Commit Graph

191 Commits

Author SHA1 Message Date
John Baldwin
52ed569ba5 Remove unused openpic_devclass. 2022-05-10 10:21:38 -07:00
John Baldwin
03f6459cb3 ofw drivers: Remove unused devclass arguments to DRIVER_MODULE. 2022-05-09 14:26:44 -07:00
Stefan Eßer
e2650af157 Make CPU_SET macros compliant with other implementations
The introduction of <sched.h> improved compatibility with some 3rd
party software, but caused the configure scripts of some ports to
assume that they were run in a GLIBC compatible environment.

Parts of sched.h were made conditional on -D_WITH_CPU_SET_T being
added to ports, but there still were compatibility issues due to
invalid assumptions made in autoconfigure scripts.

The differences between the FreeBSD version of macros like CPU_AND,
CPU_OR, etc. and the GLIBC versions was in the number of arguments:
FreeBSD used a 2-address scheme (one source argument is also used as
the destination of the operation), while GLIBC uses a 3-adderess
scheme (2 source operands and a separately passed destination).

The GLIBC scheme provides a super-set of the functionality of the
FreeBSD macros, since it does not prevent passing the same variable
as source and destination arguments. In code that wanted to preserve
both source arguments, the FreeBSD macros required a temporary copy of
one of the source arguments.

This patch set allows to unconditionally provide functions and macros
expected by 3rd party software written for GLIBC based systems, but
breaks builds of externally maintained sources that use any of the
following macros: CPU_AND, CPU_ANDNOT, CPU_OR, CPU_XOR.

One contributed driver (contrib/ofed/libmlx5) has been patched to
support both the old and the new CPU_OR signatures. If this commit
is merged to -STABLE, the version test will have to be extended to
cover more ranges.

Ports that have added -D_WITH_CPU_SET_T to build on -CURRENT do
no longer require that option.

The FreeBSD version has been bumped to 1400046 to reflect this
incompatible change.

Reviewed by:	kib
MFC after:	2 weeks
Relnotes:	yes
Differential Revision:	https://reviews.freebsd.org/D33451
2021-12-30 12:20:32 +01:00
Warner Losh
c90902d39e bus_child_pnpinfo: fix two stragglers
ddfc9c4c59 was missing changes to two files to complete the
bus_child_pnpinfo_str->bus_child_pnpinfo. This fixes the broken kernel
builds.

Sponsored by:		Netflix
2021-06-22 22:10:31 -06:00
Warner Losh
ddfc9c4c59 newbus: Move from bus_child_{pnpinfo,location}_src to bus_child_{pnpinfo,location} with sbuf
Now that the upper layers all go through a layer to tie into these
information functions that translates an sbuf into char * and len. The
current interface suffers issues of what to do in cases of truncation,
etc. Instead, migrate all these functions to using struct sbuf and these
issues go away. The caller is also in charge of any memory allocation
and/or expansion that's needed during this process.

Create a bus_generic_child_{pnpinfo,location} and make it default. It
just returns success. This is for those busses that have no information
for these items. Migrate the now-empty routines to using this as
appropriate.

Document these new interfaces with man pages, and oversight from before.

Reviewed by:		jhb, bcr
Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D29937
2021-06-22 20:52:06 -06:00
Conrad Meyer
78599c32ef Add CFI start/end proc directives to arm64, i386, and ppc
Follow-up to r353959 and r368070: do the same for other architectures.

arm32 already seems to use its own .fnstart/.fnend directives, which
appear to be ARM-specific variants of the same thing.  Likewise, MIPS
uses .frame directives.

Reviewed by:	arichardson
Differential Revision:	https://reviews.freebsd.org/D27387
2020-12-05 00:33:28 +00:00
Brandon Bergren
d20d17f6d4 [PowerPC64LE] Fix RTAS LE calls in pseries.
Similar to OPAL calls, switch to big endian to do calls to RTAS.

(Missed this one when I was doing the bulk commit of PowerPC64LE support.)

Sponsored by:	Tag1 Consulting, Inc.
2020-09-23 04:09:02 +00:00
Brandon Bergren
4efb1ca7d2 [PowerPC64LE] Work around qemu TCG bug in mtmsrd emulation.
The TCG implementation of mtmsrd in qemu blindly copies the entire register
to the MSR, instead of the specific bit positions listed in the ISA.

