[PATCH 2/4] KVM: x86 emulator: Make prefix decoding a separate function

[Takuya Yoshikawa <takuya.yoshikawa@xxxxxxxxx>]

From: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>

Instruction decoding can be split into separate parts, and this is the
first one which treats the instruction prefixes.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx>
Cc: Takuya Yoshikawa <takuya.yoshikawa@xxxxxxxxx>
---
 arch/x86/kvm/emulate.c |   58 +++++++++++++++++++++++++++++++----------------
 1 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 5a49290..b22238b 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3874,22 +3874,21 @@ done:
 	return rc;
 }
 
-int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
+/**
+ * decode_prefixes - decode instruction prefixes
+ * @ctxt: emulation context
+ *
+ * Fetches instruction prefixes and sets some ctxt fields based on them.
+ * The byte next to the last prefix is also fetched into ctxt->b.
+ *
+ * Returns X86EMUL_CONTINUE on success.
+ */
+static int decode_prefixes(struct x86_emulate_ctxt *ctxt)
 {
 	int rc = X86EMUL_CONTINUE;
-	int mode = ctxt->mode;
-	int def_op_bytes, def_ad_bytes, goffset, simd_prefix;
-	struct opcode opcode;
+	int def_op_bytes, def_ad_bytes;
 
-	ctxt->memop.type = OP_NONE;
-	ctxt->memopp = NULL;
-	ctxt->_eip = ctxt->eip;
-	ctxt->fetch.start = ctxt->_eip;
-	ctxt->fetch.end = ctxt->fetch.start + insn_len;
-	if (insn_len > 0)
-		memcpy(ctxt->fetch.data, insn, insn_len);
-
-	switch (mode) {
+	switch (ctxt->mode) {
 	case X86EMUL_MODE_REAL:
 	case X86EMUL_MODE_VM86:
 	case X86EMUL_MODE_PROT16:
@@ -3905,7 +3904,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 		break;
 #endif
 	default:
-		return EMULATION_FAILED;
+		return X86EMUL_UNHANDLEABLE;
 	}
 
 	ctxt->op_bytes = def_op_bytes;
@@ -3920,7 +3919,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 			ctxt->op_bytes = def_op_bytes ^ 6;
 			break;
 		case 0x67:	/* address-size override */
-			if (mode == X86EMUL_MODE_PROT64)
+			if (ctxt->mode == X86EMUL_MODE_PROT64)
 				/* switch between 4/8 bytes */
 				ctxt->ad_bytes = def_ad_bytes ^ 12;
 			else
@@ -3938,7 +3937,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 			set_seg_override(ctxt, ctxt->b & 7);
 			break;
 		case 0x40 ... 0x4f: /* REX */
-			if (mode != X86EMUL_MODE_PROT64)
+			if (ctxt->mode != X86EMUL_MODE_PROT64)
 				goto done_prefixes;
 			ctxt->rex_prefix = ctxt->b;
 			continue;
@@ -3954,15 +3953,34 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 		}
 
 		/* Any legacy prefix after a REX prefix nullifies its effect. */
-
 		ctxt->rex_prefix = 0;
 	}
 
 done_prefixes:
-
 	/* REX prefix. */
 	if (ctxt->rex_prefix & 8)
 		ctxt->op_bytes = 8;	/* REX.W */
+done:
+	return rc;
+}
+
+int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
+{
+	int rc = X86EMUL_CONTINUE;
+	int goffset, simd_prefix;
+	struct opcode opcode;
+
+	ctxt->memop.type = OP_NONE;
+	ctxt->memopp = NULL;
+	ctxt->_eip = ctxt->eip;
+	ctxt->fetch.start = ctxt->_eip;
+	ctxt->fetch.end = ctxt->fetch.start + insn_len;
+	if (insn_len > 0)
+		memcpy(ctxt->fetch.data, insn, insn_len);
+
+	rc = decode_prefixes(ctxt);
+	if (rc != X86EMUL_CONTINUE)
+		goto done;
 
 	/* Opcode byte(s). */
 	opcode = opcode_table[ctxt->b];
@@ -4025,11 +4043,11 @@ done_prefixes:
 	if (!(ctxt->d & VendorSpecific) && ctxt->only_vendor_specific_insn)
 		return EMULATION_FAILED;
 
-	if (mode == X86EMUL_MODE_PROT64 && (ctxt->d & Stack))
+	if (ctxt->mode == X86EMUL_MODE_PROT64 && (ctxt->d & Stack))
 		ctxt->op_bytes = 8;
 
 	if (ctxt->d & Op3264) {
-		if (mode == X86EMUL_MODE_PROT64)
+		if (ctxt->mode == X86EMUL_MODE_PROT64)
 			ctxt->op_bytes = 8;
 		else
 			ctxt->op_bytes = 4;
-- 
1.7.5.4

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html