ID_AA64MMFR1

Provides information about the implemented memory model and memory management support in AArch64 state.

For general information about the interpretation of the ID registers, see 'Principles of the ID scheme for fields in ID registers'.

Configuration

Attributes

Field descriptions

ECBHB, bits [63:60]

Indicates support for restrictions on branch history speculation around exceptions. Defined values are:

ECBHB	Meaning
0b0000	The implementation does not disclose whether the branch history information created in a context before an exception to a higher Exception level using AArch64 can be used by code before that exception to exploitatively control the execution of any indirect branches in code in a different context after the exception.
0b0001	The branch history information created in a context before an exception to a higher Exception level using AArch64 cannot be used by code before that exception to exploitatively control the execution of any indirect branches in code in a different context after the exception.

All other values are reserved.

FEAT_ECBHB implements the functionality identified by the value 0b0001.

From Armv8.9, the value 0b0000 is not permitted.

CMOW, bits [59:56]

Indicates support for cache maintenance instruction permission. Defined values are:

CMOW	Meaning
0b0000	SCTLR_EL1.CMOW, SCTLR_EL2.CMOW, and HCRX_EL2.CMOW bits are not implemented.
0b0001	SCTLR_EL1.CMOW is implemented. If EL2 is implemented, SCTLR_EL2.CMOW and HCRX_EL2.CMOW bits are implemented.

All other values are reserved.

FEAT_CMOW implements the functionality identified by the value 0b0001.

From Armv8.8, the only permitted value is 0b0001.

TIDCP1, bits [55:52]

Indicates whether SCTLR_EL1.TIDCP and SCTLR_EL2.TIDCP are implemented in AArch64 state. Defined values are:

TIDCP1	Meaning
0b0000	SCTLR_EL1.TIDCP and SCTLR_EL2.TIDCP bits are not implemented and are RES0.
0b0001	SCTLR_EL1.TIDCP bit is implemented. If EL2 is implemented, SCTLR_EL2.TIDCP bit is implemented.

All other values are reserved.

FEAT_TIDCP1 implements the functionality identified by the value 0b0001.

From Armv8.8, the only permitted value is 0b0001.

nTLBPA, bits [51:48]

Indicates support for intermediate caching of translation table walks. Defined values are:

nTLBPA	Meaning
0b0000	The intermediate caching of translation table walks might include non-coherent physical translation caches.
0b0001	The intermediate caching of translation table walks does not include non-coherent physical translation caches.

Non-coherent physical translation caches are non-coherent caches of previous valid translation table entries since the last completed relevant TLBI applicable to the PE, where either:

The caching is indexed by the physical address of the location holding the translation table entry.
The caching is used for stage 1 translations and is indexed by the intermediate physical address of the location holding the translation table entry.

All other values are reserved.

FEAT_nTLBPA implements the functionality identified by the value 0b0001.

From Armv8.0, the permitted values are 0b0000 and 0b0001.

AFP, bits [47:44]

Indicates support for FPCR.{AH, FIZ, NEP}. Defined values are:

AFP	Meaning
0b0000	The FPCR.{AH, FIZ, NEP} fields are not supported.
0b0001	The FPCR.{AH, FIZ, NEP} fields are supported.

All other values are reserved.

FEAT_AFP implements the functionality identified by the value 0b0001.

From Armv8.7, if Advanced SIMD and floating-point is implemented, the only permitted value is 0b0001.

HCX, bits [43:40]

Indicates support for HCRX_EL2 and its associated EL3 trap. Defined values are:

HCX	Meaning
0b0000	HCRX_EL2 and its associated EL3 trap are not supported.
0b0001	HCRX_EL2 and its associated EL3 trap are supported.

All other values are reserved.

FEAT_HCX implements the functionality identified by the value 0b0001.

From Armv8.7, if EL2 is implemented, the only permitted value is 0b0001.

