1=================================== 2pSeries family boards (``pseries``) 3=================================== 4 5The Power machine para-virtualized environment described by the Linux on Power 6Architecture Reference ([LoPAR]_) document is called pSeries. This environment 7is also known as sPAPR, System p guests, or simply Power Linux guests (although 8it is capable of running other operating systems, such as AIX). 9 10Even though pSeries is designed to behave as a guest environment, it is also 11capable of acting as a hypervisor OS, providing, on that role, nested 12virtualization capabilities. 13 14Supported devices 15================= 16 17 * Multi processor support for many Power processors generations: POWER7, 18 POWER7+, POWER8, POWER8NVL, POWER9, and Power10. Support for POWER5+ exists, 19 but its state is unknown. 20 * Interrupt Controller, XICS (POWER8) and XIVE (POWER9 and Power10) 21 * vPHB PCIe Host bridge. 22 * vscsi and vnet devices, compatible with the same devices available on a 23 PowerVM hypervisor with VIOS managing LPARs. 24 * Virtio based devices. 25 * PCIe device pass through. 26 27Missing devices 28=============== 29 30 * SPICE support. 31 32Firmware 33======== 34 35The pSeries platform in QEMU comes with 2 firmwares: 36 37`SLOF <https://github.com/aik/SLOF>`_ (Slimline Open Firmware) is an 38implementation of the `IEEE 1275-1994, Standard for Boot (Initialization 39Configuration) Firmware: Core Requirements and Practices 40<https://standards.ieee.org/standard/1275-1994.html>`_. 41 42SLOF performs bus scanning, PCI resource allocation, provides the client 43interface to boot from block devices and network. 44 45QEMU includes a prebuilt image of SLOF which is updated when a more recent 46version is required. 47 48VOF (Virtual Open Firmware) is a minimalistic firmware to work with 49``-machine pseries,x-vof=on``. When enabled, the firmware acts as a slim 50shim and QEMU implements parts of the IEEE 1275 Open Firmware interface. 51 52VOF does not have device drivers, does not do PCI resource allocation and 53relies on ``-kernel`` used with Linux kernels recent enough (v5.4+) 54to PCI resource assignment. It is ideal to use with petitboot. 55 56Booting via ``-kernel`` supports the following: 57 58+-------------------+-------------------+------------------+ 59| kernel | pseries,x-vof=off | pseries,x-vof=on | 60+===================+===================+==================+ 61| vmlinux BE | ✓ | ✓ | 62+-------------------+-------------------+------------------+ 63| vmlinux LE | ✓ | ✓ | 64+-------------------+-------------------+------------------+ 65| zImage.pseries BE | ✓¹ | ✓¹ | 66+-------------------+-------------------+------------------+ 67| zImage.pseries LE | ✓ | ✓ | 68+-------------------+-------------------+------------------+ 69 70¹ must set kernel-addr=0 71 72Build directions 73================ 74 75.. code-block:: bash 76 77 ./configure --target-list=ppc64-softmmu && make 78 79Running instructions 80==================== 81 82Someone can select the pSeries machine type by running QEMU with the following 83options: 84 85.. code-block:: bash 86 87 qemu-system-ppc64 -M pseries <other QEMU arguments> 88 89sPAPR devices 90============= 91 92The sPAPR specification defines a set of para-virtualized devices, which are 93also supported by the pSeries machine in QEMU and can be instantiated with the 94``-device`` option: 95 96* ``spapr-vlan`` : a virtual network interface. 97* ``spapr-vscsi`` : a virtual SCSI disk interface. 98* ``spapr-rng`` : a pseudo-device for passing random number generator data to the 99 guest (see the `H_RANDOM hypercall feature 100 <https://wiki.qemu.org/Features/HRandomHypercall>`_ for details). 101* ``spapr-vty``: a virtual teletype. 102* ``spapr-pci-host-bridge``: a PCI host bridge. 103* ``tpm-spapr``: a Trusted Platform Module (TPM). 104* ``spapr-tpm-proxy``: a TPM proxy. 105 106These are compatible with the devices historically available for use when 107running the IBM PowerVM hypervisor with LPARs. 