM 0xd0 wrgsbase_opd 1
+.endm
+
+#endif /* CONFIG_X86_64 */
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_FSGSBASE_H */
-- 
2.19.1