VTTBR_EL2

Holds the base address of the translation table for the initial lookup for stage 2 of an address translation in the EL1&0 translation regime, and other information for this translation regime.

Configuration

AArch64 System register VTTBR_EL2 bits [63:0] are architecturally mapped to AArch32 System register VTTBR[63:0].

This register has no effect if EL2 is not enabled in the current Security state.

VTTBR_EL2 is a 128-bit register that can also be accessed as a 64-bit value. If it is accessed as a 64-bit register, accesses read and write bits [63:0] and do not modify bits [127:64].

Attributes

Field descriptions

When FEAT_D128 is implemented and VTCR_EL2.D128 == 1:

Bits [127:88]

BADDR, bits [87:80, 47:5]

Translation table base address:

Bits A[55:x] of the stage 2 translation table base address bits are in register bits[87:80, 47:x].
Bits A[(x-1):0] of the stage 2 translation table base address are zero.

Address bit x is the minimum address bit required to align the translation table to the size of the table. x is calculated based on LOG2(StartTableSize), as described in VMSAv9-128. The smallest permitted value of x is 5.

The BADDR field is split as follows:

BADDR[50:43] is VTTBR_EL2[87:80].
BADDR[42:0] is VTTBR_EL2[47:5].

The reset behavior of this field is:

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

Bits [79:64]

VMID, bits [63:48]

VMID encoding when FEAT_VMID16 is implemented and VTCR_EL2.VS == 1

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
VMID

VMID, bits [15:0]

The VMID for the translation table.

If the implementation has an 8-bit VMID, bits [15:8] of this field are RES0.

The reset behavior of this field is:

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

VMID encoding when FEAT_VMID16 is not implemented or VTCR_EL2.VS == 0

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0								VMID

Bits [15:8]

Reserved, RES0.

VMID, bits [7:0]

The VMID for the translation table.

The VMID is 8 bits when any of the following are true:

EL2 is using AArch32.
VTCR_EL2.VS is 0.
FEAT_VMID16 is not implemented.

The reset behavior of this field is:

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

Bits [4:3]

SKL, bits [2:1]

Skip Level. Skip Level determines the number of levels to be skipped from the regular start level of the Non-Secure stage 2 translation table walk.

SKL	Meaning
0b00	Skip 0 level from the regular start level.
0b01	Skip 1 level from the regular start level.
0b10	Skip 2 levels from the regular start level.
0b11	Skip 3 levels from the regular start level.

The reset behavior of this field is:

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

CnP, bit [0]
When FEAT_TTCNP is implemented:

Common not Private. This bit indicates whether each entry that is pointed to by VTTBR_EL2 is a member of a common set that can be used by every PE in the Inner Shareable domain for which the value of VTTBR_EL2.CnP is 1.

CnP	Meaning
0b0	The translation table entries pointed to by VTTBR_EL2 are permitted to differ from the entries for VTTBR_EL2 for other PEs in the Inner Shareable domain. This is not affected by the value of the current VMID.
0b1	The translation table entries pointed to by VTTBR_EL2 are the same as the translation table entries for every other PE in the Inner Shareable domain for which the value of VTTBR_EL2.CnP is 1 and the VMID is the same as the current VMID.

This bit is permitted to be cached in a TLB.

Note

If the value of VTTBR_EL2.CnP bit is 1 on multiple PEs in the same Inner Shareable domain and those VTTBR_EL2s do not point to the same translation table entries when using the current VMID then the results of translations using VTTBR_EL2 are CONSTRAINED UNPREDICTABLE, see 'CONSTRAINED UNPREDICTABLE behaviors due to caching of control or data values'.

The reset behavior of this field is:

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

Otherwise:

When FEAT_D128 is not implemented or VTCR_EL2.D128 == 0:

VMID, bits [63:48]

VMID encoding when FEAT_VMID16 is implemented and VTCR_EL2.VS == 1

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
VMID

VMID, bits [15:0]

The VMID for the translation table.

If the implementation has an 8-bit VMID, bits [15:8] of this field are RES0.

The reset behavior of this field is:

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

VMID encoding when FEAT_VMID16 is not implemented or VTCR_EL2.VS == 0

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
RES0								VMID

Bits [15:8]

Reserved, RES0.

VMID, bits [7:0]

The VMID for the translation table.

The VMID is 8 bits when any of the following are true:

EL2 is using AArch32.
VTCR_EL2.VS is 0.
FEAT_VMID16 is not implemented.

The reset behavior of this field is:

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

BADDR, bits [47:1]

Translation table base address, A[47:x] or A[51:x], bits[47:1].

