303 lines
14 KiB
ReStructuredText
303 lines
14 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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===========================
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Hypercall Op-codes (hcalls)
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===========================
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Overview
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=========
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Virtualization on 64-bit Power Book3S Platforms is based on the PAPR
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specification [1]_ which describes the run-time environment for a guest
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operating system and how it should interact with the hypervisor for
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privileged operations. Currently there are two PAPR compliant hypervisors:
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- **IBM PowerVM (PHYP)**: IBM's proprietary hypervisor that supports AIX,
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IBM-i and Linux as supported guests (termed as Logical Partitions
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or LPARS). It supports the full PAPR specification.
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- **Qemu/KVM**: Supports PPC64 linux guests running on a PPC64 linux host.
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Though it only implements a subset of PAPR specification called LoPAPR [2]_.
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On PPC64 arch a guest kernel running on top of a PAPR hypervisor is called
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a *pSeries guest*. A pseries guest runs in a supervisor mode (HV=0) and must
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issue hypercalls to the hypervisor whenever it needs to perform an action
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that is hypervisor priviledged [3]_ or for other services managed by the
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hypervisor.
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Hence a Hypercall (hcall) is essentially a request by the pseries guest
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asking hypervisor to perform a privileged operation on behalf of the guest. The
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guest issues a with necessary input operands. The hypervisor after performing
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the privilege operation returns a status code and output operands back to the
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guest.
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HCALL ABI
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=========
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The ABI specification for a hcall between a pseries guest and PAPR hypervisor
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is covered in section 14.5.3 of ref [2]_. Switch to the Hypervisor context is
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done via the instruction **HVCS** that expects the Opcode for hcall is set in *r3*
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and any in-arguments for the hcall are provided in registers *r4-r12*. If values
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have to be passed through a memory buffer, the data stored in that buffer should be
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in Big-endian byte order.
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Once control returns back to the guest after hypervisor has serviced the
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'HVCS' instruction the return value of the hcall is available in *r3* and any
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out values are returned in registers *r4-r12*. Again like in case of in-arguments,
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any out values stored in a memory buffer will be in Big-endian byte order.
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Powerpc arch code provides convenient wrappers named **plpar_hcall_xxx** defined
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in a arch specific header [4]_ to issue hcalls from the linux kernel
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running as pseries guest.
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Register Conventions
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====================
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Any hcall should follow same register convention as described in section 2.2.1.1
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of "64-Bit ELF V2 ABI Specification: Power Architecture"[5]_. Table below
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summarizes these conventions:
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+----------+----------+-------------------------------------------+
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| Register |Volatile | Purpose |
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| Range |(Y/N) | |
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+==========+==========+===========================================+
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| r0 | Y | Optional-usage |
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+----------+----------+-------------------------------------------+
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| r1 | N | Stack Pointer |
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+----------+----------+-------------------------------------------+
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| r2 | N | TOC |
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+----------+----------+-------------------------------------------+
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| r3 | Y | hcall opcode/return value |
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+----------+----------+-------------------------------------------+
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| r4-r10 | Y | in and out values |
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+----------+----------+-------------------------------------------+
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| r11 | Y | Optional-usage/Environmental pointer |
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+----------+----------+-------------------------------------------+
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| r12 | Y | Optional-usage/Function entry address at |
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| | | global entry point |
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+----------+----------+-------------------------------------------+
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| r13 | N | Thread-Pointer |
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+----------+----------+-------------------------------------------+
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| r14-r31 | N | Local Variables |
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+----------+----------+-------------------------------------------+
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| LR | Y | Link Register |
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+----------+----------+-------------------------------------------+
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| CTR | Y | Loop Counter |
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+----------+----------+-------------------------------------------+
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| XER | Y | Fixed-point exception register. |
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+----------+----------+-------------------------------------------+
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| CR0-1 | Y | Condition register fields. |
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+----------+----------+-------------------------------------------+
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| CR2-4 | N | Condition register fields. |
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+----------+----------+-------------------------------------------+
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| CR5-7 | Y | Condition register fields. |
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+----------+----------+-------------------------------------------+
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| Others | N | |
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+----------+----------+-------------------------------------------+
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DRC & DRC Indexes
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=================
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::
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DR1 Guest
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+--+ +------------+ +---------+
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| | <----> | | | User |
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+--+ DRC1 | | DRC | Space |
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| PAPR | Index +---------+
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DR2 | Hypervisor | | |
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+--+ | | <-----> | Kernel |
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| | <----> | | Hcall | |
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+--+ DRC2 +------------+ +---------+
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PAPR hypervisor terms shared hardware resources like PCI devices, NVDIMMs etc
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available for use by LPARs as Dynamic Resource (DR). When a DR is allocated to
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an LPAR, PHYP creates a data-structure called Dynamic Resource Connector (DRC)
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to manage LPAR access. An LPAR refers to a DRC via an opaque 32-bit number
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called DRC-Index. The DRC-index value is provided to the LPAR via device-tree
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where its present as an attribute in the device tree node associated with the
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DR.
