KVM: x86 emulator: disable writeback when decode dest operand

This patch change to disable writeback when decode dest
operand if the dest type is ImplicitOps or not specified.

Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 6 insertions, 17 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6c1e4d6c12cd..e0216eb8b574 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2627,9 +2627,6 @@ done_prefixes:
 
         /* Decode and fetch the destination operand: register or memory. */
         switch (c->d & DstMask) {
-        case ImplicitOps:
-                /* Special instructions do their own operand decoding. */
-                return 0;
         case DstReg:
                 decode_register_operand(&c->dst, c,
                          c->twobyte && (c->b == 0xb6 || c->b == 0xb7));
@@ -2664,6 +2661,11 @@ done_prefixes:
                                          c->regs[VCPU_REGS_RDI]);
                 c->dst.val = 0;
                 break;
+        case ImplicitOps:
+                /* Special instructions do their own operand decoding. */
+        default:
+                c->dst.type = OP_NONE; /* Disable writeback. */
+                return 0;
         }
 
 done:
@@ -3115,7 +3117,6 @@ special_insn:
         case 0xf5:      /* cmc */
                 /* complement carry flag from eflags reg */
                 ctxt->eflags ^= EFLG_CF;
-                c->dst.type = OP_NONE;  /* Disable writeback. */
                 break;
         case 0xf6 ... 0xf7:     /* Grp3 */
                 if (!emulate_grp3(ctxt, ops))
@@ -3123,16 +3124,13 @@ special_insn:
                 break;
         case 0xf8: /* clc */
                 ctxt->eflags &= ~EFLG_CF;
-                c->dst.type = OP_NONE;  /* Disable writeback. */
                 break;
         case 0xfa: /* cli */
                 if (emulator_bad_iopl(ctxt, ops)) {
                         emulate_gp(ctxt, 0);
                         goto done;
-                } else {
+                } else
                         ctxt->eflags &= ~X86_EFLAGS_IF;
-                        c->dst.type = OP_NONE;  /* Disable writeback. */
-                }
                 break;
         case 0xfb: /* sti */
                 if (emulator_bad_iopl(ctxt, ops)) {
@@ -3141,16 +3139,13 @@ special_insn:
                 } else {
                         ctxt->interruptibility = KVM_X86_SHADOW_INT_STI;
                         ctxt->eflags |= X86_EFLAGS_IF;
-                        c->dst.type = OP_NONE;  /* Disable writeback. */
                 }
                 break;
         case 0xfc: /* cld */
                 ctxt->eflags &= ~EFLG_DF;
-                c->dst.type = OP_NONE;  /* Disable writeback. */
                 break;
         case 0xfd: /* std */
                 ctxt->eflags |= EFLG_DF;
-                c->dst.type = OP_NONE;  /* Disable writeback. */
                 break;
         case 0xfe: /* Grp4 */
         grp45:
@@ -3287,16 +3282,13 @@ twobyte_insn:
                 break;
         case 0x06:
                 emulate_clts(ctxt->vcpu);
-                c->dst.type = OP_NONE;
                 break;
         case 0x09:              /* wbinvd */
                 kvm_emulate_wbinvd(ctxt->vcpu);
-                c->dst.type = OP_NONE;
                 break;
         case 0x08:              /* invd */
         case 0x0d:              /* GrpP (prefetch) */
         case 0x18:              /* Grp16 (prefetch/nop) */
-                c->dst.type = OP_NONE;
                 break;
         case 0x20: /* mov cr, reg */
                 switch (c->modrm_reg) {
@@ -3349,7 +3341,6 @@ twobyte_insn:
                         goto done;
                 }
                 rc = X86EMUL_CONTINUE;
-                c->dst.type = OP_NONE;
                 break;
         case 0x32:
                 /* rdmsr */
@@ -3361,7 +3352,6 @@ twobyte_insn:
                         c->regs[VCPU_REGS_RDX] = msr_data >> 32;
                 }
                 rc = X86EMUL_CONTINUE;
-                c->dst.type = OP_NONE;
                 break;
         case 0x34:              /* sysenter */
                 rc = emulate_sysenter(ctxt, ops);
@@ -3385,7 +3375,6 @@ twobyte_insn:
         case 0x80 ... 0x8f: /* jnz rel, etc*/
                 if (test_cc(c->b, ctxt->eflags))
                         jmp_rel(c, c->src.val);
-                c->dst.type = OP_NONE;
                 break;
         case 0xa0:        /* push fs */
                 emulate_push_sreg(ctxt, ops, VCPU_SREG_FS);