KVM: x86: MOVNTI emulation min opsize is not respected

Commit 3b32004 ("KVM: x86: movnti minimum op size of 32-bit is not kept")
did not fully fix the minimum operand size of MONTI emulation. Still, MOVNTI
may be mistakenly performed using 16-bit opsize.

This patch add No16 flag to mark an instruction does not support 16-bits
operand size.

Signed-off-by: Nadav Amit <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: anadav

arch/x86/kvm/emulate.c

@@ -167,6 +167,7 @@
 #define NoBigReal   ((u64)1 << 50)  /* No big real mode */
 #define PrivUD      ((u64)1 << 51)  /* #UD instead of #GP on CPL > 0 */
 #define NearBranch  ((u64)1 << 52)  /* Near branches */
+#define No16	    ((u64)1 << 53)  /* No 16 bit operand */
 
 #define DstXacc     (DstAccLo | SrcAccHi | SrcWrite)
 
@@ -4134,7 +4135,7 @@ static const struct opcode twobyte_table[256] = {
 	D(DstReg | SrcMem8 | ModRM | Mov), D(DstReg | SrcMem16 | ModRM | Mov),
 	/* 0xC0 - 0xC7 */
 	F2bv(DstMem | SrcReg | ModRM | SrcWrite | Lock, em_xadd),
-	N, D(DstMem | SrcReg | ModRM | Mov),
+	N, I(DstMem | SrcReg | ModRM | No16 | Mov, em_mov),
 	N, N, N, GD(0, &group9),
 	/* 0xC8 - 0xCF */
 	X8(I(DstReg, em_bswap)),
@@ -4571,7 +4572,8 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 		return EMULATION_FAILED;
 
 	if (unlikely(ctxt->d &
-	    (NotImpl|Stack|Op3264|Sse|Mmx|Intercept|CheckPerm|NearBranch))) {
+	    (NotImpl|Stack|Op3264|Sse|Mmx|Intercept|CheckPerm|NearBranch|
+	     No16))) {
 		/*
 		 * These are copied unconditionally here, and checked unconditionally
 		 * in x86_emulate_insn.
@@ -4596,6 +4598,9 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 				ctxt->op_bytes = 4;
 		}
 
+		if ((ctxt->d & No16) && ctxt->op_bytes == 2)
+			ctxt->op_bytes = 4;
+
 		if (ctxt->d & Sse)
 			ctxt->op_bytes = 16;
 		else if (ctxt->d & Mmx)
@@ -5061,11 +5066,6 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
 		ctxt->dst.val = (ctxt->src.bytes == 1) ? (s8) ctxt->src.val :
 							(s16) ctxt->src.val;
 		break;
-	case 0xc3:		/* movnti */
-		ctxt->dst.bytes = ctxt->op_bytes;
-		ctxt->dst.val = (ctxt->op_bytes == 8) ? (u64) ctxt->src.val :
-							(u32) ctxt->src.val;
-		break;
 	default:
 		goto cannot_emulate;
 	}