This means that qemu will prematurely switch endian out from under the
running code instead of waiting for the rfid, causing an immediate trap
as it attempts to interpret the next instruction in the wrong endianness.

To work around this, ensure PSL_LE is still set before doing the mtmsrd.

In the future, we may wish to just turn off translation and unconditionally
use rfid to switch to the ofmsr instead of quasi-switching to the ofmsr.

Add a new platform option so this can be disabled. (And so that we can
conditonalize additional QEMU-specific hacks in the platform code.)

Sponsored by:	Tag1 Consulting, Inc.
2020-09-23 00:09:29 +00:00
Brandon Bergren
b49db8270a [PowerPC64LE] Fix endian dependence of ofw_real.c.
Since OFW always runs in big endian in practice, we need to convert several
bits back and forth.

This is necessary to communicate with SLOF on LE pseries.

Sponsored by:	Tag1 Consulting, Inc.
2020-09-22 23:59:02 +00:00
Brandon Bergren
a662559264 [PowerPC64LE] LE bringup work: locore / machdep / platform
This is the initial LE changes required in the machdep code to get as far
as platform attachment on qemu pseries.

Sponsored by:	Tag1 Consulting, Inc.
2020-09-22 23:55:34 +00:00
Mateusz Guzik
b64b31338f powerpc: clean up empty lines in .c and .h files 2020-09-01 21:20:08 +00:00
Brandon Bergren
9411e24df3 [PowerPC] kernel ifunc support for powerpc*, fix ppc64 relocation oddities.
This is a general cleanup of the relocatable kernel support on powerpc,
needed to enable kernel ifuncs.

 * Fix some relocatable issues in the kernel linker, and change to using
   a RELOCATABLE_KERNEL #define instead of #ifdef __powerpc__ for parts that
   other platforms can use in the future if they wish to have ET_DYN kernels.

 * Get rid of the DB_STOFFS hack now that the kernel is relocated to the DMAP
   properly across the board on powerpc64.

 * Add powerpc64 and powerpc32 ifunc functionality.

 * Allow AIM64 virtual mode OF kernels to run from the DMAP like other AIM64
   by implementing a virtual mode restart. This fixes the runtime address on
   PowerMac G5.

 * Fix symbol relocation problems on post-relocation kernels by relocating
   the symbol table.

 * Add an undocumented method for supplying kernel symbols on powernv and
   other powerpc machines using linux-style kernel/initrd loading -- If
   you pass the kernel in as the initrd as well, the copy resident in initrd
   will be used as a source for symbols when initializing the debugger.
   This method is subject to removal once we have a better way of doing this.

Approved by:	jhibbits
Relnotes:	yes
Sponsored by:	Tag1 Consulting, Inc.
Differential Revision:	https://reviews.freebsd.org/D23156
2020-05-07 19:32:49 +00:00
Pawel Biernacki
7029da5c36 Mark more nodes as CTLFLAG_MPSAFE or CTLFLAG_NEEDGIANT (17 of many)
r357614 added CTLFLAG_NEEDGIANT to make it easier to find nodes that are
still not MPSAFE (or already are but aren’t properly marked).
Use it in preparation for a general review of all nodes.

This is non-functional change that adds annotations to SYSCTL_NODE and
SYSCTL_PROC nodes using one of the soon-to-be-required flags.

Mark all obvious cases as MPSAFE.  All entries that haven't been marked
as MPSAFE before are by default marked as NEEDGIANT

Approved by:	kib (mentor, blanket)
Commented by:	kib, gallatin, melifaro
Differential Revision:	https://reviews.freebsd.org/D23718
2020-02-26 14:26:36 +00:00
Justin Hibbits
490ebb8f35 powerpc: Fix the NUMA domain list on powernv
Summary:
Consolidate the NUMA associativity handling into a platform function.
Non-NUMA platforms will just fall back to the default (0).  Currently
only implemented for powernv, which uses a lookup table to map the
device tree associativity into a system NUMA domain.

Fixes hangs on powernv after r356534, and corrects a fairly longstanding
bug in powernv's NUMA handling, which ended up using domains 1 and 2 for
devices and memory on power9, while CPUs were bound to domains 0 and 1.

