KVM: emulate: clean up initializations in init_decode_cache

A lot of initializations are unnecessary as they get set to
appropriate values before actually being used. Optimize
placement of fields in x86_emulate_ctxt
Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_emulate.h

@@ -288,30 +288,32 @@ struct x86_emulate_ctxt {
 	u8 opcode_len;
 	u8 b;
 	u8 intercept;
-	u8 lock_prefix;
-	u8 rep_prefix;
 	u8 op_bytes;
 	u8 ad_bytes;
-	u8 rex_prefix;
 	struct operand src;
 	struct operand src2;
 	struct operand dst;
-	bool has_seg_override;
-	u8 seg_override;
-	u64 d;
 	int (*execute)(struct x86_emulate_ctxt *ctxt);
 	int (*check_perm)(struct x86_emulate_ctxt *ctxt);
+	bool has_seg_override;
+	bool rip_relative;
+	u8 rex_prefix;
+	u8 lock_prefix;
+	u8 rep_prefix;
+	u8 seg_override;
+	/* bitmaps of registers in _regs[] that can be read */
+	u32 regs_valid;
+	/* bitmaps of registers in _regs[] that have been written */
+	u32 regs_dirty;
 	/* modrm */
 	u8 modrm;
 	u8 modrm_mod;
 	u8 modrm_reg;
 	u8 modrm_rm;
 	u8 modrm_seg;
-	bool rip_relative;
+	u64 d;
 	unsigned long _eip;
 	struct operand memop;
-	u32 regs_valid;  /* bitmaps of registers in _regs[] that can be read */
-	u32 regs_dirty;  /* bitmaps of registers in _regs[] that have been written */
 	/* Fields above regs are cleared together. */
 	unsigned long _regs[NR_VCPU_REGS];
 	struct operand *memopp;

arch/x86/kvm/emulate.c

@@ -4534,14 +4534,11 @@ static int fastop(struct x86_emulate_ctxt *ctxt, void (*fop)(struct fastop *))
 
 void init_decode_cache(struct x86_emulate_ctxt *ctxt)
 {
-	memset(&ctxt->opcode_len, 0,
-	       (void *)&ctxt->_regs - (void *)&ctxt->opcode_len);
+	memset(&ctxt->has_seg_override, 0,
+	       (void *)&ctxt->modrm - (void *)&ctxt->has_seg_override);
 
-	ctxt->fetch.start = 0;
-	ctxt->fetch.end = 0;
 	ctxt->io_read.pos = 0;
 	ctxt->io_read.end = 0;
-	ctxt->mem_read.pos = 0;
 	ctxt->mem_read.end = 0;
 }