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GICH_HCR, Hypervisor Control Register

The GICH_HCR characteristics are:

Purpose

Controls the virtual CPU interface.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

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

Attributes

GICH_HCR is a 32-bit register.

Field descriptions

The GICH_HCR bit assignments are:

313029282726252423222120191817161514131211109876543210
EOICountRES0VGrp1DIEVGrp1EIEVGrp0DIEVGrp0EIENPIELRENPIEUIEEn

EOICount, bits [31:27]

Counts the number of EOIs received that do not have a corresponding entry in the List registers. The virtual CPU interface increments this field automatically when a matching EOI is received. EOIs that do not clear a bit in GICH_APR<n> do not cause an increment. If an EOI occurs when the value of this field is 31, then the field wraps to 0.

The maintenance interrupt is asserted whenever this field is nonzero and GICH_HCR.LRENPIE == 1.

This field resets to an architecturally UNKNOWN value.

Bits [26:8]

Reserved, RES0.

VGrp1DIE, bit [7]

VM Group 1 Disabled Interrupt Enable.

Enables the signaling of a maintenance interrupt while signaling of Group 1 interrupts from the virtual CPU interface to the connected virtual machine is disabled:

VGrp1DIEMeaning
0b0

Maintenance interrupt disabled.

0b1

Maintenance interrupt signaled when GICV_CTLR.EnableGrp1 == 0.

This field resets to an architecturally UNKNOWN value.

VGrp1EIE, bit [6]

VM Group 1 Enabled Interrupt Enable.

Enables the signaling of a maintenance interrupt while signaling of Group 1 interrupts from the virtual CPU interface to the connected virtual machine is enabled:

VGrp1EIEMeaning
0b0

Maintenance interrupt disabled.

0b1

Maintenance interrupt signaled when GICV_CTLR.EnableGrp1 == 1.

This field resets to an architecturally UNKNOWN value.

VGrp0DIE, bit [5]

VM Group 0 Disabled Interrupt Enable.

Enables the signaling of a maintenance interrupt while signaling of Group 0 interrupts from the virtual CPU interface to the connected virtual machine is disabled:

VGrp0DIEMeaning
0b0

Maintenance interrupt disabled.

0b1

Maintenance interrupt signaled when GICV_CTLR.EnableGrp0 == 0.

This field resets to an architecturally UNKNOWN value.

VGrp0EIE, bit [4]

VM Group 0 Enabled Interrupt Enable.

Enables the signaling of a maintenance interrupt while signaling of Group 0 interrupts from the virtual CPU interface to the connected virtual machine is enabled:

VGrp0EIEMeaning
0b0

Maintenance interrupt disabled.

0b1

Maintenance interrupt signaled when GICV_CTLR.EnableGrp0 == 1.

This field resets to an architecturally UNKNOWN value.

NPIE, bit [3]

No Pending Interrupt Enable.

Enables the signaling of a maintenance interrupt while no pending interrupts are present in the List registers:

NPIEMeaning
0b0

Maintenance interrupt disabled.

0b1

Maintenance interrupt signaled while the List registers contain no interrupts in the pending state.

This field resets to an architecturally UNKNOWN value.

LRENPIE, bit [2]

List Register Entry Not Present Interrupt Enable.

Enables the signaling of a maintenance interrupt while the virtual CPU interface does not have a corresponding valid List register for an EOI request:

LRENPIEMeaning
0b0

Maintenance interrupt disabled.

0b1

Maintenance interrupt signaled while GICH_HCR.EOICount is not 0.

This field resets to an architecturally UNKNOWN value.

UIE, bit [1]

Underflow Interrupt Enable.

Enables the signaling of a maintenance interrupt when the List registers are either empty or hold only one valid entry.

UIEMeaning
0b0

Maintenance interrupt disabled.

0b1

A maintenance interrupt is signaled if zero or one of the List register entries are marked as a valid interrupt.

This field resets to an architecturally UNKNOWN value.

En, bit [0]

Enable.

Global enable bit for the virtual CPU interface.

EnMeaning
0b0

Virtual CPU interface operation is disabled.

0b1

Virtual CPU interface operation is enabled.

When this field is 0:

  • The virtual CPU interface does not signal any maintenance interrupts.
  • The virtual CPU interface does not signal any virtual interrupts.
  • A read of GICV_IAR or GICV_AIAR returns a spurious interrupt ID.

This field resets to an architecturally UNKNOWN value.

The VGrp1DIE, VGrp1EIE, VGrp0DIE, and VGrp0EIE fields permit the hypervisor to track the virtual CPU interfaces that are enabled. The hypervisor can then route interrupts that have multiple targets correctly and efficiently, without having to read the virtual CPU interface status.

See Maintenance interrupts and GICH_MISR for more information.

Accessing the GICH_HCR

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

  • For AArch32 implementations, ICH_HCR provides equivalent functionality.
  • For AArch64 implementations, ICH_HCR_EL2 provides equivalent functionality.

GICH_HCR.En must be set to 1 for any virtual or maintenance interrupt to be asserted.

GICH_HCR can be accessed through the memory-mapped interfaces:

ComponentOffsetInstance
GIC Virtual interface control0x0000GICH_HCR

This interface is accessible as follows:

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


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