Reviewed by:	bdragon, luporl
Differential Revision:	https://reviews.freebsd.org/D23220
2020-01-18 01:26:54 +00:00
Brandon Bergren
12fe21a3d8 [PowerPC] Ignore fortify-source warning in trap vector copy
Due to a bug in clang 9.0.0 source tracking, the trap vector copying will
always trigger a fortify-source warning.

The destination buffers are 0x2f00 bytes, and the bcopy region is 0x2e00
bytes, so there is not an overflow here.

(I have been running with this patch since September.)
2019-12-27 19:58:14 +00:00
Kyle Evans
db41cd0e06 Kill off dummy kbd drivers
As far as I can tell, these are an artifact of times when linker sets
couldn't be empty, otherwise the kernel build would fail due to unresolved
symbols. hselasky fixed this in r268138, and I've audited the kbd portions
to make sure nothing would blow up due to the empty linker set and
successfully compiled+ran a kernel with no keyboard support at all.

Kill them off now since they're no longer required.

MFC after:	1 week
2019-12-20 16:22:14 +00:00
Leandro Lupori
35f294270c Enable use of ofwcons for early debug
This change enables the use of OpenFirmware Console (ofwcons), even when VGA is
available, allowing early kernel messages to be seen, that is important in case
of crashes before VGA console initialization.

This is specially useful in virtualized environments, where the user/developer
doesn't have full control of the virtualization engine (e.g. OpenStack).

The old behavior is preserved by default and, in order to use ofwcons, a few
tunables that have been introduced need to be set:
- hw.ofwfb.disable=1     - disable OFW FrameBuffer device
- machdep.ofw.mtx_spin=1 - change PPC OFW mutex to SPIN type, to match kernel
                           console's mutex type
- debug.quiesce_ofw=0    - don't call OFW quiesce, needed to keep ofwcons I/O
                           working

More details can be found at differential revision D20640.

Reviewed by:	jhibbits
Differential Revision:	https://reviews.freebsd.org/D20640
2019-12-09 13:40:23 +00:00
Justin Hibbits
9e2b2d6996 powerpc/mpc85xx: Add MSI support for Freescale PowerPC SoCs
Freescale SoCs use a set of IRQs at the high end of the OpenPIC IRQ
list, not counted in the NIRQs of the Feature reporting register.  Some
SoCs include a MSI inbound window in the PCIe controller configuration
registers as well, but some don't.  Currently, this only handles the
SoCs *with* the MSI window.

There are 256 MSIs per MSI bank (32 per MSI IRQ, 8 IRQs per MSI bank).
The P5020 has 3 banks, yielding up to 768 MSIs; older SoCs have only one
bank.
2019-11-08 03:36:19 +00:00
Leandro Lupori
f2c7768cce [PPC] Avoid underflows in NUMA domains
On POWER8 systems with only one memory domain, the "ibm,associativity"
number that corresponds to it is 0, unlike POWER9 systems with two
or more domains, in which the minimum value is 1.

In POWER8 case, subtracting 1 causes an underflow on the unsigned domain
variable and a subsequent index out-of-bounds access.

Reviewed by:	jhibbits
Tested by:	bdragon, luporl
2019-10-22 18:28:58 +00:00
Justin Hibbits
2b50838563 powerpc: Get 32-bit AIM building with secure-PLT
The last few changes needed before 32-bit AIM builds with secure-PLT with
base GCC.  Because ofwcall32.S and swtch32.S were branching to the GOT it
could not use secure PLT.
2019-08-05 01:37:18 +00:00
Nathan Whitehorn
4d210a60c3 Fix bug on newbus device deletion: we should delete the child's devinfo
on deletion, not the parent's.

MFC after:	3 weeks
2019-06-16 21:56:45 +00:00
Leandro Lupori
5d8c3a0657 [PPC64] Fix ofw_initrd
Before this change, OFW initrd (as md) handling code was simulating an ofwbus
device. But as there isn't really a Device Tree (DT) node representing OFW
initrd (it is specified in 2 properties under /chosen), its driver was in fact
stealing other driver's DT node.  This was noticed after MD_ROOT_MEM became
default and QEMU's USB keyboard stopped working under VNC.

This change consists in simplifying the process of detection and mapping of
initrd memory, turning it into a simple startup step, instead of trying to
simulate a device.

