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