KVM: x86 emulator: centralize decoding of one-byte register access insns

Instructions like 'inc reg' that have the register operand encoded
in the opcode are currently specially decoded.  Extend
decode_register_operand() to handle that case, indicated by having
DstReg or SrcReg without ModRM.

Signed-off-by: Avi Kivity <avi@qumranet.com>

2 files changed, 47 insertions, 57 deletions

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 58ceb6616364..884e4a2e47e6 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -99,17 +99,13 @@ static u16 opcode_table[256] = {
         ByteOp | DstReg | SrcMem | ModRM, DstReg | SrcMem | ModRM,
         0, 0, 0, 0,
         /* 0x40 - 0x47 */
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
+        DstReg, DstReg, DstReg, DstReg, DstReg, DstReg, DstReg, DstReg,
         /* 0x48 - 0x4F */
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
+        DstReg, DstReg, DstReg, DstReg, DstReg, DstReg, DstReg, DstReg,
         /* 0x50 - 0x57 */
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
+        SrcReg, SrcReg, SrcReg, SrcReg, SrcReg, SrcReg, SrcReg, SrcReg,
         /* 0x58 - 0x5F */
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
-        ImplicitOps, ImplicitOps, ImplicitOps, ImplicitOps,
+        DstReg, DstReg, DstReg, DstReg, DstReg, DstReg, DstReg, DstReg,
         /* 0x60 - 0x67 */
         0, 0, 0, DstReg | SrcMem32 | ModRM | Mov /* movsxd (x86/64) */ ,
         0, 0, 0, 0,
@@ -525,13 +521,17 @@ static void decode_register_operand(struct operand *op,
                                     int highbyte_regs,
                                     int inhibit_bytereg)
 {
+        unsigned reg = c->modrm_reg;
+
+        if (!(c->d & ModRM))
+                reg = (c->b & 7) | ((c->rex_prefix & 1) << 3);
         op->type = OP_REG;
         if ((c->d & ByteOp) && !inhibit_bytereg) {
-                op->ptr = decode_register(c->modrm_reg, c->regs, highbyte_regs);
+                op->ptr = decode_register(reg, c->regs, highbyte_regs);
                 op->val = *(u8 *)op->ptr;
                 op->bytes = 1;
         } else {
-                op->ptr = decode_register(c->modrm_reg, c->regs, 0);
+                op->ptr = decode_register(reg, c->regs, 0);
                 op->bytes = c->op_bytes;
                 switch (op->bytes) {
                 case 2:
@@ -552,7 +552,7 @@ int
 x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 {
         struct decode_cache *c = &ctxt->decode;
-        u8 sib, rex_prefix = 0;
+        u8 sib;
         int rc = 0;
         int mode = ctxt->mode;
         int index_reg = 0, base_reg = 0, scale, rip_relative = 0;
@@ -616,7 +616,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
                 case 0x40 ... 0x4f: /* REX */
                         if (mode != X86EMUL_MODE_PROT64)
                                 goto done_prefixes;
-                        rex_prefix = c->b;
+                        c->rex_prefix = c->b;
                         continue;
                 case 0xf0:      /* LOCK */
                         c->lock_prefix = 1;
@@ -631,18 +631,18 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 
                 /* Any legacy prefix after a REX prefix nullifies its effect. */
 
-                rex_prefix = 0;
+                c->rex_prefix = 0;
         }
 
 done_prefixes:
 
         /* REX prefix. */
-        if (rex_prefix) {
-                if (rex_prefix & 8)
+        if (c->rex_prefix) {
+                if (c->rex_prefix & 8)
                         c->op_bytes = 8;        /* REX.W */
-                c->modrm_reg = (rex_prefix & 4) << 1;   /* REX.R */
-                index_reg = (rex_prefix & 2) << 2; /* REX.X */
-                c->modrm_rm = base_reg = (rex_prefix & 1) << 3; /* REG.B */
+                c->modrm_reg = (c->rex_prefix & 4) << 1;        /* REX.R */
+                index_reg = (c->rex_prefix & 2) << 2; /* REX.X */
+                c->modrm_rm = base_reg = (c->rex_prefix & 1) << 3; /* REG.B */
         }
 
