Index: lib/Target/AArch64/AArch64SystemOperands.td
===================================================================
--- lib/Target/AArch64/AArch64SystemOperands.td
+++ lib/Target/AArch64/AArch64SystemOperands.td
@@ -1457,6 +1457,7 @@
 def : RWSysReg<"TFSR_EL3",         0b11, 0b110, 0b0110, 0b0110, 0b000>;
 def : RWSysReg<"TFSR_EL12",        0b11, 0b101, 0b0110, 0b0110, 0b000>;
 def : RWSysReg<"TFSRE0_EL1",       0b11, 0b000, 0b0110, 0b0110, 0b001>;
+def : ROSysReg<"GMID_EL1",         0b11, 0b001, 0b0000, 0b0000, 0b100>;
 } // HasMTE
 
 // Cyclone specific system registers
Index: test/MC/AArch64/armv8.5a-mte-error.s
===================================================================
--- test/MC/AArch64/armv8.5a-mte-error.s
+++ test/MC/AArch64/armv8.5a-mte-error.s
@@ -553,6 +553,7 @@
 mrs tfsr_el3
 mrs tfsr_el12
 mrs tfsre0_el1
+mrs gmid_el1
 
 // CHECK:      invalid operand for instruction
 // CHECK-NEXT: tco
@@ -570,6 +571,8 @@
 // CHECK-NEXT: tfsr_el12
 // CHECK:      invalid operand for instruction
 // CHECK-NEXT: tfsre0_el1
+// CHECK:      invalid operand for instruction
+// CHECK-NEXT: gmid_el1
 
 mrs tco, #0
 mrs tco, x0
@@ -580,6 +583,7 @@
 mrs tfsr_el3, x5
 mrs tfsr_el12, x6
 mrs tfsre0_el1, x7
+mrs gmid_el1, x7
 
 // CHECK:      invalid operand for instruction
 // CHECK-NEXT: tco, #0
@@ -599,6 +603,8 @@
 // CHECK-NEXT: tfsr_el12
 // CHECK:      invalid operand for instruction
 // CHECK-NEXT: tfsre0_el1
+// CHECK:      invalid operand for instruction
+// CHECK-NEXT: gmid_el1
 
 msr tco
 msr gcr_el1
@@ -608,6 +614,7 @@
 msr tfsr_el3
 msr tfsr_el12
 msr tfsre0_el1
+msr gmid_el1
 
 // CHECK:      too few operands for instruction
 // CHECK-NEXT: tco
@@ -625,6 +632,8 @@
 // CHECK-NEXT: tfsr_el12
 // CHECK:      too few operands for instruction
 // CHECK-NEXT: tfsre0_el1
+// CHECK:      expected writable system register or pstate
+// CHECK-NEXT: gmid_el1
 
 msr x0, tco
 msr x1, gcr_el1
@@ -634,6 +643,7 @@
 msr x5, tfsr_el3
 msr x6, tfsr_el12
 msr x7, tfsre0_el1
+msr x7, gmid_el1
 
 // CHECK:      expected writable system register or pstate
 // CHECK-NEXT: tco
@@ -651,6 +661,13 @@
 // CHECK-NEXT: tfsr_el12
 // CHECK:      expected writable system register or pstate
 // CHECK-NEXT: tfsre0_el1
+// CHECK:      expected writable system register or pstate
+// CHECK-NEXT: gmid_el1
+
+msr gmid_el1, x7
+
+// CHECK:      expected writable system register or pstate
+// CHECK-NEXT: gmid_el1
 
 // Among the system registers added by MTE, only TCO can be used with MSR (imm).
 // The rest can only be used with MSR (reg).
@@ -661,6 +678,8 @@
 msr tfsr_el3, #5
 msr tfsr_el12, #6
 msr tfsre0_el1, #7
+// Is read only
+msr gmid_el1, #7
 
 // CHECK:      invalid operand for instruction
 // CHECK-NEXT: gcr_el1
@@ -676,6 +695,8 @@
 // CHECK-NEXT: tfsr_el12
 // CHECK:      invalid operand for instruction
 // CHECK-NEXT: tfsre0_el1
+// CHECK:      expected writable system register or pstate
+// CHECK-NEXT: gmid_el1
 
