Laurent Dufour <lduf...@linux.vnet.ibm.com> writes: > Le 27/08/2019 à 17:23, Vaibhav Jain a écrit : >> This doc patch provides an initial description of the hcall op-codes >> that are used by Linux kernel running as a guest (LPAR) on top of >> PowerVM or any other sPAPR compliant hyper-visor (e.g qemu). >> >> Apart from documenting the hcalls the doc-patch also provides a >> rudimentary overview of how hcall ABI, how they are issued with the >> Linux kernel and how information/control flows between the guest and >> hypervisor. >> >> Signed-off-by: Vaibhav Jain <vaib...@linux.ibm.com> > > Hi Vaibhav, > > Thanks for documenting this. > > Besides my few remarks below, please consider: > > Reviewed-by: Laurent Dufour <lduf...@linux.ibm.com> > >> --- >> Change-log: >> >> Initial version of this doc-patch was posted and reviewed as part of >> the patch-series "[PATCH v5 0/4] powerpc/papr_scm: Workaround for >> failure of drc bind after kexec" >> https://patchwork.ozlabs.org/patch/1136022/. Changes introduced on top >> the original patch: >> >> * Replaced the of term PHYP with Hypervisor to indicate both >> PowerVM/Qemu [Laurent] >> * Emphasized that In/Out arguments to hcalls are in Big-endian format >> [Laurent] >> * Fixed minor word repetition, spell issues and grammatical error >> [Michal, Mpe] >> * Replaced various variant of term 'hcall' with a single >> variant. [Mpe] >> * Changed the documentation format from txt to ReST. [Mpe] >> * Changed the name of documentation file to papr_hcalls.rst. [Mpe] >> * Updated the section describing privileged operation by hypervisor >> to be more accurate [Mpe]. >> * Fixed up mention of register notation used for describing >> hcalls. [Mpe] >> * s/NVDimm/NVDIMM [Mpe] >> * Added section on return values from hcall [Mpe] >> * Described H_CONTINUE return-value for long running hcalls. >> --- >> Documentation/powerpc/papr_hcalls.rst | 200 ++++++++++++++++++++++++++ >> 1 file changed, 200 insertions(+) >> create mode 100644 Documentation/powerpc/papr_hcalls.rst >> >> diff --git a/Documentation/powerpc/papr_hcalls.rst >> b/Documentation/powerpc/papr_hcalls.rst >> new file mode 100644 >> index 000000000000..7afc0310de29 >> --- /dev/null >> +++ b/Documentation/powerpc/papr_hcalls.rst >> @@ -0,0 +1,200 @@ >> +=========================== >> +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 > ^ hcall ? > >> +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* in >> +Big-endian byte order. > Indeed, register valuer are not byte ordered, only values passed through > buffer in memory are byte ordered. > > Should it be explicitly said that Big-endian order is only concerning data > stored in memory? > What about something like that: > "...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 are in Big-endian order."
Yes that would be better. I guess to be pedantic every structure passed in memory needs to be defined in PAPR and could have some arbitrary ordering, but in practice everything is big endian. cheers