         /* Opcode byte(s). */
@@ -837,7 +837,7 @@ modrm_done:
         case SrcNone:
                 break;
         case SrcReg:
-                decode_register_operand(&c->src, c, rex_prefix == 0, 0);
+                decode_register_operand(&c->src, c, c->rex_prefix == 0, 0);
                 break;
         case SrcMem16:
                 c->src.bytes = 2;
@@ -895,7 +895,7 @@ modrm_done:
                 /* Special instructions do their own operand decoding. */
                 return 0;
         case DstReg:
-                decode_register_operand(&c->dst, c, rex_prefix == 0,
+                decode_register_operand(&c->dst, c, c->rex_prefix == 0,
                          c->twobyte && (c->b == 0xb6 || c->b == 0xb7));
                 break;
         case DstMem:
@@ -1258,6 +1258,32 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
               cmp:              /* cmp */
                 emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags);
                 break;
+        case 0x40 ... 0x47: /* inc r16/r32 */
+                emulate_1op("inc", c->dst, ctxt->eflags);
+                break;
+        case 0x48 ... 0x4f: /* dec r16/r32 */
+                emulate_1op("dec", c->dst, ctxt->eflags);
+                break;
+        case 0x50 ... 0x57:  /* push reg */
+                c->dst.type  = OP_MEM;
+                c->dst.bytes = c->op_bytes;
+                c->dst.val = c->src.val;
+                register_address_increment(c->regs[VCPU_REGS_RSP],
+                                           -c->op_bytes);
+                c->dst.ptr = (void *) register_address(
+                        ctxt->ss_base, c->regs[VCPU_REGS_RSP]);
+                break;
+        case 0x58 ... 0x5f: /* pop reg */
+        pop_instruction:
+                if ((rc = ops->read_std(register_address(ctxt->ss_base,
+                        c->regs[VCPU_REGS_RSP]), c->dst.ptr,
+                        c->op_bytes, ctxt->vcpu)) != 0)
+                        goto done;
+
+                register_address_increment(c->regs[VCPU_REGS_RSP],
+                                           c->op_bytes);
+                c->dst.type = OP_NONE;  /* Disable writeback. */
+                break;
         case 0x63:              /* movsxd */
                 if (ctxt->mode != X86EMUL_MODE_PROT64)
                         goto cannot_emulate;
@@ -1373,43 +1399,6 @@ special_insn:
         if (c->twobyte)
                 goto twobyte_special_insn;
         switch (c->b) {
-        case 0x40 ... 0x47: /* inc r16/r32 */
-                c->dst.bytes = c->op_bytes;
-                c->dst.ptr = (unsigned long *)&c->regs[c->b & 0x7];
-                c->dst.val = *c->dst.ptr;
-                emulate_1op("inc", c->dst, ctxt->eflags);
-                break;
-        case 0x48 ... 0x4f: /* dec r16/r32 */
-                c->dst.bytes = c->op_bytes;
-                c->dst.ptr = (unsigned long *)&c->regs[c->b & 0x7];
-                c->dst.val = *c->dst.ptr;
-                emulate_1op("dec", c->dst, ctxt->eflags);
-                break;
-        case 0x50 ... 0x57:  /* push reg */
-                if (c->op_bytes == 2)
-                        c->src.val = (u16) c->regs[c->b & 0x7];
-                else
-                        c->src.val = (u32) c->regs[c->b & 0x7];
-                c->dst.type  = OP_MEM;
-                c->dst.bytes = c->op_bytes;
-                c->dst.val = c->src.val;
-                register_address_increment(c->regs[VCPU_REGS_RSP],
-                                           -c->op_bytes);
-                c->dst.ptr = (void *) register_address(
-                        ctxt->ss_base, c->regs[VCPU_REGS_RSP]);
-                break;
-        case 0x58 ... 0x5f: /* pop reg */
-                c->dst.ptr = (unsigned long *)&c->regs[c->b & 0x7];
-        pop_instruction:
-                if ((rc = ops->read_std(register_address(ctxt->ss_base,
-                        c->regs[VCPU_REGS_RSP]), c->dst.ptr,
-                        c->op_bytes, ctxt->vcpu)) != 0)
-                        goto done;
-
-                register_address_increment(c->regs[VCPU_REGS_RSP],
-                                           c->op_bytes);
-                c->dst.type = OP_NONE;  /* Disable writeback. */
-                break;
         case 0x6a: /* push imm8 */
                 c->src.val = 0L;
                 c->src.val = insn_fetch(s8, 1, c->eip);
diff --git a/drivers/kvm/x86_emulate.h b/drivers/kvm/x86_emulate.h
index f03b1287700a..e34868b42c33 100644
--- a/drivers/kvm/x86_emulate.h
+++ b/drivers/kvm/x86_emulate.h
@@ -126,6 +126,7 @@ struct decode_cache {
         u8 rep_prefix;
         u8 op_bytes;
         u8 ad_bytes;
+        u8 rex_prefix;
         struct operand src;
         struct operand dst;
         unsigned long *override_base;