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

Requirement

H

Defining extensions

H

Hypervisor

CSR Address

0x600

Length

* 32 when CSR[mstatus].SXL == 0 * 64 when CSR[mstatus].SXL == 1

Privilege Mode

S

Format

This CSR format changes dynamically.

hstatus Format when CSR[mstatus].SXL == 0
Figure 1. hstatus Format when CSR[mstatus].SXL == 0
hstatus Format when CSR[mstatus].SXL == 1
Figure 2. hstatus Format when CSR[mstatus].SXL == 1

Field Summary

Name Location Type Reset Value

hstatus.VSXL

33:32

[when,"($array_size(VSXLEN) == 1)"] RO [when,"($array_size(VSXLEN) != 1)"] RW

UNDEFINED_LEGAL

hstatus.VTSR

22

RW

UNDEFINED_LEGAL

hstatus.VTW

21

RW

UNDEFINED_LEGAL

hstatus.VTVM

20

RW

UNDEFINED_LEGAL

hstatus.VGEIN

17:12

[when,"(NUM_EXTERNAL_GUEST_INTERRUPTS == 63)"] RW [when,"(NUM_EXTERNAL_GUEST_INTERRUPTS != 63)"] RW-R

UNDEFINED_LEGAL

hstatus.HU

9

RW

UNDEFINED_LEGAL

hstatus.SPVP

8

RW

UNDEFINED_LEGAL

hstatus.SPV

7

RW

UNDEFINED_LEGAL

hstatus.GVA

6

RW

UNDEFINED_LEGAL

hstatus.VSBE

5

[when,"(VS_MODE_ENDIANNESS == "dynamic")"] RW [when,"(VS_MODE_ENDIANNESS != "dynamic")"] RO

UNDEFINED_LEGAL

Fields

VSXL

Location

33:32

Description

When return $array_size(VSXLEN) > 1;

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

Value VSXLEN

0

32

1

64

When return $array_size(VSXLEN) == 1 && $array_includes?(VSXLEN, 32);

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

When return $array_size(VSXLEN) == 1 && $array_includes?(VSXLEN, 64);

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

Type

RO

RW

Reset value

UNDEFINED_LEGAL

VTSR

Location

22

Description

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

Reset value

UNDEFINED_LEGAL

VTW

Location

21

Description

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
Type

RW

Reset value

UNDEFINED_LEGAL

VTVM

Location

20

Description

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

Reset value

UNDEFINED_LEGAL

VGEIN

Location

17:12

Description

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

RW-R

Reset value

UNDEFINED_LEGAL

HU

Location

9

Description

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

Reset value

UNDEFINED_LEGAL

SPVP

Location

8

Description

Written by hardware:

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

    Reset value

    UNDEFINED_LEGAL

SPV

Location

7

Description

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

    Reset value

    UNDEFINED_LEGAL

GVA

Location

6

Description

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

Reset value

UNDEFINED_LEGAL

VSBE

Location

5

Description

When return VS_MODE_ENDIANNESS == "little";

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

When return VS_MODE_ENDIANNESS == "big";

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

Type

RW

RO

Reset value

UNDEFINED_LEGAL

Software write

This CSR may store a value that is different from what software attempts to write.

When a software write occurs (e.g., through csrrw), the following determines the written value:

VSXL = if (CSR[mstatus].SXL < csr_value.VSXL) {
  # cannot set VSXLEN less than SXLEN
  return UNDEFINED_LEGAL_DETERMINISTIC;
} else if ((csr_value.VSXL & 0b10) != 0) {
  # MSB of VSXL represents XLEN > 64, which isn't legal
  return UNDEFINED_LEGAL_DETERMINISTIC;
} else {
  return csr_value.VSXL;
}

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

HU = csr_value.HU
SPVP = csr_value.SPVP
SPV = csr_value.SPV
GVA = csr_value.GVA
VSBE = csr_value.VSBE