Reviewed by:	jhibbits
Differential Revision:	https://reviews.freebsd.org/D20553
2019-06-11 11:16:41 +00:00
Conrad Meyer
e2e050c8ef Extract eventfilter declarations to sys/_eventfilter.h
This allows replacing "sys/eventfilter.h" includes with "sys/_eventfilter.h"
in other header files (e.g., sys/{bus,conf,cpu}.h) and reduces header
pollution substantially.

EVENTHANDLER_DECLARE and EVENTHANDLER_LIST_DECLAREs were moved out of .c
files into appropriate headers (e.g., sys/proc.h, powernv/opal.h).

As a side effect of reduced header pollution, many .c files and headers no
longer contain needed definitions.  The remainder of the patch addresses
adding appropriate includes to fix those files.

LOCK_DEBUG and LOCK_FILE_LINE_ARG are moved to sys/_lock.h, as required by
sys/mutex.h since r326106 (but silently protected by header pollution prior
to this change).

No functional change (intended).  Of course, any out of tree modules that
relied on header pollution for sys/eventhandler.h, sys/lock.h, or
sys/mutex.h inclusion need to be fixed.  __FreeBSD_version has been bumped.
2019-05-20 00:38:23 +00:00
Justin Hibbits
7d91f528a6 powerpc: hide innocuous printf behind bootverbose
NUMA associativity, and OFW node existence, is completely optional, and
shouldn't warn always.
2019-05-08 03:15:22 +00:00
Justin Hibbits
49d9a59783 Add NUMA support to powerpc
Summary:
Initial NUMA support:
    - associate CPU with domain
    - associate memory ranges with domain
    - identify domain for devices
    - limit device interrupt binding to appropriate domain

- Additionally fixes a bug in the setting of Maxmem which led to
  only memory attached to the first socket being enabled for DMA

A pmap variant can opt in to numa support by by calling `numa_mem_regions`
at the end of pmap_bootstrap - registering the corresponding ranges with the
VM.

This yields a ~20% improvement in build times of llvm on dual socket POWER9
over non-NUMA.

Original patch by mmacy.

Differential Revision: https://reviews.freebsd.org/D17933
2019-04-13 04:03:18 +00:00
Justin Hibbits
0499e9c619 powerpc64: Use medium code model in asm files for TOC references
Summary:
With a sufficiently large TOC, it's possible to index out of range, as
the immediate load instructions only permit 16-bit indices, allowing up
to 64kB range (signed) from the base pointer.  Allow +/- 2GB range, with
the medium code model TOC accesses in asm.

Patch originally by Brandon Bergren.  The issue appears to impact ELFv2
more than ELFv1.

Reviewed by:	luporl
Differential Revision: https://reviews.freebsd.org/D19708
2019-03-29 02:38:30 +00:00
Justin Hibbits
4290b4b849 powerpc: Bind IRQs to only one interrupt on QorIQ SoCs
The QorIQ SoCs don't actually support multicast interrupts, and the
references state explicitly that multicast is undefined behavior.  Avoid the
undefined behavior by binding to only a single CPU, using a quirk to
determine if this is necessary.

MFC after:	3 weeks
2019-02-06 03:52:14 +00:00
Justin Hibbits
bfed756af6 Sprinkle EARLY_DRIVER_MODULE around the tree
Mark some buses as BUS_PASS_BUS, and some resources as BUS_PASS_RESOURCE.
This also decouples some resource attachment orderings from being races by
device tree ordering, instead relying on the bus pass to provide the
ordering.

This was originally intended to support multipass suspend/resume, but it's
also needed on PowerMacs when using fdt, as the device tree seems to get
created in reverse of the OFW tree.
Reviewed by:	nwhitehorn (long ago)
Differential Revision:	https://reviews.freebsd.org/D918
2018-12-04 04:55:49 +00:00
Justin Hibbits
fd8cf3be5f powerpc: Blacklist the top 64kB range of the lower 4GB PA space
The PHB4 host bridge used by the POWER9 uses a 64kB range in 32-bit
space at the address 0xffff0000-0xffffffff.  Reserve this range so that
DMA memory cannot be allocated within this range.  This fixes seemingly
random crashes on a POWER9 system.  Ideally this range will have been
reserved by the firmware, but as of now this is not the case.

Submitted by:	git_bdragon.rtk0.net
Reviewed by:	nwhitehorn
Approved by:	re(kib)
Differential Revision:	https://reviews.freebsd.org/D17183
2018-09-25 02:34:28 +00:00
Breno Leitao
3ddc2cde51 ofw: Load initrd file
This is an OFW initrd module that would load the initrd from device tree
parameters and give the to the md driver.