 // Xd cannot be the stack pointer, the rest can
 subps sp, x0, x1
Index: test/MC/AArch64/armv8.5a-mte.s
===================================================================
--- test/MC/AArch64/armv8.5a-mte.s
+++ test/MC/AArch64/armv8.5a-mte.s
@@ -420,6 +420,7 @@
 mrs x5, tfsr_el3
 mrs x6, tfsr_el12
 mrs x7, tfsre0_el1
+mrs x7, gmid_el1
 
 // CHECK: mrs x0, TCO           // encoding: [0xe0,0x42,0x3b,0xd5]
 // CHECK: mrs x1, GCR_EL1       // encoding: [0xc1,0x10,0x38,0xd5]
@@ -429,6 +430,7 @@
 // CHECK: mrs x5, TFSR_EL3      // encoding: [0x05,0x66,0x3e,0xd5]
 // CHECK: mrs x6, TFSR_EL12     // encoding: [0x06,0x66,0x3d,0xd5]
 // CHECK: mrs x7, TFSRE0_EL1    // encoding: [0x27,0x66,0x38,0xd5]
+// CHECK: mrs x7, GMID_EL1      // encoding: [0x87,0x00,0x39,0xd5]
 
 // NOMTE: expected readable system register
 // NOMTE-NEXT: tco
@@ -446,6 +448,8 @@
 // NOMTE-NEXT: tfsr_el12
 // NOMTE: expected readable system register
 // NOMTE-NEXT: tfsre0_el1
+// NOMTE: expected readable system register
+// NOMTE-NEXT: gmid_el1
 
 msr tco, #0
 
Index: test/MC/Disassembler/AArch64/armv8.5a-mte.txt
===================================================================
--- test/MC/Disassembler/AArch64/armv8.5a-mte.txt
+++ test/MC/Disassembler/AArch64/armv8.5a-mte.txt
@@ -493,6 +493,7 @@
 [0x05,0x66,0x3e,0xd5]
 [0x06,0x66,0x3d,0xd5]
 [0x27,0x66,0x38,0xd5]
+[0x88,0x00,0x39,0xd5]
 
 # CHECK: mrs x0, TCO
 # CHECK: mrs x1, GCR_EL1
@@ -502,6 +503,7 @@
 # CHECK: mrs x5, TFSR_EL3
 # CHECK: mrs x6, TFSR_EL12
 # CHECK: mrs x7, TFSRE0_EL1
+# CHECK: mrs x8, GMID_EL1
 
 # NOMTE: mrs x0, S3_3_C4_C2_7
 # NOMTE: mrs x1, S3_0_C1_C0_6
@@ -511,6 +513,7 @@
 # NOMTE: mrs x5, S3_6_C6_C6_0
 # NOMTE: mrs x6, S3_5_C6_C6_0
 # NOMTE: mrs x7, S3_0_C6_C6_1
+# NOMTE: mrs x8, S3_1_C0_C0_4
 
 [0x9f,0x40,0x03,0xd5]
 
@@ -525,6 +528,7 @@
 [0x05,0x66,0x1e,0xd5]
 [0x06,0x66,0x1d,0xd5]
 [0x27,0x66,0x18,0xd5]
+[0x88,0x00,0x19,0xd5]
 
 # CHECK: msr TCO, x0
 # CHECK: msr GCR_EL1, x1
@@ -534,6 +538,8 @@
 # CHECK: msr TFSR_EL3, x5
 # CHECK: msr TFSR_EL12, x6
 # CHECK: msr TFSRE0_EL1, x7
+# GMID_EL1 is read only
+# CHECK: msr S3_1_C0_C0_4, x8
 
 # NOMTE: msr S3_3_C4_C2_7, x0
 # NOMTE: msr S3_0_C1_C0_6, x1
@@ -543,3 +549,4 @@
 # NOMTE: msr S3_6_C6_C6_0, x5
 # NOMTE: msr S3_5_C6_C6_0, x6
 # NOMTE: msr S3_0_C6_C6_1, x7
+# NOMTE: msr S3_1_C0_C0_4, x8