108 109However, since these devices have originally been specified with another 110hypervisor and non-Linux guests in mind, you should use the virtio counterparts 111(virtio-net, virtio-blk/scsi and virtio-rng for instance) if possible instead, 112since they will most probably give you better performance with Linux guests in a 113QEMU environment. 114 115The pSeries machine in QEMU is always instantiated with the following devices: 116 117* A NVRAM device (``spapr-nvram``). 118* A virtual teletype (``spapr-vty``). 119* A PCI host bridge (``spapr-pci-host-bridge``). 120 121Hence, it is not needed to add them manually, unless you use the ``-nodefaults`` 122command line option in QEMU. 123 124In the case of the default ``spapr-nvram`` device, if someone wants to make the 125contents of the NVRAM device persistent, they will need to specify a PFLASH 126device when starting QEMU, i.e. either use 127``-drive if=pflash,file=<filename>,format=raw`` to set the default PFLASH 128device, or specify one with an ID 129(``-drive if=none,file=<filename>,format=raw,id=pfid``) and pass that ID to the 130NVRAM device with ``-global spapr-nvram.drive=pfid``. 131 132sPAPR specification 133------------------- 134 135The main source of documentation on the sPAPR standard is the [LoPAR]_ document. 136However, documentation specific to QEMU's implementation of the specification 137can also be found in QEMU documentation: 138 139.. toctree:: 140 :maxdepth: 1 141 142 ../../specs/ppc-spapr-hotplug.rst 143 ../../specs/ppc-spapr-hcalls.rst 144 ../../specs/ppc-spapr-numa.rst 145 ../../specs/ppc-spapr-uv-hcalls.rst 146 ../../specs/ppc-spapr-xive.rst 147 148Switching between the KVM-PR and KVM-HV kernel module 149===================================================== 150 151Currently, there are two implementations of KVM on Power, ``kvm_hv.ko`` and 152``kvm_pr.ko``. 153 154 155If a host supports both KVM modes, and both KVM kernel modules are loaded, it is 156possible to switch between the two modes with the ``kvm-type`` parameter: 157 158* Use ``qemu-system-ppc64 -M pseries,accel=kvm,kvm-type=PR`` to use the 159 ``kvm_pr.ko`` kernel module. 160* Use ``qemu-system-ppc64 -M pseries,accel=kvm,kvm-type=HV`` to use ``kvm_hv.ko`` 161 instead. 162 163KVM-PR 164------ 165 166KVM-PR uses the so-called **PR**\ oblem state of the PPC CPUs to run the guests, 167i.e. the virtual machine is run in user mode and all privileged instructions 168trap and have to be emulated by the host. That means you can run KVM-PR inside 169a pSeries guest (or a PowerVM LPAR for that matter), and that is where it has 170originated, as historically (prior to POWER7) it was not possible to run Linux 171on hypervisor mode on a Power processor (this function was restricted to 172PowerVM, the IBM proprietary hypervisor). 173 174Because all privileged instructions are trapped, guests that use a lot of 175privileged instructions run quite slow with KVM-PR. On the other hand, because 176of that, this kernel module can run on pretty much every PPC hardware, and is 177able to emulate a lot of guests CPUs. This module can even be used to run other 178PowerPC guests like an emulated PowerMac. 179 180As KVM-PR can be run inside a pSeries guest, it can also provide nested 181virtualization capabilities (i.e. running a guest from within a guest). 182 183It is important to notice that, as KVM-HV provides a much better execution 184performance, maintenance work has been much more focused on it in the past 185years. Maintenance for KVM-PR has been minimal. 186 187In order to run KVM-PR guests with POWER9 processors, someone will need to start 188QEMU with ``kernel_irqchip=off`` command line option. 189 190KVM-HV 191------ 192 193KVM-HV uses the hypervisor mode of more recent Power processors, that allow 194access to the bare metal hardware directly. Although POWER7 had this capability, 195it was only starting with POWER8 that this was officially supported by IBM. 196 197Originally, KVM-HV was only available when running on a PowerNV platform (a.k.a. 198Power bare metal). Although it runs on a PowerNV platform, it can only be used 199to start pSeries guests. As the pSeries guest doesn't have access to the 200hypervisor mode of the Power CPU, it wasn't possible to run KVM-HV on a guest. 