With this patch, it is possible to pass a rootfs image through kexec in PowerNV
mode (powerpc64). In order to user it, you should set the MD_ROOT_MEM option in
your kernel configuration.

Reviewed by: jhibbits
Approved by: jhibbits (mentor)
Differential Revision: https://reviews.freebsd.org/D15705
2018-07-24 16:52:52 +00:00
Breno Leitao
6d645c57a3 Fix excise_initrd_region() to support 32- and 64-bit initrd params.
Changed excise_initrd_region to support both 32- and 64-bit
values for linux,initrd-start and linux,initrd-end.

This fixes the boot problem on some machines after rS334485.

Submitted by: Luis Pires <lffpires@ruabrasil.org>
Reviewed by: jhibbits, leitao
Approved by: jhibbits (mentor)
Differential Revision: https://reviews.freebsd.org/D15667
2018-06-07 21:24:21 +00:00
Breno Leitao
48f64992f2 powerpc64: Avoid overwriting initrd area
Currently kexec loads an initrd file into the main memory but does not
mark that region as reserved, thus the area is not protected.

If any initrd/md file is loaded from kexec/petitboot, the region might become
corarupted/overwritten since FreeBSD does not know the region is 'reserved'.

This patch simply adds the initrd area as a reserved memory region.

Approved by: jhibbits
Differential Revision: https://reviews.freebsd.org/D15610
2018-06-01 12:43:13 +00:00
Justin Hibbits
c07c77a311 Fix a manual copy from the original diff for r333825
The 'else' was in the original diff.

Submitted by:	Breno Leitao
2018-05-19 03:47:28 +00:00
Justin Hibbits
876f3b9295 Add yet another option for gathering available memory
On some POWER9 systems, 'reg' denotes the full memory in the system, while
'linux,usable-memory' denotes the usable memory.  Some memory is reserved for
NVLink usage, so is partitioned off.

Submitted by:	Breno Leitao
2018-05-19 03:45:38 +00:00
Justin Hibbits
42ca1d5cc3 Increase the fdtmemreserv array limit to boot on POWER9
Discussing with others, this needs to be at least 20 to boot on some POWER9
nodes.  Linux made a similar change for the same reason, so increase to 32
to give us some extra breathing room as well.  The input and output arrays
are sized at 256, so much greater than the increase in the property array
size.
2018-04-25 02:42:11 +00:00
Justin Hibbits
d6d0670814 powerpc/ofw: Fix malloc inside lock
Summary:
Currently ofw_real_bounce_alloc() is requesting memory, using WAITOK, holding a
non-sleepable locks, called 'OF Bounce Page'.

Fix this by allocating the pages outside of the lock, and only updating the
global variables while holding the lock.

Submitted by:	Breno Leitao
Differential Revision:	https://reviews.freebsd.org/D14955
2018-04-08 16:43:56 +00:00
Nathan Whitehorn
8864f35942 Execute PowerPC64/AIM kernel from direct map region when possible.
When the kernel can be in real mode in early boot, we can execute from
high addresses aliased to the kernel's physical memory. If that high
address has the first two bits set to 1 (0xc...), those addresses will
automatically become part of the direct map. This reduces page table
pressure from the kernel and it sets up the kernel to be used with
radix translation, for which it has to be up here.

This is accomplished by exploiting the fact that all PowerPC kernels are
built as position-independent executables and relocate themselves
on start. Before this patch, the kernel runs at 1:1 VA:PA, but that
VA/PA is random and set by the bootloader. Very early, it processes
its ELF relocations to operate wherever it happens to find itself.
This patch uses that mechanism to re-enter and re-relocate the kernel
a second time witha new base address set up in the early parts of
powerpc_init().

Reviewed by:	jhibbits
Differential Revision:	D14647
2018-03-13 15:03:58 +00:00
Nathan Whitehorn
35feca377d Make FDT-using parts of ofw_machdep.c condition on options FDT. This fixes
the kernel build when options FDT is absent.
2018-03-11 01:09:31 +00:00
Nathan Whitehorn
f9edb09d70 Move the powerpc64 direct map base address from zero to high memory. This
accomplishes a few things:
- Makes NULL an invalid address in the kernel, which is useful for catching
  bugs.
- Lays groundwork for radix-tree translation on POWER9, which requires the
  direct map be at high memory.
- Similarly lays groundwork for a direct map on 64-bit Book-E.

