VMECID_A

This register is present only when FEAT_MEC is implemented. Otherwise, direct accesses to VMECID_A_EL2 are UNDEFINED.

Attributes

Field descriptions

Bits [63:16]

MECID, bits [15:0]

If MECIDWidth is less than 16 bits, bits[15:MECIDWidth] are RES0.

Note

MECIDWidth is defined in MECIDR_EL2.MECIDWidthm1.

The reset behavior of this field is:

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Accessing VMECID_A_EL2

Accesses to this register use the following encodings in the System register encoding space:

MRS <Xt>, VMECID_A_EL2

op0	op1	CRn	CRm	op2
0b11	0b100	0b1010	0b1001	0b001

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then UNDEFINED; elsif PSTATE.EL == EL2 then if !IsCurrentSecurityState(SS_Realm) then UNDEFINED; elsif HaveEL(EL3) && EL3SDDUndefPriority() && SCR_EL3.MECEn == '0' then UNDEFINED; elsif HaveEL(EL3) && SCR_EL3.MECEn == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else X[t, 64] = VMECID_A_EL2; elsif PSTATE.EL == EL3 then X[t, 64] = VMECID_A_EL2;

MSR VMECID_A_EL2, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b100	0b1010	0b1001	0b001

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then UNDEFINED; elsif PSTATE.EL == EL2 then if !IsCurrentSecurityState(SS_Realm) then UNDEFINED; elsif HaveEL(EL3) && EL3SDDUndefPriority() && SCR_EL3.MECEn == '0' then UNDEFINED; elsif HaveEL(EL3) && SCR_EL3.MECEn == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x18); else VMECID_A_EL2 = X[t, 64]; elsif PSTATE.EL == EL3 then VMECID_A_EL2 = X[t, 64];

63	62	61	60	59	58	57	56	55	54	53	52	51	50	49	48	47	46	45	44	43	42	41	40	39	38	37	36	35	34	33	32
31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0
RES0																MECID

VMECID_A_EL2, Alternate MECID for EL1&0 stage 2 translation regime

Purpose