Index: lib/Target/ARM/Disassembler/ARMDisassembler.cpp
===================================================================
--- lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -3974,7 +3974,53 @@
 
 static DecodeStatus DecodeMSRMask(MCInst &Inst, unsigned Val,
                           uint64_t Address, const void *Decoder) {
-  if (!Val) return MCDisassembler::Fail;
+  uint64_t FeatureBits = ((const MCDisassembler*)Decoder)->getSubtargetInfo()
+                                                          .getFeatureBits();
+  if (FeatureBits & ARM::FeatureMClass) {
+    unsigned ValLow = Val & 0xff;
+
+    // Validate the SYSm value first.
+    switch (ValLow) {
+    case  0: // apsr
+    case  1: // iapsr
+    case  2: // eapsr
+    case  3: // xpsr
+    case  5: // ipsr
+    case  6: // epsr
+    case  7: // iepsr
+    case  8: // msp
+    case  9: // psp
+    case 16: // primask
+    case 20: // control
+      break;
+    case 17: // basepri
+    case 18: // basepri_max
+    case 19: // faultmask
+      if (!(FeatureBits & ARM::HasV7Ops))
+        // Values basepri, basepri_max and faultmask are only valid for v7m.
+        return MCDisassembler::Fail;
+      break;
+    default:
+      return MCDisassembler::Fail;
+    }
+
+    // The ARMv7-M architecture has an additional 2-bit mask value in the MSR
+    // instruction (bits {11,10}). The mask is used only with apsr, iapsr,
+    // eapsr and xpsr, it has to be 0b10 in other cases. Bit mask{1} indicates
+    // if the NZCVQ bits should be moved by the instruction. Bit mask{0}
+    // indicates the move for the GE{3:0} bits, the mask{0} bit can be set
+    // only if the processor includes the DSP extension.
+    if ((FeatureBits & ARM::HasV7Ops) && Inst.getOpcode() == ARM::t2MSR_M) {
+      unsigned Mask = (Val >> 10) & 3;
+      if (Mask == 0 || (Mask != 2 && ValLow > 3) ||
+          (!(FeatureBits & ARM::FeatureDSPThumb2) && Mask == 1))
+        return MCDisassembler::Fail;
+    }
+  } else {
+    // A/R class
+    if (Val == 0)
+      return MCDisassembler::Fail;
+  }
   Inst.addOperand(MCOperand::CreateImm(Val));
   return MCDisassembler::Success;
 }
Index: test/MC/Disassembler/ARM/invalid-thumb-MSR-MClass.txt
===================================================================
--- /dev/null
+++ test/MC/Disassembler/ARM/invalid-thumb-MSR-MClass.txt
@@ -0,0 +1,34 @@
+# RUN: not llvm-mc -disassemble %s -triple=thumbv7-apple-darwin9 -mcpu cortex-m3 2>&1 | FileCheck %s
+
+#------------------------------------------------------------------------------
+# Undefined encodings for mrs
+#------------------------------------------------------------------------------
+
+# invalid SYSm
+# CHECK: warning: invalid instruction encoding
+# CHECK-NEXT: [0xef 0xf3 0x80 0x80]
+[0xef 0xf3 0x80 0x80]
+
+#------------------------------------------------------------------------------
+# Undefined encodings for msr
+#------------------------------------------------------------------------------
+
+# invalid mask = '00'
+# CHECK: warning: invalid instruction encoding
+# CHECK-NEXT: [0x80 0xf3 0x00 0x80]
+[0x80 0xf3 0x00 0x80]
+
+# invalid mask = '11' with SYSm not in {0..3}
+# CHECK: warning: invalid instruction encoding
+# CHECK-NEXT: [0x80 0xf3 0x04 0x8c]
+[0x80 0xf3 0x04 0x8c]
+
+# invalid mask = '01' (Cortex-M3 does not have the DSP extension)
+# CHECK: warning: invalid instruction encoding
+# CHECK-NEXT: [0x80 0xf3 0x00 0x84]
+[0x80 0xf3 0x00 0x84]
+
+# invalid SYSm
+# CHECK: warning: invalid instruction encoding
+# CHECK-NEXT: [0x80 0xf3 0x80 0x88]
+[0x80 0xf3 0x80 0x88]
Index: test/MC/Disassembler/ARM/thumb-MSR-MClass.txt
===================================================================
--- test/MC/Disassembler/ARM/thumb-MSR-MClass.txt
+++ test/MC/Disassembler/ARM/thumb-MSR-MClass.txt
@@ -1,7 +1,94 @@
-# RUN: llvm-mc --disassemble %s -triple=thumbv7-apple-darwin9 -mcpu cortex-m3 | FileCheck %s
+# RUN: llvm-mc --disassemble %s -triple=thumbv7-apple-darwin9 -mcpu cortex-m4 | FileCheck %s
 
