hstatus

Hypervisor Status

The hstatus register tracks and controls a VS-mode guest.

Unlike fields in sstatus, which are all aliases of fields mstatus, bits in hstatus are independent bits and do not have aliases.

Attributes

CSR Address	0x600
Defining extension	H, version >= 0
Length	64-bit
Privilege Mode	S

CSR Address

0x600

Defining extension

H, version >= 0

Length

64-bit

Privilege Mode

Format

Figure 1. hstatus format

Field Summary

Name Location Type Reset Value

Name	Location	Type	Reset Value
`VSXL`	33:32	RO	1
`VTSR`	22	RW	UNDEFINED_LEGAL
`VTW`	21	RW	UNDEFINED_LEGAL
`VTVM`	20	RW	UNDEFINED_LEGAL
`VGEIN`	17:12	RW-R	UNDEFINED_LEGAL
`HU`	9	RW	UNDEFINED_LEGAL
`SPVP`	8	RW	UNDEFINED_LEGAL
`SPV`	7	RW	UNDEFINED_LEGAL
`GVA`	6	RW	UNDEFINED_LEGAL
`VSBE`	5	RO	0

VSXL

33:32

VTSR

UNDEFINED_LEGAL

VTW

UNDEFINED_LEGAL

VTVM

UNDEFINED_LEGAL

VGEIN

17:12

RW-R

UNDEFINED_LEGAL

HU

UNDEFINED_LEGAL

SPVP

UNDEFINED_LEGAL

SPV

UNDEFINED_LEGAL

GVA

UNDEFINED_LEGAL

VSBE

Fields

`VSXL`

Location: hstatus[33:32]
Description: VS-mode XLen

Determines the effective XLEN in VS-mode. Valid values are:

Value

VSXLEN +

Because the implementation only supports a single VSXLEN == 32, this field is read-only-0.

Because the implementation only supports a single VSXLEN == 64, this field is read-only-1.

Type

RO	Read-Only Field has a hardwired value that does not change. Writes to an RO field are ignored.

Reset value

Software write

This field has special behavior when written by software (e.g., through csrrw).

When software tries to write csr_value, the field will be written with the return value of the function below.

if (CSR[mstatus].SXL < csr_value.VSXL) {
  return UNDEFINED_LEGAL_DETERMINISTIC;
} else if ((csr_value.VSXL) != 0) {
  return UNDEFINED_LEGAL_DETERMINISTIC;
} else {
  return csr_value.VSXL;
}

`VTSR`

Location: hstatus[22]
Description: Virtual Trap SRET

When hstatus.VTSR is set, executing the sret instruction in VS-mode raises a Virtual Instruction exception.

When hstatus.VTSR is clear, an sret instruction in VS-mode returns control to the mode stored in vsstatus.SPP.
Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`VTW`

Location

hstatus[21]

Description

Virtual Trap WFI

When hstatus.VTW is set, a wfi instruction executed in VS-mode raises a Virtual Instruction exception after waiting an implementation-defined amount of time (which can be 0).

When both hstatus.VTW and mstatus.TW are clear, a wfi instruction executes in VS-mode without a timeout period.

The wfi instruction is also affected by mstatus.TW, as shown below:

mstatus.TW	hstatus.VTW	wfi behavior
HS-mode	U-mode	VS-mode	VU-mode +
0	0	Wait	Trap (I)	Wait	Trap (V)
0	1	Wait	Trap (I)	Trap (V)	Trap (V)
1	-	Trap (I)	Trap (I)	Trap (I)	Trap (I) +
Trap (I) - Trap with `Illegal Instruction` code Trap (V) - Trap with `Virtual Instruction` code

mstatus.TW

hstatus.VTW

wfi behavior

HS-mode

U-mode

VS-mode

VU-mode +

Wait

Trap (I)

Wait

Trap (V)

Wait

Trap (I)

Trap (V)

Trap (I)

Trap (I) +

Trap (I) - Trap with Illegal Instruction code
Trap (V) - Trap with Virtual Instruction code

Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`VTVM`

Location: hstatus[20]
Description: Virtual Trap Virtual Memory

When set, a 'Virtual Instruction` trap occurs when executing an sfence.vma, sinval.vma, or an explicit CSR access of the satp (really vsatp) register when in VS-mode.

When clear, the instructions execute as normal in VS-mode.

Notably, hstatus.VTVM does not cause hfence.vvma, sfence.w.inval, or sfence.inval.ir to trap.

mstatus.TVM does not affect the VS-mode instructions controlled by hstatus.
Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`VGEIN`

Location: hstatus[17:12]
Description: Virtual Guest External Interrupt Number

Selects the guest external interrupt source for VS-level external interrupts.

When hstatus.VGEIN == 0, no external interrupt source is selected.

When hstatus.VGEIN != 0, it selects which bit of hgeip is currently active in VS-mode.
Type

RW-R	Read-Write Restricted Field is writable by software. Only certain values are legal. Writing an illegal value into the field is ignored, and the field retains its prior state.

Reset value

UNDEFINED_LEGAL

Software write

This field has special behavior when written by software (e.g., through csrrw).

When software tries to write csr_value, the field will be written with the return value of the function below.

if (csr_value.VGEIN <= NUM_EXTERNAL_GUEST_INTERRUPTS) {
  return csr_value.VGEIN;
} else {
  return ILLEGAL_WLRL;
}

`HU`

Location: hstatus[9]
Description: Hypervisor in U-mode

When set, the hypervisor load/store instructions (hlv, hlvx, and hsv) can be executed in U-mode.

When clear, the hypervisor load/store instructions cause an Illegal Instruction trap.
Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`SPVP`

Location

hstatus[8]

Description

Supervisor Previous Virtual Privilege

Written by hardware:

When taking a trap into HS-mode from VS-mode or VU-mode, hstatus.SPVP is written with the nominal privlege mode

Notably, unlike its analog mstatus.SPP, hstatus.SPVP is not cleared when returning from a trap.

Can also be written by software without immediate side-effect.

Affects execution by:
Controls the effective privilege level applied to the hypervisor load/store instructions, hlv, hlvx, and hsv.

Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`SPV`

Location

hstatus[7]

Description

Supervisor Previous Virtualization Mode

Written by hardware:

On a trap into HS-mode, hardware writes 1 when the prior mode was VS-mode or VU-mode, and 0 otherwise.

Can also be written by software without immediate side-effect.

Affects execution by:
When an sret instruction in executed in HS-mode or M-mode, control returns to VS-mode or VU-mode (as selected by mstatus.SPP) when hstatus.SPV is 1 and to HS-mode or U-mode otherwise.

Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`GVA`

Location

hstatus[6]

Description

Guest Virtual Address

Written by hardware whenever a trap is taken into HS-mode:

Writes 1 when a trap causes a guest virtual address to be written into stval (Breakpoint, * Address Misaligned, * Access Fault, * Page Fault, or * Guest-Page Fault).
Writes 0 otherwise

Does not affect execution.

Type

RW	Read-Write Field is writable by software. Any value that fits in the field is acceptable and shall be retained for subsequent reads.

Reset value: UNDEFINED_LEGAL

`VSBE`

Location: hstatus[5]
Description: VS-mode Big Endian

Controls the endianness of data VS-mode (0 = little, 1 = big). Instructions are always little endian, regardless of the data setting.

Since the CPU does not support big endian in VS-mode, this is hardwired to 0.

Since the CPU does not support litte endian in VS-mode, this is hardwired to 1.
Type

RO	Read-Only Field has a hardwired value that does not change. Writes to an RO field are ignored.

Reset value: 0