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HCALL Return-values
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===================
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After servicing the hcall, hypervisor sets the return-value in *r3* indicating
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success or failure of the hcall. In case of a failure an error code indicates
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the cause for error. These codes are defined and documented in arch specific
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header [4]_.
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In some cases a hcall can potentially take a long time and need to be issued
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multiple times in order to be completely serviced. These hcalls will usually
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accept an opaque value *continue-token* within there argument list and a
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return value of *H_CONTINUE* indicates that hypervisor hasn't still finished
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servicing the hcall yet.
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To make such hcalls the guest need to set *continue-token == 0* for the
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initial call and use the hypervisor returned value of *continue-token*
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for each subsequent hcall until hypervisor returns a non *H_CONTINUE*
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return value.
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HCALL Op-codes
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==============
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Below is a partial list of HCALLs that are supported by PHYP. For the
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corresponding opcode values please look into the arch specific header [4]_:
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**H_SCM_READ_METADATA**
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| Input: *drcIndex, offset, buffer-address, numBytesToRead*
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| Out: *numBytesRead*
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| Return Value: *H_Success, H_Parameter, H_P2, H_P3, H_Hardware*
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Given a DRC Index of an NVDIMM, read N-bytes from the metadata area
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associated with it, at a specified offset and copy it to provided buffer.
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The metadata area stores configuration information such as label information,
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bad-blocks etc. The metadata area is located out-of-band of NVDIMM storage
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area hence a separate access semantics is provided.
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**H_SCM_WRITE_METADATA**
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| Input: *drcIndex, offset, data, numBytesToWrite*
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| Out: *None*
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| Return Value: *H_Success, H_Parameter, H_P2, H_P4, H_Hardware*
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Given a DRC Index of an NVDIMM, write N-bytes to the metadata area
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associated with it, at the specified offset and from the provided buffer.
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**H_SCM_BIND_MEM**
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| Input: *drcIndex, startingScmBlockIndex, numScmBlocksToBind,*
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| *targetLogicalMemoryAddress, continue-token*
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| Out: *continue-token, targetLogicalMemoryAddress, numScmBlocksToBound*
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| Return Value: *H_Success, H_Parameter, H_P2, H_P3, H_P4, H_Overlap,*
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| *H_Too_Big, H_P5, H_Busy*
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Given a DRC-Index of an NVDIMM, map a continuous SCM blocks range
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*(startingScmBlockIndex, startingScmBlockIndex+numScmBlocksToBind)* to the guest
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at *targetLogicalMemoryAddress* within guest physical address space. In
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case *targetLogicalMemoryAddress == 0xFFFFFFFF_FFFFFFFF* then hypervisor
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assigns a target address to the guest. The HCALL can fail if the Guest has
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an active PTE entry to the SCM block being bound.
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**H_SCM_UNBIND_MEM**
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| Input: drcIndex, startingScmLogicalMemoryAddress, numScmBlocksToUnbind
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| Out: numScmBlocksUnbound
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| Return Value: *H_Success, H_Parameter, H_P2, H_P3, H_In_Use, H_Overlap,*
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| *H_Busy, H_LongBusyOrder1mSec, H_LongBusyOrder10mSec*
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Given a DRC-Index of an NVDimm, unmap *numScmBlocksToUnbind* SCM blocks starting
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at *startingScmLogicalMemoryAddress* from guest physical address space. The
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HCALL can fail if the Guest has an active PTE entry to the SCM block being
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unbound.
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**H_SCM_QUERY_BLOCK_MEM_BINDING**
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| Input: *drcIndex, scmBlockIndex*
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| Out: *Guest-Physical-Address*
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| Return Value: *H_Success, H_Parameter, H_P2, H_NotFound*
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Given a DRC-Index and an SCM Block index return the guest physical address to
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which the SCM block is mapped to.
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**H_SCM_QUERY_LOGICAL_MEM_BINDING**
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| Input: *Guest-Physical-Address*
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| Out: *drcIndex, scmBlockIndex*
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| Return Value: *H_Success, H_Parameter, H_P2, H_NotFound*
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Given a guest physical address return which DRC Index and SCM block is mapped
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to that address.