The BADDR field represents a 52-bit address if one of the following applies:

FEAT_LPA is implemented, the 64KB granule size is in use, and the value of VTCR_EL2.PS is 0b110.
FEAT_LPA2 is implemented, the 4KB or 16KB granule size is in use, and the Effective value of VTCR_EL2.DS is 1.
FEAT_D128 is implemented, 56-bit PAs are supported, the 64KB granule size is in use, and the value of VTCR_EL2.D128 is 0.

When VTTBR_EL2.BADDR represents a 52-bit addresses, all of the following apply:

Register bits[47:x] hold bits[47:x] of the stage 2 translation table base address, where x is determined by the size of the translation table at the start level.
The smallest permitted value of x is 6.
Register bits[5:2] hold bits[51:48] of the stage 2 translation table base address.
Bits[x:0] of the translation table base address are zero.
When x>6 register bits[(x-1):6] are RES0.
Register bit[1] is RES0.

Note

If BADDR represents a 52-bit address, and the translation table has fewer than eight entries, the table must be aligned to 64 bytes. Otherwise the translation table must be aligned to the size of the table.

For the 64KB granule, if FEAT_LPA is not implemented, and the value of VTCR_EL2.PS is 0b110, one the following IMPLEMENTATION DEFINED behaviors occur:

BADDR uses the extended format to represent a 52-bit base address.
BADDR does not use the extended format.

When the value of ID_AA64MMFR0_EL1.PARange indicates that the implementation supports a 56 bit PA size, bits [55:52] of the stage 2 translation table base address are zero.

If the Effective value of VTCR_EL2.PS is not 0b110 then:

Register bits[47:x] hold bits[47:x] of the stage 2 translation table base address.
Register bits[(x-1):1] are RES0.
If the implementation supports 52-bit PAs and IPAs then bits[51:48] of the translation table base addresses used in this stage of translation are 0b0000.

If any VTTBR_EL2[47:0] bit that is defined as RES0 has the value 1 when a translation table walk is performed using VTTBR_EL2, then the translation table base address might be misaligned, with effects that are CONSTRAINED UNPREDICTABLE, and must be one of the following:

Bits[x-1:0] of the translation table base address are treated as if all the bits are zero. The value read back from the corresponding register bits is either the value written to the register or zero.
The result of the calculation of an address for a translation table walk using this register can be corrupted in those bits that are nonzero.

The AArch64 Virtual Memory System Architecture chapter describes how x is calculated based on the value of VTCR_EL2.T0SZ, the stage of translation, and the translation granule size.

The reset behavior of this field is:

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

CnP, bit [0]
When FEAT_TTCNP is implemented:

CnP	Meaning
0b0	The translation table entries pointed to by VTTBR_EL2 are permitted to differ from the entries for VTTBR_EL2 for other PEs in the Inner Shareable domain. This is not affected by the value of the current VMID.
0b1	The translation table entries pointed to by VTTBR_EL2 are the same as the translation table entries for every other PE in the Inner Shareable domain for which the value of VTTBR_EL2.CnP is 1 and the VMID is the same as the current VMID.

This bit is permitted to be cached in a TLB.

Note

The reset behavior of this field is:

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

Otherwise:

Accessing VTTBR_EL2

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

MRS <Xt>, VTTBR_EL2

op0	op1	CRn	CRm	op2
0b11	0b100	0b0010	0b0001	0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then X[t, 64] = NVMem[0x020]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then X[t, 64] = VTTBR_EL2<63:0>; elsif PSTATE.EL == EL3 then X[t, 64] = VTTBR_EL2<63:0>;

MSR VTTBR_EL2, <Xt>

op0	op1	CRn	CRm	op2
0b11	0b100	0b0010	0b0001	0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then NVMem[0x020] = X[t, 64]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then VTTBR_EL2<63:0> = X[t, 64]; elsif PSTATE.EL == EL3 then VTTBR_EL2<63:0> = X[t, 64];

When FEAT_D128 is implemented

MRRS <Xt>, <Xt+1>, VTTBR_EL2

op0	op1	CRn	CRm	op2
0b11	0b100	0b0010	0b0001	0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then (X[t2, 64], X[t, 64]) = Split(NVMem[0x020, 128], 64); elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x14); else UNDEFINED; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && SCR_EL3.D128En == '0' then UNDEFINED; elsif HaveEL(EL3) && SCR_EL3.D128En == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x14); else (X[t2, 64], X[t, 64]) = Split(VTTBR_EL2, 64); elsif PSTATE.EL == EL3 then (X[t2, 64], X[t, 64]) = Split(VTTBR_EL2, 64);

