x86: adds paravirt hook for swapgs

This patch adds paravirt hook for swapgs operation, which is a privileged
operation in x86_64.

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/paravirt.c

@@ -390,6 +390,7 @@ struct pv_cpu_ops pv_cpu_ops = {
 
 	.irq_enable_syscall_ret = native_irq_enable_syscall_ret,
 	.iret = native_iret,
+	.swapgs = native_swapgs,
 
 	.set_iopl_mask = native_set_iopl_mask,
 	.io_delay = native_io_delay,

include/asm-x86/paravirt.h

@@ -127,6 +127,8 @@ struct pv_cpu_ops {
 	void (*irq_enable_syscall_ret)(void);
 	void (*iret)(void);
 
+	void (*swapgs)(void);
+
 	struct pv_lazy_ops lazy_mode;
 };
 
@@ -1228,6 +1230,13 @@ static inline unsigned long __raw_local_irq_save(void)
 	call *pv_cpu_ops+PV_CPU_read_cr0;	\
 	pop %edx; pop %ecx
 #else
+#define SWAPGS								\
+	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE,	\
+		  PV_SAVE_REGS;						\
+		  call *pv_cpu_ops+PV_CPU_swapgs;			\
+		  PV_RESTORE_REGS					\
+		 )
+
 #define GET_CR2_INTO_RCX			\
 	call *pv_mmu_ops+PV_MMU_read_cr2;	\
 	movq %rax, %rcx;			\

include/asm-x86/processor.h

@@ -435,6 +435,13 @@ static inline void native_load_sp0(struct tss_struct *tss,
 #endif
 }
 
+static inline void native_swapgs(void)
+{
+#ifdef CONFIG_X86_64
+	asm volatile("swapgs" ::: "memory");
+#endif
+}
+
 #ifdef CONFIG_PARAVIRT
 #include <asm/paravirt.h>
 #else
@@ -456,6 +463,7 @@ static inline void load_sp0(struct tss_struct *tss,
 }
 
 #define set_iopl_mask native_set_iopl_mask
+#define SWAPGS	swapgs
 #endif /* CONFIG_PARAVIRT */
 
 /*