x86/paravirt: selectively save/restore regs around pvops calls

Impact: Optimization

Each asm paravirt-ops call says what registers are available for
clobbering.  This patch makes use of this to selectively save/restore
registers around each pvops call.  In many cases this significantly
shrinks code size.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/paravirt.h

@@ -12,19 +12,29 @@
 #define CLBR_EAX  (1 << 0)
 #define CLBR_ECX  (1 << 1)
 #define CLBR_EDX  (1 << 2)
+#define CLBR_EDI  (1 << 3)
 
-#ifdef CONFIG_X86_64
-#define CLBR_RSI  (1 << 3)
-#define CLBR_RDI  (1 << 4)
+#ifdef CONFIG_X86_32
+/* CLBR_ANY should match all regs platform has. For i386, that's just it */
+#define CLBR_ANY  ((1 << 4) - 1)
+#else
+#define CLBR_RAX  CLBR_EAX
+#define CLBR_RCX  CLBR_ECX
+#define CLBR_RDX  CLBR_EDX
+#define CLBR_RDI  CLBR_EDI
+#define CLBR_RSI  (1 << 4)
 #define CLBR_R8   (1 << 5)
 #define CLBR_R9   (1 << 6)
 #define CLBR_R10  (1 << 7)
 #define CLBR_R11  (1 << 8)
 #define CLBR_ANY  ((1 << 9) - 1)
+
+#define CLBR_ARG_REGS	(CLBR_RDI | CLBR_RSI | CLBR_RDX | \
+			 CLBR_RCX | CLBR_R8 | CLBR_R9)
+#define CLBR_RET_REG	(CLBR_RAX | CLBR_RDX)
+#define CLBR_SCRATCH	(CLBR_R10 | CLBR_R11)
+
 #include <asm/desc_defs.h>
-#else
-/* CLBR_ANY should match all regs platform has. For i386, that's just it */
-#define CLBR_ANY  ((1 << 3) - 1)
 #endif /* X86_64 */
 
 #ifndef __ASSEMBLY__
@@ -1530,33 +1540,49 @@ static inline unsigned long __raw_local_irq_save(void)
 	.popsection
 
 
+#define COND_PUSH(set, mask, reg)			\
+	.if ((~set) & mask); push %reg; .endif
+#define COND_POP(set, mask, reg)			\
+	.if ((~set) & mask); pop %reg; .endif
+
 #ifdef CONFIG_X86_64
-#define PV_SAVE_REGS				\
-	push %rax;				\
-	push %rcx;				\
-	push %rdx;				\
-	push %rsi;				\
-	push %rdi;				\
-	push %r8;				\
-	push %r9;				\
-	push %r10;				\
-	push %r11
-#define PV_RESTORE_REGS				\
-	pop %r11;				\
-	pop %r10;				\
-	pop %r9;				\
-	pop %r8;				\
-	pop %rdi;				\
-	pop %rsi;				\
-	pop %rdx;				\
-	pop %rcx;				\
-	pop %rax
+
+#define PV_SAVE_REGS(set)			\
+	COND_PUSH(set, CLBR_RAX, rax);		\
+	COND_PUSH(set, CLBR_RCX, rcx);		\
+	COND_PUSH(set, CLBR_RDX, rdx);		\
+	COND_PUSH(set, CLBR_RSI, rsi);		\
+	COND_PUSH(set, CLBR_RDI, rdi);		\
+	COND_PUSH(set, CLBR_R8, r8);		\
+	COND_PUSH(set, CLBR_R9, r9);		\
+	COND_PUSH(set, CLBR_R10, r10);		\
+	COND_PUSH(set, CLBR_R11, r11)
+#define PV_RESTORE_REGS(set)			\
+	COND_POP(set, CLBR_R11, r11);		\
+	COND_POP(set, CLBR_R10, r10);		\
+	COND_POP(set, CLBR_R9, r9);		\
+	COND_POP(set, CLBR_R8, r8);		\
+	COND_POP(set, CLBR_RDI, rdi);		\
+	COND_POP(set, CLBR_RSI, rsi);		\
+	COND_POP(set, CLBR_RDX, rdx);		\
+	COND_POP(set, CLBR_RCX, rcx);		\
+	COND_POP(set, CLBR_RAX, rax)
+
 #define PARA_PATCH(struct, off)        ((PARAVIRT_PATCH_##struct + (off)) / 8)
 #define PARA_SITE(ptype, clobbers, ops) _PVSITE(ptype, clobbers, ops, .quad, 8)
 #define PARA_INDIRECT(addr)	*addr(%rip)
 #else
-#define PV_SAVE_REGS   pushl %eax; pushl %edi; pushl %ecx; pushl %edx
-#define PV_RESTORE_REGS popl %edx; popl %ecx; popl %edi; popl %eax
+#define PV_SAVE_REGS(set)			\
+	COND_PUSH(set, CLBR_EAX, eax);		\
+	COND_PUSH(set, CLBR_EDI, edi);		\
+	COND_PUSH(set, CLBR_ECX, ecx);		\
+	COND_PUSH(set, CLBR_EDX, edx)
+#define PV_RESTORE_REGS(set)			\
+	COND_POP(set, CLBR_EDX, edx);		\
+	COND_POP(set, CLBR_ECX, ecx);		\
+	COND_POP(set, CLBR_EDI, edi);		\
+	COND_POP(set, CLBR_EAX, eax)
+
 #define PARA_PATCH(struct, off)        ((PARAVIRT_PATCH_##struct + (off)) / 4)
 #define PARA_SITE(ptype, clobbers, ops) _PVSITE(ptype, clobbers, ops, .long, 4)
 #define PARA_INDIRECT(addr)	*%cs:addr
@@ -1568,15 +1594,15 @@ static inline unsigned long __raw_local_irq_save(void)
 
 #define DISABLE_INTERRUPTS(clobbers)					\
 	PARA_SITE(PARA_PATCH(pv_irq_ops, PV_IRQ_irq_disable), clobbers, \
-		  PV_SAVE_REGS;						\
+		  PV_SAVE_REGS(clobbers);				\
 		  call PARA_INDIRECT(pv_irq_ops+PV_IRQ_irq_disable);	\
-		  PV_RESTORE_REGS;)			\
+		  PV_RESTORE_REGS(clobbers);)
 
 #define ENABLE_INTERRUPTS(clobbers)					\
 	PARA_SITE(PARA_PATCH(pv_irq_ops, PV_IRQ_irq_enable), clobbers,	\
-		  PV_SAVE_REGS;						\
+		  PV_SAVE_REGS(clobbers);				\
 		  call PARA_INDIRECT(pv_irq_ops+PV_IRQ_irq_enable);	\
-		  PV_RESTORE_REGS;)
+		  PV_RESTORE_REGS(clobbers);)
 
 #define USERGS_SYSRET32							\
 	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret32),	\
@@ -1606,11 +1632,15 @@ static inline unsigned long __raw_local_irq_save(void)
 	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE,	\
 		  swapgs)
 
+/*
+ * Note: swapgs is very special, and in practise is either going to be
+ * implemented with a single "swapgs" instruction or something very
+ * special.  Either way, we don't need to save any registers for
+ * it.
+ */
 #define SWAPGS								\
 	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_swapgs), CLBR_NONE,	\
-		  PV_SAVE_REGS;						\
-		  call PARA_INDIRECT(pv_cpu_ops+PV_CPU_swapgs);		\
-		  PV_RESTORE_REGS					\
+		  call PARA_INDIRECT(pv_cpu_ops+PV_CPU_swapgs)		\
 		 )
 
 #define GET_CR2_INTO_RCX				\