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**H_SCM_UNBIND_ALL**
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| Input: *scmTargetScope, drcIndex*
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| Out: *None*
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| Return Value: *H_Success, H_Parameter, H_P2, H_P3, H_In_Use, H_Busy,*
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| *H_LongBusyOrder1mSec, H_LongBusyOrder10mSec*
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Depending on the Target scope unmap all SCM blocks belonging to all NVDIMMs
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or all SCM blocks belonging to a single NVDIMM identified by its drcIndex
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from the LPAR memory.
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**H_SCM_HEALTH**
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| Input: drcIndex
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| Out: *health-bitmap (r4), health-bit-valid-bitmap (r5)*
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| Return Value: *H_Success, H_Parameter, H_Hardware*
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Given a DRC Index return the info on predictive failure and overall health of
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the PMEM device. The asserted bits in the health-bitmap indicate one or more states
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(described in table below) of the PMEM device and health-bit-valid-bitmap indicate
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which bits in health-bitmap are valid. The bits are reported in
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reverse bit ordering for example a value of 0xC400000000000000
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indicates bits 0, 1, and 5 are valid.
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Health Bitmap Flags:
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+------+-----------------------------------------------------------------------+
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| Bit | Definition |
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+======+=======================================================================+
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| 00 | PMEM device is unable to persist memory contents. |
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| | If the system is powered down, nothing will be saved. |
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+------+-----------------------------------------------------------------------+
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| 01 | PMEM device failed to persist memory contents. Either contents were |
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| | not saved successfully on power down or were not restored properly on |
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| | power up. |
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+------+-----------------------------------------------------------------------+
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| 02 | PMEM device contents are persisted from previous IPL. The data from |
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| | the last boot were successfully restored. |
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+------+-----------------------------------------------------------------------+
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| 03 | PMEM device contents are not persisted from previous IPL. There was no|
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| | data to restore from the last boot. |
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+------+-----------------------------------------------------------------------+
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| 04 | PMEM device memory life remaining is critically low |
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+------+-----------------------------------------------------------------------+
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| 05 | PMEM device will be garded off next IPL due to failure |
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+------+-----------------------------------------------------------------------+
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| 06 | PMEM device contents cannot persist due to current platform health |
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| | status. A hardware failure may prevent data from being saved or |
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| | restored. |
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+------+-----------------------------------------------------------------------+
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| 07 | PMEM device is unable to persist memory contents in certain conditions|
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+------+-----------------------------------------------------------------------+
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| 08 | PMEM device is encrypted |
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+------+-----------------------------------------------------------------------+
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| 09 | PMEM device has successfully completed a requested erase or secure |
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| | erase procedure. |
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+------+-----------------------------------------------------------------------+
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|10:63 | Reserved / Unused |
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+------+-----------------------------------------------------------------------+
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**H_SCM_PERFORMANCE_STATS**
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| Input: drcIndex, resultBuffer Addr
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| Out: None
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| Return Value: *H_Success, H_Parameter, H_Unsupported, H_Hardware, H_Authority, H_Privilege*
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Given a DRC Index collect the performance statistics for NVDIMM and copy them
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to the resultBuffer.
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**H_SCM_FLUSH**
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| Input: *drcIndex, continue-token*
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| Out: *continue-token*
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| Return Value: *H_SUCCESS, H_Parameter, H_P2, H_BUSY*
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Given a DRC Index Flush the data to backend NVDIMM device.
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The hcall returns H_BUSY when the flush takes longer time and the hcall needs
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to be issued multiple times in order to be completely serviced. The
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*continue-token* from the output to be passed in the argument list of
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subsequent hcalls to the hypervisor until the hcall is completely serviced
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at which point H_SUCCESS or other error is returned by the hypervisor.
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References
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==========
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.. [1] "Power Architecture Platform Reference"
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https://en.wikipedia.org/wiki/Power_Architecture_Platform_Reference
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.. [2] "Linux on Power Architecture Platform Reference"
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https://members.openpowerfoundation.org/document/dl/469
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.. [3] "Definitions and Notation" Book III-Section 14.5.3
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https://openpowerfoundation.org/?resource_lib=power-isa-version-3-0
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.. [4] arch/powerpc/include/asm/hvcall.h
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.. [5] "64-Bit ELF V2 ABI Specification: Power Architecture"
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https://openpowerfoundation.org/?resource_lib=64-bit-elf-v2-abi-specification-power-architecture
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