The new base address is chosen as the base of the fourth radix quadrant
(the minimum kernel address in this translation mode) and because all
supported CPUs ignore at least the first two bits of addresses in real
mode, allowing direct-map addresses to be used in real-mode handlers.
This is required by Linux and is part of the architecture standard
starting in POWER ISA 3, so can be relied upon.

Reviewed by:	jhibbits, Breno Leitao
Differential Revision:	D14499
2018-03-07 17:08:07 +00:00
Nathan Whitehorn
65184f89b6 Set internal error returns for OF_peer(), OF_child(), and OF_parent() to
zero, matching the IEEE 1275 standard. Since these internal error paths
have never, to my knowledge, been taken, behavior is unchanged.

Reported by:	gonzo
MFC after:	2 weeks
2018-02-19 15:49:14 +00:00
Nathan Whitehorn
222393d5ca Chase removal of FDT fixup code on PowerPC in r327907. 2018-01-13 03:09:05 +00:00
Nathan Whitehorn
2ad331874e Remove ELF note for Open Firmware. It is marked optional in a single 1996
draft of a never-finalized standard (CHRP) and is irrelevant in practice
on FreeBSD since we load the kernel with loader(8) on Open Firmware
platforms anyway. Moreover, loader(8), which is directly loaded by Open
Firmware, has never had an equivalent note.

MFC after:	2 weeks
2017-12-28 23:49:53 +00:00
Nathan Whitehorn
2bfca5775b Back out OF module installation in the event of failure. PS3 firmware gives
some ancient FDT version (2) that fails the init check in OFW_FDT. It is
still possible to make progress, but not while the OF layer is going crazy.
2017-11-28 06:31:39 +00:00
Pedro F. Giffuni
71e3c3083b sys/powerpc: further adoption of SPDX licensing ID tags.
Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.
2017-11-27 15:09:59 +00:00
Nathan Whitehorn
91419bdafd Avoid assumptions about the BSP being CPU 0.
MFC after:	3 weeks
2017-11-25 23:23:24 +00:00
Nathan Whitehorn
c0650b2f69 When booting from an FDT, make sure the FDT itself isn't included the range
of available memory. Boot loaders are supposed to add a reserved entry for
it, but not all do.

MFC after:	2 weeks
2017-11-25 22:14:30 +00:00
Justin Hibbits
bb7137e1a3 Stop special casing 32-bit AIM in memory parsing
There's no need to special case 32-bit AIM to short circuit processing.
Some AIM CPUs can handle 36 bit addresses, and 64-bit CPUs can run 32-bit
OSes, so this will allow us to expand for that in the future if we desire.
2017-11-17 04:10:52 +00:00
Justin Hibbits
95ce4c00ec No need to check for AIM here
This block is already in a #ifdef AIM block.
2017-10-20 03:13:31 +00:00
Patrick Kelsey
67d955aab4 Corrected misspelled versions of rendezvous.
The MFC will include a compat definition of smp_no_rendevous_barrier()
that calls smp_no_rendezvous_barrier().

Reviewed by:	gnn, kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D10313
2017-04-09 02:00:03 +00:00
Justin Hibbits
62c6b30e5c Fix booting with >4GB RAM on PowerMac G5 hardware
===
From Nathan Whitehorn:

Open Firmware runs in virtual mode on the Powermac G5. This runs inside the
kernel page table, which preserves all address translations made by OF before
the kernel starts; as a result, the kernel address space is a strict superset of
OF's.

Where this explodes is if OF uses an unmapped SLB entry. The SLB fault handler
runs in real mode and refers to the PCPU pointer in SPRG0, which blows up the
kernel. Having a value of SPRG0 that works for the kernel is less fatal than
preserving OF's value in this case.

===

The result of this is seemingly random panics from NULL dereferences, or hangs
immediately upon boot.  By not restoring SPRG0 for Open Firmware entry the
kernel PCPU pointer is preserved and SLB faults are successful, resulting in a
stable kernel.

PR:		205458
Reported by:	several (over bugzilla, lists, IRC)
Reviewed by:	andreast
Tested by:	many (various forms)
MFC after:	2 weeks
2017-03-07 22:11:57 +00:00