ETS, bits [39:36]

Indicates support for Enhanced Translation Synchronization. Defined values are:

ETS	Meaning
0b0000	Enhanced Translation Synchronization is not supported.
0b0001	Enhanced Translation Synchronization is not supported.
0b0010	Enhanced Translation Synchronization is supported

All other values are reserved.

FEAT_ETS2 implements the functionality identified by the value 0b0010.

From Armv8.7, the values 0b0000 and 0b0001 are not permitted.

TWED, bits [35:32]

Indicates support for the configurable delayed trapping of WFE. Defined values are:

TWED	Meaning
0b0000	Configurable delayed trapping of WFE is not supported.
0b0001	Configurable delayed trapping of WFE is supported.

All other values are reserved.

FEAT_TWED implements the functionality identified by the value 0b0001.

From Armv8.6, the permitted values are 0b0000 and 0b0001.

XNX, bits [31:28]

Indicates support for execute-never control distinction by Exception level at stage 2. Defined values are:

XNX	Meaning
0b0000	Distinction between EL0 and EL1 execute-never control at stage 2 not supported.
0b0001	Distinction between EL0 and EL1 execute-never control at stage 2 supported.

All other values are reserved.

FEAT_XNX implements the functionality identified by the value 0b0001.

From Armv8.2, the only permitted value is 0b0001.

SpecSEI, bits [27:24]
When FEAT_RAS is implemented:

Describes whether the PE can generate SError exceptions from speculative reads of memory, including speculative instruction fetches.

SpecSEI	Meaning
0b0000	The PE never generates an SError exception due to an External abort on a speculative read.
0b0001	The PE might generate an SError exception due to an External abort on a speculative read.

All other values are reserved.

Otherwise:

PAN, bits [23:20]

Privileged Access Never. Indicates support for the PAN bit in PSTATE, SPSR_EL1, SPSR_EL2, SPSR_EL3, and DSPSR_EL0. Defined values are:

PAN	Meaning
0b0000	PAN not supported.
0b0001	PAN supported.
0b0010	PAN supported and AT S1E1RP and AT S1E1WP instructions supported.
0b0011	PAN supported, AT S1E1RP and AT S1E1WP instructions supported, and SCTLR_EL1.EPAN and SCTLR_EL2.EPAN bits supported.

All other values are reserved.

FEAT_PAN implements the functionality identified by the value 0b0001.

FEAT_PAN2 implements the functionality added by the value 0b0010.

FEAT_PAN3 implements the functionality added by the value 0b0011.

In Armv8.1, the permitted values are 0b0001, 0b0010, and 0b0011.

From Armv8.2, the permitted values are 0b0010 and 0b0011.

From Armv8.7, the only permitted value is 0b0011.

LO, bits [19:16]

LORegions. Indicates support for LORegions. Defined values are:

LO	Meaning
0b0000	LORegions not supported.
0b0001	LORegions supported.

All other values are reserved.

FEAT_LOR implements the functionality identified by the value 0b0001.

From Armv8.1, the only permitted value is 0b0001.

HPDS, bits [15:12]

Hierarchical Permission Disables. Indicates support for disabling hierarchical controls in translation tables. Defined values are:

HPDS	Meaning
0b0000	Disabling of hierarchical controls not supported.
0b0001	Disabling of hierarchical controls supported with the TCR_EL1.{HPD1, HPD0}, TCR_EL2.HPD or TCR_EL2.{HPD1, HPD0}, and TCR_EL3.HPD bits.
0b0010	As for value 0b0001, and adds possible hardware allocation of bits[62:59] of the Translation table descriptors from the final lookup level for IMPLEMENTATION DEFINED use.

All other values are reserved.

FEAT_HPDS implements the functionality identified by the value 0b0001.

FEAT_HPDS2 implements the functionality identified by the value 0b0010.

From Armv8.1, the value 0b0000 is not permitted.

