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GICH_VMCR, Virtual Machine Control Register

The GICH_VMCR characteristics are:

Purpose

Enables the hypervisor to save and restore the virtual machine view of the GIC state. This register is updated when a virtual machine updates the virtual CPU interface registers.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

This register is available when the GIC implementation supports interrupt virtualization.

Attributes

GICH_VMCR is a 32-bit register.

Field descriptions

The GICH_VMCR bit assignments are:

313029282726252423222120191817161514131211109876543210
VPMRVBPR0VBPR1RES0VEOIMRES0VCBPRVFIQEnVAckCtlVENG1VENG0

VPMR, bits [31:24]

Virtual priority mask. The priority mask level for the CPU interface. If the priority of an interrupt is higher than the value indicated by this field, the interface signals the interrupt to the PE.

This alias field is updated when a VM updates GICV_PMR.Priority.

This field resets to an architecturally UNKNOWN value.

VBPR0, bits [23:21]

Virtual Binary Point Register, Group 0. Defines the point at which the priority value fields split into two parts, the Group priority field and the subpriority field. The Group priority field determines Group 0 interrupt preemption, and also determines Group 1 interrupt preemption if GICH_VMCR.VCBPR == 1.

This alias field is updated when a VM updates GICV_BPR.Binary_Point.

This field resets to an architecturally UNKNOWN value.

VBPR1, bits [20:18]

Virtual Binary Point Register, Group 1. Defines the point at which the priority value fields split into two parts, the Group priority field and the subpriority field. The Group priority field determines Group 1 interrupt preemption if GICH_VMCR.VCBPR == 0.

This alias field is updated when a VM updates GICV_ABPR.Binary_Point.

This field resets to an architecturally UNKNOWN value.

Bits [17:10]

Reserved, RES0.

VEOIM, bit [9]

Virtual EOImode. Possible values of this bit are:

VEOIMMeaning
0b0

A write of an INTID to GICV_EOIR or GICV_AEOIR drops the priority of the interrupt with that INTID, and also deactivates that interrupt.

0b1

A write of an INTID to GICV_EOIR or GICV_AEOIR only drops the priority of the interrupt with that INTID. Software must write to GICV_DIR to deactivate the interrupt.

This alias field is updated when a VM updates GICV_CTLR.EOImode.

This field resets to an architecturally UNKNOWN value.

Bits [8:5]

Reserved, RES0.

VCBPR, bit [4]

Virtual Common Binary Point Register. Possible values of this bit are:

VCBPRMeaning
0b0

GICV_ABPR determines the preemption group for Group 1 interrupts.

0b1

GICV_BPR determines the preemption group for Group 1 interrupts.

This alias field is updated when a VM updates GICV_CTLR.CBPR.

This field resets to an architecturally UNKNOWN value.

VFIQEn, bit [3]

Virtual FIQ enable. Possible values of this bit are:

VFIQEnMeaning
0b0

Group 0 virtual interrupts are presented as virtual IRQs.

0b1

Group 0 virtual interrupts are presented as virtual FIQs.

This alias field is updated when a VM updates GICV_CTLR.FIQEn.

This field resets to an architecturally UNKNOWN value.

VAckCtl, bit [2]

Virtual AckCtl. Possible values of this bit are:

VAckCtlMeaning
0b0

If the highest priority pending interrupt is Group 1, a read of GICV_IAR or GICV_HPPIR returns an INTID of 1022.

0b1

If the highest priority pending interrupt is Group 1, a read of GICV_IAR or GICV_HPPIR returns the INTID of the corresponding interrupt.

This alias field is updated when a VM updates GICV_CTLR.AckCtl.

This field is supported for backwards compatibility with GICv2. Arm deprecates the use of this field.

This field resets to an architecturally UNKNOWN value.

VENG1, bit [1]

Virtual interrupt enable, Group 1. Possible values of this bit are:

VENG1Meaning
0b0

Group 1 virtual interrupts are disabled.

0b1

Group 1 virtual interrupts are enabled.

This alias field is updated when a VM updates GICV_CTLR.EnableGrp1.

This field resets to an architecturally UNKNOWN value.

VENG0, bit [0]

Virtual interrupt enable, Group 0. Possible values of this bit are:

VENG0Meaning
0b0

Group 0 virtual interrupts are disabled.

0b1

Group 0 virtual interrupts are enabled.

This alias field is updated when a VM updates GICV_CTLR.EnableGrp0.

This field resets to an architecturally UNKNOWN value.

Note

A List register is in the pending state only if the corresponding GICH_LR<n> value is 0b01, that is, pending. The active and pending state is not included.

Accessing the GICH_VMCR

This register is used only when System register access is not enabled. When System register access is enabled:

  • For AArch32 implementations, ICH_VMCR provides equivalent functionality.
  • For AArch64 implementations, ICH_VMCR_EL2 provides equivalent functionality.

GICH_VMCR can be accessed through the memory-mapped interfaces:

ComponentOffsetInstance
GIC Virtual interface control0x0008GICH_VMCR

This interface is accessible as follows:

  • When GICD_CTLR.DS == 0b0 accesses to this register are RW.
  • When IsAccessSecure() accesses to this register are RW.
  • When !IsAccessSecure() accesses to this register are RW.


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