d55b123d14
Signed-off-by: Leonardo Garcia <lagarcia@br.ibm.com> Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com> Message-Id: <7f13e40e05ddb411697b0777b0e37757f76905e9.1638982486.git.lagarcia@br.ibm.com> Signed-off-by: Cédric Le Goater <clg@kaod.org>
101 lines
3.2 KiB
ReStructuredText
101 lines
3.2 KiB
ReStructuredText
sPAPR hypervisor calls
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----------------------
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When used with the ``pseries`` machine type, ``qemu-system-ppc64`` implements
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a set of hypervisor calls (a.k.a. hcalls) defined in the `Linux on Power
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Architecture Reference document (LoPAR)
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<https://cdn.openpowerfoundation.org/wp-content/uploads/2020/07/LoPAR-20200812.pdf>`_.
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This document is a subset of the Power Architecture Platform Reference (PAPR+)
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specification (IBM internal only), which is what PowerVM, the IBM proprietary
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hypervisor, adheres to.
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The subset in LoPAR is selected based on the requirements of Linux as a guest.
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In addition to those calls, we have added our own private hypervisor
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calls which are mostly used as a private interface between the firmware
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running in the guest and QEMU.
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All those hypercalls start at hcall number 0xf000 which correspond
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to an implementation specific range in PAPR.
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H_RTAS (0xf000)
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^^^^^^^^^^^^^^^
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RTAS stands for Run-Time Abstraction Sercies and is a set of runtime services
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generally provided by the firmware inside the guest to the operating system. It
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predates the existence of hypervisors (it was originally an extension to Open
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Firmware) and is still used by PAPR and LoPAR to provide various services that
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are not performance sensitive.
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We currently implement the RTAS services in QEMU itself. The actual RTAS
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"firmware" blob in the guest is a small stub of a few instructions which
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calls our private H_RTAS hypervisor call to pass the RTAS calls to QEMU.
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Arguments:
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``r3``: ``H_RTAS (0xf000)``
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``r4``: Guest physical address of RTAS parameter block.
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Returns:
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``H_SUCCESS``: Successfully called the RTAS function (RTAS result will have
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been stored in the parameter block).
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``H_PARAMETER``: Unknown token.
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H_LOGICAL_MEMOP (0xf001)
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^^^^^^^^^^^^^^^^^^^^^^^^
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When the guest runs in "real mode" (in powerpc terminology this means with MMU
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disabled, i.e. guest effective address equals to guest physical address), it
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only has access to a subset of memory and no I/Os.
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PAPR and LoPAR provides a set of hypervisor calls to perform cacheable or
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non-cacheable accesses to any guest physical addresses that the
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guest can use in order to access IO devices while in real mode.
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This is typically used by the firmware running in the guest.
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However, doing a hypercall for each access is extremely inefficient
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(even more so when running KVM) when accessing the frame buffer. In
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that case, things like scrolling become unusably slow.
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This hypercall allows the guest to request a "memory op" to be applied
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to memory. The supported memory ops at this point are to copy a range
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of memory (supports overlap of source and destination) and XOR which
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is used by our SLOF firmware to invert the screen.
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Arguments:
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``r3 ``: ``H_LOGICAL_MEMOP (0xf001)``
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``r4``: Guest physical address of destination.
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``r5``: Guest physical address of source.
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``r6``: Individual element size, defined by the binary logarithm of the
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desired size. Supported values are:
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``0`` = 1 byte
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``1`` = 2 bytes
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``2`` = 4 bytes
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``3`` = 8 bytes
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``r7``: Number of elements.
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``r8``: Operation. Supported values are:
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``0``: copy
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``1``: xor
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Returns:
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``H_SUCCESS``: Success.
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``H_PARAMETER``: Invalid argument.
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