VH, bits [11:8]

Virtualization Host Extensions. Defined values are:

VH	Meaning
0b0000	Virtualization Host Extensions not supported.
0b0001	Virtualization Host Extensions supported.

All other values are reserved.

FEAT_VHE implements the functionality identified by the value 0b0001.

From Armv8.1, the only permitted value is 0b0001.

VMIDBits, bits [7:4]

Number of VMID bits. Defined values are:

VMIDBits	Meaning
0b0000	8 bits
0b0010	16 bits

All other values are reserved.

FEAT_VMID16 implements the functionality identified by the value 0b0010.

From Armv8.1, the permitted values are 0b0000 and 0b0010.

HAFDBS, bits [3:0]

Hardware updates to Access flag and Dirty state in translation tables. Defined values are:

HAFDBS	Meaning
0b0000	Hardware update of the Access flag and dirty state are not supported.
0b0001	Support for hardware update of the Access flag for Block and Page descriptors.
0b0010	As 0b0001, and adds support for hardware update of the Access flag for Block and Page descriptors. Hardware update of dirty state is supported.
0b0011	As 0b0010, and adds support for hardware update of the Access flag for Table descriptors.

All other values are reserved.

FEAT_HAFDBS implements the functionality identified by the values 0b0001 and 0b0010.

FEAT_HAFT implements the functionality identified by the value 0b0011.

Accessing ID_AA64MMFR1_EL1

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

MRS <Xt>, ID_AA64MMFR1_EL1

op0	op1	CRn	CRm	op2
0b11	0b000	0b0000	0b0111	0b001

if PSTATE.EL == EL0 then if IsFeatureImplemented(FEAT_IDST) then if EL2Enabled() && HCR_EL2.TGE == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else AArch64.SystemAccessTrap(EL1, 0x18); else UNDEFINED; elsif PSTATE.EL == EL1 then if EL2Enabled() && HCR_EL2.TID3 == '1' then AArch64.SystemAccessTrap(EL2, 0x18); else X[t, 64] = ID_AA64MMFR1_EL1; elsif PSTATE.EL == EL2 then X[t, 64] = ID_AA64MMFR1_EL1; elsif PSTATE.EL == EL3 then X[t, 64] = ID_AA64MMFR1_EL1;

ID_AA64MMFR1_EL1, AArch64 Memory Model Feature Register 1

Purpose

Configuration

Attributes

Field descriptions

ECBHB, bits [63:60]

CMOW, bits [59:56]

TIDCP1, bits [55:52]

nTLBPA, bits [51:48]

AFP, bits [47:44]

HCX, bits [43:40]

ETS, bits [39:36]

TWED, bits [35:32]

XNX, bits [31:28]

SpecSEI, bits [27:24]
When FEAT_RAS is implemented:

Otherwise:

PAN, bits [23:20]

LO, bits [19:16]

HPDS, bits [15:12]

VH, bits [11:8]

VMIDBits, bits [7:4]

HAFDBS, bits [3:0]

Accessing ID_AA64MMFR1_EL1

MRS <Xt>, ID_AA64MMFR1_EL1

ID_AA64MMFR1_EL1, AArch64 Memory Model Feature Register 1

Purpose

Configuration

Attributes

Field descriptions

ECBHB, bits [63:60]

CMOW, bits [59:56]

TIDCP1, bits [55:52]

nTLBPA, bits [51:48]

AFP, bits [47:44]

HCX, bits [43:40]

ETS, bits [39:36]

TWED, bits [35:32]

XNX, bits [31:28]

SpecSEI, bits [27:24]When FEAT_RAS is implemented:

Otherwise:

PAN, bits [23:20]

LO, bits [19:16]

HPDS, bits [15:12]

VH, bits [11:8]

VMIDBits, bits [7:4]

HAFDBS, bits [3:0]

Accessing ID_AA64MMFR1_EL1

MRS <Xt>, ID_AA64MMFR1_EL1

SpecSEI, bits [27:24]
When FEAT_RAS is implemented: