--- /dev/null
--- /dev/null
++.. SPDX-License-Identifier: GPL-2.0
++
++====================================
++Nested KVM on POWER
++====================================
++
++Introduction
++============
++
++This document explains how a guest operating system can act as a
++hypervisor and run nested guests through the use of hypercalls, if the
++hypervisor has implemented them. The terms L0, L1, and L2 are used to
++refer to different software entities. L0 is the hypervisor mode entity
++that would normally be called the "host" or "hypervisor". L1 is a
++guest virtual machine that is directly run under L0 and is initiated
++and controlled by L0. L2 is a guest virtual machine that is initiated
++and controlled by L1 acting as a hypervisor.
++
++Existing API
++============
++
++Linux/KVM has had support for Nesting as an L0 or L1 since 2018
++
++The L0 code was added::
++
++ commit 8e3f5fc1045dc49fd175b978c5457f5f51e7a2ce
++ Author: Paul Mackerras <paulus@ozlabs.org>
++ Date: Mon Oct 8 16:31:03 2018 +1100
++ KVM: PPC: Book3S HV: Framework and hcall stubs for nested virtualization
++
++The L1 code was added::
++
++ commit 360cae313702cdd0b90f82c261a8302fecef030a
++ Author: Paul Mackerras <paulus@ozlabs.org>
++ Date: Mon Oct 8 16:31:04 2018 +1100
++ KVM: PPC: Book3S HV: Nested guest entry via hypercall
++
++This API works primarily using a single hcall h_enter_nested(). This
++call made by the L1 to tell the L0 to start an L2 vCPU with the given
++state. The L0 then starts this L2 and runs until an L2 exit condition
++is reached. Once the L2 exits, the state of the L2 is given back to
++the L1 by the L0. The full L2 vCPU state is always transferred from
++and to L1 when the L2 is run. The L0 doesn't keep any state on the L2
++vCPU (except in the short sequence in the L0 on L1 -> L2 entry and L2
++-> L1 exit).
++
++The only state kept by the L0 is the partition table. The L1 registers
++it's partition table using the h_set_partition_table() hcall. All
++other state held by the L0 about the L2s is cached state (such as
++shadow page tables).
++
++The L1 may run any L2 or vCPU without first informing the L0. It
++simply starts the vCPU using h_enter_nested(). The creation of L2s and
++vCPUs is done implicitly whenever h_enter_nested() is called.
++
++In this document, we call this existing API the v1 API.
++
++New PAPR API
++===============
++
++The new PAPR API changes from the v1 API such that the creating L2 and
++associated vCPUs is explicit. In this document, we call this the v2
++API.
++
++h_enter_nested() is replaced with H_GUEST_VCPU_RUN(). Before this can
++be called the L1 must explicitly create the L2 using h_guest_create()
++and any associated vCPUs() created with h_guest_create_vCPU(). Getting
++and setting vCPU state can also be performed using h_guest_{g|s}et
++hcall.
++
++The basic execution flow is for an L1 to create an L2, run it, and
++delete it is:
++
++- L1 and L0 negotiate capabilities with H_GUEST_{G,S}ET_CAPABILITIES()
++ (normally at L1 boot time).
++
++- L1 requests the L0 create an L2 with H_GUEST_CREATE() and receives a token
++
++- L1 requests the L0 create an L2 vCPU with H_GUEST_CREATE_VCPU()
++
++- L1 and L0 communicate the vCPU state using the H_GUEST_{G,S}ET() hcall
++
++- L1 requests the L0 runs the vCPU running H_GUEST_VCPU_RUN() hcall
++
++- L1 deletes L2 with H_GUEST_DELETE()
++
++More details of the individual hcalls follows:
++
++HCALL Details
++=============
++
++This documentation is provided to give an overall understating of the
++API. It doesn't aim to provide all the details required to implement
++an L1 or L0. Latest version of PAPR can be referred to for more details.
++
++All these HCALLs are made by the L1 to the L0.
++
++H_GUEST_GET_CAPABILITIES()
++--------------------------
++
++This is called to get the capabilities of the L0 nested
++hypervisor. This includes capabilities such the CPU versions (eg
++POWER9, POWER10) that are supported as L2s::
++
++ H_GUEST_GET_CAPABILITIES(uint64 flags)
++
++ Parameters:
++ Input:
++ flags: Reserved
++ Output:
++ R3: Return code
++ R4: Hypervisor Supported Capabilities bitmap 1
++
++H_GUEST_SET_CAPABILITIES()
++--------------------------
++
++This is called to inform the L0 of the capabilities of the L1
++hypervisor. The set of flags passed here are the same as
++H_GUEST_GET_CAPABILITIES()
++
++Typically, GET will be called first and then SET will be called with a
++subset of the flags returned from GET. This process allows the L0 and
++L1 to negotiate an agreed set of capabilities::
++
++ H_GUEST_SET_CAPABILITIES(uint64 flags,
++ uint64 capabilitiesBitmap1)
++ Parameters:
++ Input:
++ flags: Reserved
++ capabilitiesBitmap1: Only capabilities advertised through
++ H_GUEST_GET_CAPABILITIES
++ Output:
++ R3: Return code
++ R4: If R3 = H_P2: The number of invalid bitmaps
++ R5: If R3 = H_P2: The index of first invalid bitmap
++
++H_GUEST_CREATE()
++----------------
++
++This is called to create an L2. A unique ID of the L2 created
++(similar to an LPID) is returned, which can be used on subsequent HCALLs to
++identify the L2::
++
++ H_GUEST_CREATE(uint64 flags,
++ uint64 continueToken);
++ Parameters:
++ Input:
++ flags: Reserved
++ continueToken: Initial call set to -1. Subsequent calls,
++ after H_Busy or H_LongBusyOrder has been
++ returned, value that was returned in R4.
++ Output:
++ R3: Return code. Notable:
++ H_Not_Enough_Resources: Unable to create Guest VCPU due to not
++ enough Hypervisor memory. See H_GUEST_CREATE_GET_STATE(flags =
++ takeOwnershipOfVcpuState)
++ R4: If R3 = H_Busy or_H_LongBusyOrder -> continueToken
++
++H_GUEST_CREATE_VCPU()
++---------------------
++
++This is called to create a vCPU associated with an L2. The L2 id
++(returned from H_GUEST_CREATE()) should be passed it. Also passed in
++is a unique (for this L2) vCPUid. This vCPUid is allocated by the
++L1::
++
++ H_GUEST_CREATE_VCPU(uint64 flags,
++ uint64 guestId,
++ uint64 vcpuId);
++ Parameters:
++ Input:
++ flags: Reserved
++ guestId: ID obtained from H_GUEST_CREATE
++ vcpuId: ID of the vCPU to be created. This must be within the
++ range of 0 to 2047
++ Output:
++ R3: Return code. Notable:
++ H_Not_Enough_Resources: Unable to create Guest VCPU due to not
++ enough Hypervisor memory. See H_GUEST_CREATE_GET_STATE(flags =
++ takeOwnershipOfVcpuState)
++
++H_GUEST_GET_STATE()
++-------------------
++
++This is called to get state associated with an L2 (Guest-wide or vCPU specific).
++This info is passed via the Guest State Buffer (GSB), a standard format as
++explained later in this doc, necessary details below:
++
++This can get either L2 wide or vcpu specific information. Examples of
++L2 wide is the timebase offset or process scoped page table
++info. Examples of vCPU specific are GPRs or VSRs. A bit in the flags
++parameter specifies if this call is L2 wide or vCPU specific and the
++IDs in the GSB must match this.
++
++The L1 provides a pointer to the GSB as a parameter to this call. Also
++provided is the L2 and vCPU IDs associated with the state to set.
++
++The L1 writes only the IDs and sizes in the GSB. L0 writes the
++associated values for each ID in the GSB::
++
++ H_GUEST_GET_STATE(uint64 flags,
++ uint64 guestId,
++ uint64 vcpuId,
++ uint64 dataBuffer,
++ uint64 dataBufferSizeInBytes);
++ Parameters:
++ Input:
++ flags:
++ Bit 0: getGuestWideState: Request state of the Guest instead
++ of an individual VCPU.
++ Bit 1: takeOwnershipOfVcpuState Indicate the L1 is taking
++ over ownership of the VCPU state and that the L0 can free
++ the storage holding the state. The VCPU state will need to
++ be returned to the Hypervisor via H_GUEST_SET_STATE prior
++ to H_GUEST_RUN_VCPU being called for this VCPU. The data
++ returned in the dataBuffer is in a Hypervisor internal
++ format.
++ Bits 2-63: Reserved
++ guestId: ID obtained from H_GUEST_CREATE
++ vcpuId: ID of the vCPU pass to H_GUEST_CREATE_VCPU
++ dataBuffer: A L1 real address of the GSB.
++ If takeOwnershipOfVcpuState, size must be at least the size
++ returned by ID=0x0001
++ dataBufferSizeInBytes: Size of dataBuffer
++ Output:
++ R3: Return code
++ R4: If R3 = H_Invalid_Element_Id: The array index of the bad
++ element ID.
++ If R3 = H_Invalid_Element_Size: The array index of the bad
++ element size.
++ If R3 = H_Invalid_Element_Value: The array index of the bad
++ element value.
++
++H_GUEST_SET_STATE()
++-------------------
++
++This is called to set L2 wide or vCPU specific L2 state. This info is
++passed via the Guest State Buffer (GSB), necessary details below:
++
++This can set either L2 wide or vcpu specific information. Examples of
++L2 wide is the timebase offset or process scoped page table
++info. Examples of vCPU specific are GPRs or VSRs. A bit in the flags
++parameter specifies if this call is L2 wide or vCPU specific and the
++IDs in the GSB must match this.
++
++The L1 provides a pointer to the GSB as a parameter to this call. Also
++provided is the L2 and vCPU IDs associated with the state to set.
++
++The L1 writes all values in the GSB and the L0 only reads the GSB for
++this call::
++
++ H_GUEST_SET_STATE(uint64 flags,
++ uint64 guestId,
++ uint64 vcpuId,
++ uint64 dataBuffer,
++ uint64 dataBufferSizeInBytes);
++ Parameters:
++ Input:
++ flags:
++ Bit 0: getGuestWideState: Request state of the Guest instead
++ of an individual VCPU.
++ Bit 1: returnOwnershipOfVcpuState Return Guest VCPU state. See
++ GET_STATE takeOwnershipOfVcpuState
++ Bits 2-63: Reserved
++ guestId: ID obtained from H_GUEST_CREATE
++ vcpuId: ID of the vCPU pass to H_GUEST_CREATE_VCPU
++ dataBuffer: A L1 real address of the GSB.
++ If takeOwnershipOfVcpuState, size must be at least the size
++ returned by ID=0x0001
++ dataBufferSizeInBytes: Size of dataBuffer
++ Output:
++ R3: Return code
++ R4: If R3 = H_Invalid_Element_Id: The array index of the bad
++ element ID.
++ If R3 = H_Invalid_Element_Size: The array index of the bad
++ element size.
++ If R3 = H_Invalid_Element_Value: The array index of the bad
++ element value.
++
++H_GUEST_RUN_VCPU()
++------------------
++
++This is called to run an L2 vCPU. The L2 and vCPU IDs are passed in as
++parameters. The vCPU runs with the state set previously using
++H_GUEST_SET_STATE(). When the L2 exits, the L1 will resume from this
++hcall.
++
++This hcall also has associated input and output GSBs. Unlike
++H_GUEST_{S,G}ET_STATE(), these GSB pointers are not passed in as
++parameters to the hcall (This was done in the interest of
++performance). The locations of these GSBs must be preregistered using
++the H_GUEST_SET_STATE() call with ID 0x0c00 and 0x0c01 (see table
++below).
++
++The input GSB may contain only VCPU specific elements to be set. This
++GSB may also contain zero elements (ie 0 in the first 4 bytes of the
++GSB) if nothing needs to be set.
++
++On exit from the hcall, the output buffer is filled with elements
++determined by the L0. The reason for the exit is contained in GPR4 (ie
++NIP is put in GPR4). The elements returned depend on the exit
++type. For example, if the exit reason is the L2 doing a hcall (GPR4 =
++0xc00), then GPR3-12 are provided in the output GSB as this is the
++state likely needed to service the hcall. If additional state is
++needed, H_GUEST_GET_STATE() may be called by the L1.
++
++To synthesize interrupts in the L2, when calling H_GUEST_RUN_VCPU()
++the L1 may set a flag (as a hcall parameter) and the L0 will
++synthesize the interrupt in the L2. Alternatively, the L1 may
++synthesize the interrupt itself using H_GUEST_SET_STATE() or the
++H_GUEST_RUN_VCPU() input GSB to set the state appropriately::
++
++ H_GUEST_RUN_VCPU(uint64 flags,
++ uint64 guestId,
++ uint64 vcpuId,
++ uint64 dataBuffer,
++ uint64 dataBufferSizeInBytes);
++ Parameters:
++ Input:
++ flags:
++ Bit 0: generateExternalInterrupt: Generate an external interrupt
++ Bit 1: generatePrivilegedDoorbell: Generate a Privileged Doorbell
++ Bit 2: sendToSystemResetâ: Generate a System Reset Interrupt
++ Bits 3-63: Reserved
++ guestId: ID obtained from H_GUEST_CREATE
++ vcpuId: ID of the vCPU pass to H_GUEST_CREATE_VCPU
++ Output:
++ R3: Return code
++ R4: If R3 = H_Success: The reason L1 VCPU exited (ie. NIA)
++ 0x000: The VCPU stopped running for an unspecified reason. An
++ example of this is the Hypervisor stopping a VCPU running
++ due to an outstanding interrupt for the Host Partition.
++ 0x980: HDEC
++ 0xC00: HCALL
++ 0xE00: HDSI
++ 0xE20: HISI
++ 0xE40: HEA
++ 0xF80: HV Fac Unavail
++ If R3 = H_Invalid_Element_Id, H_Invalid_Element_Size, or
++ H_Invalid_Element_Value: R4 is offset of the invalid element
++ in the input buffer.
++
++H_GUEST_DELETE()
++----------------
++
++This is called to delete an L2. All associated vCPUs are also
++deleted. No specific vCPU delete call is provided.
++
++A flag may be provided to delete all guests. This is used to reset the
++L0 in the case of kdump/kexec::
++
++ H_GUEST_DELETE(uint64 flags,
++ uint64 guestId)
++ Parameters:
++ Input:
++ flags:
++ Bit 0: deleteAllGuests: deletes all guests
++ Bits 1-63: Reserved
++ guestId: ID obtained from H_GUEST_CREATE
++ Output:
++ R3: Return code
++
++Guest State Buffer
++==================
++
++The Guest State Buffer (GSB) is the main method of communicating state
++about the L2 between the L1 and L0 via H_GUEST_{G,S}ET() and
++H_GUEST_VCPU_RUN() calls.
++
++State may be associated with a whole L2 (eg timebase offset) or a
++specific L2 vCPU (eg. GPR state). Only L2 VCPU state maybe be set by
++H_GUEST_VCPU_RUN().
++
++All data in the GSB is big endian (as is standard in PAPR)
++
++The Guest state buffer has a header which gives the number of
++elements, followed by the GSB elements themselves.
++
++GSB header:
++
+++----------+----------+-------------------------------------------+
++| Offset | Size | Purpose |
++| Bytes | Bytes | |
+++==========+==========+===========================================+
++| 0 | 4 | Number of elements |
+++----------+----------+-------------------------------------------+
++| 4 | | Guest state buffer elements |
+++----------+----------+-------------------------------------------+
++
++GSB element:
++
+++----------+----------+-------------------------------------------+
++| Offset | Size | Purpose |
++| Bytes | Bytes | |
+++==========+==========+===========================================+
++| 0 | 2 | ID |
+++----------+----------+-------------------------------------------+
++| 2 | 2 | Size of Value |
+++----------+----------+-------------------------------------------+
++| 4 | As above | Value |
+++----------+----------+-------------------------------------------+
++
++The ID in the GSB element specifies what is to be set. This includes
++archtected state like GPRs, VSRs, SPRs, plus also some meta data about
++the partition like the timebase offset and partition scoped page
++table information.
++
+++--------+-------+----+--------+----------------------------------+
++| ID | Size | RW | Thread | Details |
++| | Bytes | | Guest | |
++| | | | Scope | |
+++========+=======+====+========+==================================+
++| 0x0000 | | RW | TG | NOP element |
+++--------+-------+----+--------+----------------------------------+
++| 0x0001 | 0x08 | R | G | Size of L0 vCPU state. See: |
++| | | | | H_GUEST_GET_STATE: |
++| | | | | flags = takeOwnershipOfVcpuState |
+++--------+-------+----+--------+----------------------------------+
++| 0x0002 | 0x08 | R | G | Size Run vCPU out buffer |
+++--------+-------+----+--------+----------------------------------+
++| 0x0003 | 0x04 | RW | G | Logical PVR |
+++--------+-------+----+--------+----------------------------------+
++| 0x0004 | 0x08 | RW | G | TB Offset (L1 relative) |
+++--------+-------+----+--------+----------------------------------+
++| 0x0005 | 0x18 | RW | G |Partition scoped page tbl info: |
++| | | | | |
++| | | | |- 0x00 Addr part scope table |
++| | | | |- 0x08 Num addr bits |
++| | | | |- 0x10 Size root dir |
+++--------+-------+----+--------+----------------------------------+
++| 0x0006 | 0x10 | RW | G |Process Table Information: |
++| | | | | |
++| | | | |- 0x0 Addr proc scope table |
++| | | | |- 0x8 Table size. |
+++--------+-------+----+--------+----------------------------------+
++| 0x0007-| | | | Reserved |
++| 0x0BFF | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x0C00 | 0x10 | RW | T |Run vCPU Input Buffer: |
++| | | | | |
++| | | | |- 0x0 Addr of buffer |
++| | | | |- 0x8 Buffer Size. |
+++--------+-------+----+--------+----------------------------------+
++| 0x0C01 | 0x10 | RW | T |Run vCPU Output Buffer: |
++| | | | | |
++| | | | |- 0x0 Addr of buffer |
++| | | | |- 0x8 Buffer Size. |
+++--------+-------+----+--------+----------------------------------+
++| 0x0C02 | 0x08 | RW | T | vCPU VPA Address |
+++--------+-------+----+--------+----------------------------------+
++| 0x0C03-| | | | Reserved |
++| 0x0FFF | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x1000-| 0x08 | RW | T | GPR 0-31 |
++| 0x101F | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x1020 | 0x08 | T | T | HDEC expiry TB |
+++--------+-------+----+--------+----------------------------------+
++| 0x1021 | 0x08 | RW | T | NIA |
+++--------+-------+----+--------+----------------------------------+
++| 0x1022 | 0x08 | RW | T | MSR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1023 | 0x08 | RW | T | LR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1024 | 0x08 | RW | T | XER |
+++--------+-------+----+--------+----------------------------------+
++| 0x1025 | 0x08 | RW | T | CTR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1026 | 0x08 | RW | T | CFAR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1027 | 0x08 | RW | T | SRR0 |
+++--------+-------+----+--------+----------------------------------+
++| 0x1028 | 0x08 | RW | T | SRR1 |
+++--------+-------+----+--------+----------------------------------+
++| 0x1029 | 0x08 | RW | T | DAR |
+++--------+-------+----+--------+----------------------------------+
++| 0x102A | 0x08 | RW | T | DEC expiry TB |
+++--------+-------+----+--------+----------------------------------+
++| 0x102B | 0x08 | RW | T | VTB |
+++--------+-------+----+--------+----------------------------------+
++| 0x102C | 0x08 | RW | T | LPCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x102D | 0x08 | RW | T | HFSCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x102E | 0x08 | RW | T | FSCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x102F | 0x08 | RW | T | FPSCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1030 | 0x08 | RW | T | DAWR0 |
+++--------+-------+----+--------+----------------------------------+
++| 0x1031 | 0x08 | RW | T | DAWR1 |
+++--------+-------+----+--------+----------------------------------+
++| 0x1032 | 0x08 | RW | T | CIABR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1033 | 0x08 | RW | T | PURR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1034 | 0x08 | RW | T | SPURR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1035 | 0x08 | RW | T | IC |
+++--------+-------+----+--------+----------------------------------+
++| 0x1036-| 0x08 | RW | T | SPRG 0-3 |
++| 0x1039 | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x103A | 0x08 | W | T | PPR |
+++--------+-------+----+--------+----------------------------------+
++| 0x103B | 0x08 | RW | T | MMCR 0-3 |
++| 0x103E | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x103F | 0x08 | RW | T | MMCRA |
+++--------+-------+----+--------+----------------------------------+
++| 0x1040 | 0x08 | RW | T | SIER |
+++--------+-------+----+--------+----------------------------------+
++| 0x1041 | 0x08 | RW | T | SIER 2 |
+++--------+-------+----+--------+----------------------------------+
++| 0x1042 | 0x08 | RW | T | SIER 3 |
+++--------+-------+----+--------+----------------------------------+
++| 0x1043 | 0x08 | RW | T | BESCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1044 | 0x08 | RW | T | EBBHR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1045 | 0x08 | RW | T | EBBRR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1046 | 0x08 | RW | T | AMR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1047 | 0x08 | RW | T | IAMR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1048 | 0x08 | RW | T | AMOR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1049 | 0x08 | RW | T | UAMOR |
+++--------+-------+----+--------+----------------------------------+
++| 0x104A | 0x08 | RW | T | SDAR |
+++--------+-------+----+--------+----------------------------------+
++| 0x104B | 0x08 | RW | T | SIAR |
+++--------+-------+----+--------+----------------------------------+
++| 0x104C | 0x08 | RW | T | DSCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x104D | 0x08 | RW | T | TAR |
+++--------+-------+----+--------+----------------------------------+
++| 0x104E | 0x08 | RW | T | DEXCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x104F | 0x08 | RW | T | HDEXCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1050 | 0x08 | RW | T | HASHKEYR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1051 | 0x08 | RW | T | HASHPKEYR |
+++--------+-------+----+--------+----------------------------------+
++| 0x1052 | 0x08 | RW | T | CTRL |
+++--------+-------+----+--------+----------------------------------+
++| 0x1053-| | | | Reserved |
++| 0x1FFF | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x2000 | 0x04 | RW | T | CR |
+++--------+-------+----+--------+----------------------------------+
++| 0x2001 | 0x04 | RW | T | PIDR |
+++--------+-------+----+--------+----------------------------------+
++| 0x2002 | 0x04 | RW | T | DSISR |
+++--------+-------+----+--------+----------------------------------+
++| 0x2003 | 0x04 | RW | T | VSCR |
+++--------+-------+----+--------+----------------------------------+
++| 0x2004 | 0x04 | RW | T | VRSAVE |
+++--------+-------+----+--------+----------------------------------+
++| 0x2005 | 0x04 | RW | T | DAWRX0 |
+++--------+-------+----+--------+----------------------------------+
++| 0x2006 | 0x04 | RW | T | DAWRX1 |
+++--------+-------+----+--------+----------------------------------+
++| 0x2007-| 0x04 | RW | T | PMC 1-6 |
++| 0x200c | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x200D | 0x04 | RW | T | WORT |
+++--------+-------+----+--------+----------------------------------+
++| 0x200E | 0x04 | RW | T | PSPB |
+++--------+-------+----+--------+----------------------------------+
++| 0x200F-| | | | Reserved |
++| 0x2FFF | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x3000-| 0x10 | RW | T | VSR 0-63 |
++| 0x303F | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0x3040-| | | | Reserved |
++| 0xEFFF | | | | |
+++--------+-------+----+--------+----------------------------------+
++| 0xF000 | 0x08 | R | T | HDAR |
+++--------+-------+----+--------+----------------------------------+
++| 0xF001 | 0x04 | R | T | HDSISR |
+++--------+-------+----+--------+----------------------------------+
++| 0xF002 | 0x04 | R | T | HEIR |
+++--------+-------+----+--------+----------------------------------+
++| 0xF003 | 0x08 | R | T | ASDR |
+++--------+-------+----+--------+----------------------------------+
++
++
++Miscellaneous info
++==================
++
++State not in ptregs/hvregs
++--------------------------
++
++In the v1 API, some state is not in the ptregs/hvstate. This includes
++the vector register and some SPRs. For the L1 to set this state for
++the L2, the L1 loads up these hardware registers before the
++h_enter_nested() call and the L0 ensures they end up as the L2 state
++(by not touching them).
++
++The v2 API removes this and explicitly sets this state via the GSB.
++
++L1 Implementation details: Caching state
++----------------------------------------
++
++In the v1 API, all state is sent from the L1 to the L0 and vice versa
++on every h_enter_nested() hcall. If the L0 is not currently running
++any L2s, the L0 has no state information about them. The only
++exception to this is the location of the partition table, registered
++via h_set_partition_table().
++
++The v2 API changes this so that the L0 retains the L2 state even when
++it's vCPUs are no longer running. This means that the L1 only needs to
++communicate with the L0 about L2 state when it needs to modify the L2
++state, or when it's value is out of date. This provides an opportunity
++for performance optimisation.
++
++When a vCPU exits from a H_GUEST_RUN_VCPU() call, the L1 internally
++marks all L2 state as invalid. This means that if the L1 wants to know
++the L2 state (say via a kvm_get_one_reg() call), it needs call
++H_GUEST_GET_STATE() to get that state. Once it's read, it's marked as
++valid in L1 until the L2 is run again.
++
++Also, when an L1 modifies L2 vcpu state, it doesn't need to write it
++to the L0 until that L2 vcpu runs again. Hence when the L1 updates
++state (say via a kvm_set_one_reg() call), it writes to an internal L1
++copy and only flushes this copy to the L0 when the L2 runs again via
++the H_GUEST_VCPU_RUN() input buffer.
++
++This lazy updating of state by the L1 avoids unnecessary
++H_GUEST_{G|S}ET_STATE() calls.
projects / mirror_ubuntu-kernels.git / commitdiff