201This limitation has been lifted, and now it is possible to run KVM-HV inside 202pSeries guests as well, making nested virtualization possible with KVM-HV. 203 204As KVM-HV has access to privileged instructions, guests that use a lot of these 205can run much faster than with KVM-PR. On the other hand, the guest CPU has to be 206of the same type as the host CPU this way, e.g. it is not possible to specify an 207embedded PPC CPU for the guest with KVM-HV. However, there is at least the 208possibility to run the guest in a backward-compatibility mode of the previous 209CPUs generations, e.g. you can run a POWER7 guest on a POWER8 host by using 210``-cpu POWER8,compat=power7`` as parameter to QEMU. 211 212Modules support 213=============== 214 215As noticed in the sections above, each module can run in a different 216environment. The following table shows with which environment each module can 217run. As long as you are in a supported environment, you can run KVM-PR or KVM-HV 218nested. Combinations not shown in the table are not available. 219 220+--------------+------------+------+-------------------+----------+--------+ 221| Platform | Host type | Bits | Page table format | KVM-HV | KVM-PR | 222+==============+============+======+===================+==========+========+ 223| PowerNV | bare metal | 32 | hash | no | yes | 224| | | +-------------------+----------+--------+ 225| | | | radix | N/A | N/A | 226| | +------+-------------------+----------+--------+ 227| | | 64 | hash | yes | yes | 228| | | +-------------------+----------+--------+ 229| | | | radix | yes | no | 230+--------------+------------+------+-------------------+----------+--------+ 231| pSeries [1]_ | PowerNV | 32 | hash | no | yes | 232| | | +-------------------+----------+--------+ 233| | | | radix | N/A | N/A | 234| | +------+-------------------+----------+--------+ 235| | | 64 | hash | no | yes | 236| | | +-------------------+----------+--------+ 237| | | | radix | yes [2]_ | no | 238| +------------+------+-------------------+----------+--------+ 239| | PowerVM | 32 | hash | no | yes | 240| | | +-------------------+----------+--------+ 241| | | | radix | N/A | N/A | 242| | +------+-------------------+----------+--------+ 243| | | 64 | hash | no | yes | 244| | | +-------------------+----------+--------+ 245| | | | radix [3]_ | no | yes | 246+--------------+------------+------+-------------------+----------+--------+ 247 248.. [1] On POWER9 DD2.1 processors, the page table format on the host and guest 249 must be the same. 250 251.. [2] KVM-HV cannot run nested on POWER8 machines. 252 253.. [3] Introduced on Power10 machines. 254 255 256.. _power-papr-protected-execution-facility-pef: 257 258POWER (PAPR) Protected Execution Facility (PEF) 259----------------------------------------------- 260 261Protected Execution Facility (PEF), also known as Secure Guest support 262is a feature found on IBM POWER9 and POWER10 processors. 263 264If a suitable firmware including an Ultravisor is installed, it adds 265an extra memory protection mode to the CPU. The ultravisor manages a 266pool of secure memory which cannot be accessed by the hypervisor. 267 268When this feature is enabled in QEMU, a guest can use ultracalls to 269enter "secure mode". This transfers most of its memory to secure 270memory, where it cannot be eavesdropped by a compromised hypervisor. 271 272Launching 273^^^^^^^^^ 274 275To launch a guest which will be permitted to enter PEF secure mode:: 276 277 $ qemu-system-ppc64 \ 278 -object pef-guest,id=pef0 \ 279 -machine confidential-guest-support=pef0 \ 280 ... 281 282Live Migration 283^^^^^^^^^^^^^^ 284 285Live migration is not yet implemented for PEF guests. For 286consistency, QEMU currently prevents migration if the PEF feature is 287enabled, whether or not the guest has actually entered secure mode. 288 289 290Maintainer contact information 291============================== 292 293Cédric Le Goater <clg@kaod.org> 294 295Daniel Henrique Barboza <danielhb413@gmail.com> 296 297.. [LoPAR] `Linux on Power Architecture Reference document (LoPAR) revision 298 2.9 <https://openpowerfoundation.org/wp-content/uploads/2020/07/LoPAR-20200812.pdf>`_. 299