When FEAT_D128 is implemented

MSRR VTTBR_EL2, <Xt>, <Xt+1>

op0	op1	CRn	CRm	op2
0b11	0b100	0b0010	0b0001	0b000

if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then NVMem[0x020, 128] = X[t2, 64]:X[t, 64]; elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64.SystemAccessTrap(EL2, 0x14); else UNDEFINED; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && EL3SDDUndefPriority() && SCR_EL3.D128En == '0' then UNDEFINED; elsif HaveEL(EL3) && SCR_EL3.D128En == '0' then if EL3SDDUndef() then UNDEFINED; else AArch64.SystemAccessTrap(EL3, 0x14); else VTTBR_EL2<127:0> = X[t2, 64]:X[t, 64]; elsif PSTATE.EL == EL3 then VTTBR_EL2<127:0> = X[t2, 64]:X[t, 64];

127	126	125	124	123	122	121	120	119	118	117	116	115	114	113	112	111	110	109	108	107	106	105	104	103	102	101	100	99	98	97	96
RES0
95	94	93	92	91	90	89	88	87	86	85	84	83	82	81	80	79	78	77	76	75	74	73	72	71	70	69	68	67	66	65	64
RES0								BADDR[50:43]								RES0
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
VMID																BADDR[42:0]
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
BADDR[42:0]																											RES0		SKL		CnP

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
VMID																BADDR
BADDR																															CnP

VTTBR_EL2, Virtualization Translation Table Base Register

Purpose

Configuration

Attributes

Field descriptions

When FEAT_D128 is implemented and VTCR_EL2.D128 == 1:

Bits [127:88]

BADDR, bits [87:80, 47:5]

Bits [79:64]

VMID, bits [63:48]

VMID encoding when FEAT_VMID16 is implemented and VTCR_EL2.VS == 1

VMID, bits [15:0]

VMID encoding when FEAT_VMID16 is not implemented or VTCR_EL2.VS == 0

Bits [15:8]

VMID, bits [7:0]

Bits [4:3]

SKL, bits [2:1]

CnP, bit [0]
When FEAT_TTCNP is implemented:

Otherwise:

When FEAT_D128 is not implemented or VTCR_EL2.D128 == 0:

VMID, bits [63:48]

VMID encoding when FEAT_VMID16 is implemented and VTCR_EL2.VS == 1

VMID, bits [15:0]

VMID encoding when FEAT_VMID16 is not implemented or VTCR_EL2.VS == 0

Bits [15:8]

VMID, bits [7:0]

BADDR, bits [47:1]

CnP, bit [0]
When FEAT_TTCNP is implemented:

Otherwise:

Accessing VTTBR_EL2

MRS <Xt>, VTTBR_EL2

MSR VTTBR_EL2, <Xt>

When FEAT_D128 is implemented

MRRS <Xt>, <Xt+1>, VTTBR_EL2

When FEAT_D128 is implemented

MSRR VTTBR_EL2, <Xt>, <Xt+1>

VTTBR_EL2, Virtualization Translation Table Base Register

Purpose

Configuration

Attributes

Field descriptions

When FEAT_D128 is implemented and VTCR_EL2.D128 == 1:

Bits [127:88]

BADDR, bits [87:80, 47:5]

Bits [79:64]

VMID, bits [63:48]

VMID encoding when FEAT_VMID16 is implemented and VTCR_EL2.VS == 1

VMID, bits [15:0]

VMID encoding when FEAT_VMID16 is not implemented or VTCR_EL2.VS == 0

Bits [15:8]

VMID, bits [7:0]

Bits [4:3]

SKL, bits [2:1]

CnP, bit [0]When FEAT_TTCNP is implemented:

Otherwise:

When FEAT_D128 is not implemented or VTCR_EL2.D128 == 0:

VMID, bits [63:48]

VMID encoding when FEAT_VMID16 is implemented and VTCR_EL2.VS == 1

VMID, bits [15:0]

VMID encoding when FEAT_VMID16 is not implemented or VTCR_EL2.VS == 0

Bits [15:8]

VMID, bits [7:0]

BADDR, bits [47:1]

CnP, bit [0]When FEAT_TTCNP is implemented:

Otherwise:

Accessing VTTBR_EL2

MRS <Xt>, VTTBR_EL2

MSR VTTBR_EL2, <Xt>

When FEAT_D128 is implemented

MRRS <Xt>, <Xt+1>, VTTBR_EL2

When FEAT_D128 is implemented

MSRR VTTBR_EL2, <Xt>, <Xt+1>

CnP, bit [0]
When FEAT_TTCNP is implemented:

CnP, bit [0]
When FEAT_TTCNP is implemented: