The VTTBR_EL2 characteristics are:
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.
AArch64 System register VTTBR_EL2 bits [63:0] are architecturally mapped to AArch32 System register VTTBR[63:0].
If EL2 is not implemented, this register is RES0 from EL3.
This register has no effect if EL2 is not enabled in the current Security state.
VTTBR_EL2 is a 64-bit register.
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 |
15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
VMID |
The VMID for the translation table.
If EL2 is using AArch32, or if the implementation has an 8-bit VMID, this field is RES0.
The reset behavior of this field is:
15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
RES0 | VMID |
Reserved, RES0.
The VMID for the translation table.
The VMID is 8 bits when any of the following are true:
The reset behavior of this field is:
Translation table base address, A[47:x] or A[51:x], bits[47:1].
A translation table must be aligned to the size of the table, except that when using a translation table base address larger than 48 bits the minimum alignment of a table containing fewer than eight entries is 64 bytes.
In an implementation that includes FEAT_LPA, if the value of VTCR_EL2.PS is 0b110, then:
When the value of ID_AA64MMFR0_EL1.PARange indicates that the implementation does not support a 52 bit PA size, if a translation table lookup uses this register when the Effective value of VTCR_EL2.PS is 0b110 and the value of register bits[5:2] is nonzero, an Address size fault is generated.
If the Effective value of VTCR_EL2.PS is not 0b110 then:
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:
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:
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 field is permitted to be cached in a TLB.
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:
Reserved, RES0.
Accesses to this register use the following encodings in the System register encoding space:
op0 | op1 | CRn | CRm | op2 |
---|---|---|---|---|
0b11 | 0b100 | 0b0010 | 0b0001 | 0b000 |
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then return NVMem[0x020]; elsif EL2Enabled() && HCR_EL2.NV == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then return VTTBR_EL2; elsif PSTATE.EL == EL3 then return VTTBR_EL2;
op0 | op1 | CRn | CRm | op2 |
---|---|---|---|---|
0b11 | 0b100 | 0b0010 | 0b0001 | 0b000 |
if PSTATE.EL == EL0 then UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then NVMem[0x020] = X[t]; elsif EL2Enabled() && HCR_EL2.NV == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else UNDEFINED; elsif PSTATE.EL == EL2 then VTTBR_EL2 = X[t]; elsif PSTATE.EL == EL3 then VTTBR_EL2 = X[t];
20/09/2021 12:37; d4a233ffbdfb36e47856c443a7ce9a85f5e501ca
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