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Subject[PATCH V2 08/15] x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions
Date
From: Andi Kleen <ak@linux.intel.com>

Add C intrinsics and assembler macros for the new RD/WR FS/GS BASE
instructions.

Very straight forward. Used in followon patch.

[luto: rename the variables from fs and gs to fsbase and gsbase and
make fsgs.h safe to include on 32-bit kernels.]

v2: Use __always_inline

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
[chang: Replace new instruction macros with GAS-compatible and
renaming. Note: if GCC supports it, we can add -mfsgsbase to
CFLAGS and use the builtins here for extra performance.]
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/fsgsbase.h | 70 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 70 insertions(+)

diff --git a/arch/x86/include/asm/fsgsbase.h b/arch/x86/include/asm/fsgsbase.h
index 0d4fbef..ed42015 100644
--- a/arch/x86/include/asm/fsgsbase.h
+++ b/arch/x86/include/asm/fsgsbase.h
@@ -18,6 +18,42 @@ unsigned long read_task_gsbase(struct task_struct *task);
int write_task_fsbase(struct task_struct *task, unsigned long fsbase);
int write_task_gsbase(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 read_fsbase(void)
@@ -42,6 +78,40 @@ void write_inactive_gsbase(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 */
--
2.7.4
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