-# CHECK: msr    primask, r0
-0x80 0xf3 0x10 0x80
+#------------------------------------------------------------------------------
+# MRS
+#------------------------------------------------------------------------------
 
-# CHECK: mrs    r0, primask
+# CHECK: mrs r0, apsr
+# CHECK: mrs r0, iapsr
+# CHECK: mrs r0, eapsr
+# CHECK: mrs r0, xpsr
+# CHECK: mrs r0, ipsr
+# CHECK: mrs r0, epsr
+# CHECK: mrs r0, iepsr
+# CHECK: mrs r0, msp
+# CHECK: mrs r0, psp
+# CHECK: mrs r0, primask
+# CHECK: mrs r0, basepri
+# CHECK: mrs r0, basepri_max
+# CHECK: mrs r0, faultmask
+# CHECK: mrs r0, control
+
+0xef 0xf3 0x00 0x80
+0xef 0xf3 0x01 0x80
+0xef 0xf3 0x02 0x80
+0xef 0xf3 0x03 0x80
+0xef 0xf3 0x05 0x80
+0xef 0xf3 0x06 0x80
+0xef 0xf3 0x07 0x80
+0xef 0xf3 0x08 0x80
+0xef 0xf3 0x09 0x80
 0xef 0xf3 0x10 0x80
+0xef 0xf3 0x11 0x80
+0xef 0xf3 0x12 0x80
+0xef 0xf3 0x13 0x80
+0xef 0xf3 0x14 0x80
+
+
+#------------------------------------------------------------------------------
+# MSR
+#------------------------------------------------------------------------------
+
+# CHECK: msr apsr, r0
+# CHECK: msr apsr_g, r0
+# CHECK: msr apsr_nzcvqg, r0
+
+0x80 0xf3 0x00 0x88
+0x80 0xf3 0x00 0x84
+0x80 0xf3 0x00 0x8c
+
+# CHECK: msr iapsr, r0
+# CHECK: msr iapsr_g, r0
+# CHECK: msr iapsr_nzcvqg, r0
+
+0x80 0xf3 0x01 0x88
+0x80 0xf3 0x01 0x84
+0x80 0xf3 0x01 0x8c
+
+# CHECK: msr eapsr, r0
+# CHECK: msr eapsr_g, r0
+# CHECK: msr eapsr_nzcvqg, r0
+
+0x80 0xf3 0x02 0x88
+0x80 0xf3 0x02 0x84
+0x80 0xf3 0x02 0x8c
+
+# CHECK: msr xpsr, r0
+# CHECK: msr xpsr_g, r0
+# CHECK: msr xpsr_nzcvqg, r0
+
+0x80 0xf3 0x03 0x88
+0x80 0xf3 0x03 0x84
+0x80 0xf3 0x03 0x8c
+
+# CHECK: msr ipsr, r0
+# CHECK: msr epsr, r0
+# CHECK: msr iepsr, r0
+# CHECK: msr msp, r0
+# CHECK: msr psp, r0
+# CHECK: msr primask, r0
+# CHECK: msr basepri, r0
+# CHECK: msr basepri_max, r0
+# CHECK: msr faultmask, r0
+# CHECK: msr control, r0
+
+0x80 0xf3 0x05 0x88
+0x80 0xf3 0x06 0x88
+0x80 0xf3 0x07 0x88
+0x80 0xf3 0x08 0x88
+0x80 0xf3 0x09 0x88
+0x80 0xf3 0x10 0x88
+0x80 0xf3 0x11 0x88
+0x80 0xf3 0x12 0x88
+0x80 0xf3 0x13 0x88
+0x80 0xf3 0x14 0x88