The CPU_FTR_POWER9_DD2_1 flag is intended to be set for DD2.1 and
above (which is what the dt_cpu_ftrs setup does). Fix cputable for
DD2.2 to match.

This came about due to patches b5af4f27 ("powerpc: Add CPU feature
bits for TM bug workarounds on POWER9 v2.2"), and 9e9626ed
("powerpc/64s: Fix POWER9 DD2.2 and above in DT CPU features") being
in-flight at once. The latter patch fixed dt_cpu_ftrs like this one
does. The former changed cputable to match dt_cpu_ftrs.

Fixes: b5af4f27 ("powerpc: Add CPU feature bits for TM bug workarounds on POWER9 v2.2")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

The pkey code added a CPU_FTR_PKEY bit, but did not add it to the
dt_cpu_ftrs feature set. Although capability is supported by all
processors in the base dt_cpu_ftrs set for 64s, it's a significant
and sufficiently well defined feature to make it optional. So add
it as a quirk for now, which can be versioned out then controlled
by the firmware (once dt_cpu_ftrs gains versioning support).

Fixes: cf43d3b2 ("powerpc: Enable pkey subsystem")
Cc: stable@vger.kernel.org # v4.16+
Cc: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Presently the dt_cpu_ftrs restore_cpu will only add bits to the LPCR
for secondaries, but some bits must be removed (e.g., UPRT for HPT).
Not clearing these bits on secondaries causes checkstops when booting
with disable_radix.

restore_cpu can not just set LPCR, because it is also called by the
idle wakeup code which relies on opal_slw_set_reg to restore the value
of LPCR, at least on P8 which does not save LPCR to stack in the idle
code.

Fix this by including a mask of bits to clear from LPCR as well, which
is used by restore_cpu.

This is a little messy now, but it's a minimal fix that can be
backported.  Longer term, the idle SPR save/restore code can be
reworked to completely avoid calls to restore_cpu, then restore_cpu
would be able to unconditionally set LPCR to match boot processor
environment.

Fixes: 5a61ef74 ("powerpc/64s: Support new device tree binding for discovering CPU features")
Cc: stable@vger.kernel.org # v4.12+
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

As described in that commit:

  When stop is executed with EC=ESL=0, it appears to execute like a
  normal instruction (resuming from NIP when woken by interrupt). So
  all the save/restore handling can be avoided completely.

This is true, except in the case of an NMI interrupt (sreset or
machine check) interrupting the instruction. In that case, the NMI
gets an "interrupt occurred while the processor was in power-saving
mode" indication. The power-save wakeup code uses that bit to decide
whether to restore some registers (e.g., LR). Because these are no
longer saved, this causes random register corruption.

It may be possible to restore this optimisation by detecting the case
of no register loss on the wakeup side, and avoid restoring in that
case, but that's not a minor fix because the wakeup code itself uses
some registers that would be live (e.g., LR).

Fixes: b9ee31e1 ("powerpc/64s/idle: POWER9 ESL=0 stop avoid save/restore overhead")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

These functions will be introduced into the generic iomap.c so they
can deal with PIO accesses in hi-lo/lo-hi variants. Thus, the powerpc
version of iomap.c will need to provide the same functions even
though, in this arch, they are identical to the regular
io{read|write}64 functions.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Tested-by: Horia Geantă <horia.geanta@nxp.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Subsequent patches in this series makes use of the readq and writeq
defines in iomap.h. However, as is, they get missed on the powerpc
platform seeing the include comes before the define. This patch moves
the include down to fix this.
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

cxllib_handle_fault() is called by an external driver when it needs to
have the host resolve page faults for a buffer. The buffer can cover
several pages and VMAs. The function iterates over all the pages used
by the buffer, based on the page size of the VMA.

To ensure some stability while processing the faults, the thread T1
grabs the mm->mmap_sem semaphore with read access (R1). However, when
processing a page fault for a single page, one of the underlying
functions, copro_handle_mm_fault(), also grabs the same semaphore with
read access (R2). So the thread T1 takes the semaphore twice.

If another thread T2 tries to access the semaphore in write mode W1
(say, because it wants to allocate memory and calls 'brk'), then that
thread T2 will have to wait because there's a reader (R1). If the
thread T1 is processing a new page at that time, it won't get an
automatic grant at R2, because there's now a writer thread
waiting (T2). And we have a deadlock.

The timeline is:
1. thread T1 owns the semaphore with read access R1
2. thread T2 requests write access W1 and waits
3. thread T1 requests read access R2 and waits

The fix is for the thread T1 to release the semaphore R1 once it got
the information it needs from the current VMA. The address space/VMAs
could evolve while T1 iterates over the full buffer, but in the
unlikely case where T1 misses a page, the external driver will raise a
new page fault when retrying the memory access.

Fixes: 3ced8d73 ("cxl: Export library to support IBM XSL")
Cc: stable@vger.kernel.org # 4.13+
Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

We get the below warning if we try to use kexec on P9:
   kexec_core: Starting new kernel
   WARNING: CPU: 0 PID: 1223 at arch/powerpc/kernel/process.c:826 __set_breakpoint+0xb4/0x140
   [snip]
   NIP __set_breakpoint+0xb4/0x140
   LR  kexec_prepare_cpus_wait+0x58/0x150
   Call Trace:
     0xc0000000ee70fb20 (unreliable)
     0xc0000000ee70fb20
     default_machine_kexec+0x234/0x2c0
     machine_kexec+0x84/0x90
     kernel_kexec+0xd8/0xe0
     SyS_reboot+0x214/0x2c0
     system_call+0x58/0x6c

This happens since we are trying to clear hw breakpoint on POWER9,
though we don't have CPU_FTR_DAWR enabled. Guard __set_breakpoint()
within hw_breakpoint_disable() with ppc_breakpoint_available() to
address this.

Fixes: 96541531 ("powerpc: Disable DAWR in the base POWER9 CPU features")
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

kernel parameter disable_radix takes different options
disable_radix=yes|no|1|0  or just disable_radix.

prom_init parsing is not supporting these options.

Fixes: 1fd6c022 ("powerpc/mm: Add a CONFIG option to choose if radix is used by default")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

kernel parameter disable_radix takes different options
disable_radix=yes|no|1|0 or just disable_radix. When using the later
format we get below error.

 `Malformed early option 'disable_radix'`

Fixes: 1fd6c022 ("powerpc/mm: Add a CONFIG option to choose if radix is used by default")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

With 64k page size, we have hugetlb pte entries at the pmd and pud level for
book3s64. We don't need to create a separate page table cache for that. With 4k
we need to make sure hugepd page table cache for 16M is placed at PUD level
and 16G at the PGD level.

Simplify all these by not using HUGEPD_PD_SHIFT which is confusing for book3s64.

Without this patch, with 64k page size we create pagetable caches with shift
value 10 and 7 which are not used at all.

Fixes: 419df06e ("powerpc: Reduce the PTE_INDEX_SIZE")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

With split PTL (page table lock) config, we allocate the level
4 (leaf) page table using pte fragment framework instead of slab cache
like other levels. This was done to enable us to have split page table
lock at the level 4 of the page table. We use page->plt backing the
all the level 4 pte fragment for the lock.

Currently with Radix, we use only 16 fragments out of the allocated
page. In radix each fragment is 256 bytes which means we use only 4k
out of the allocated 64K page wasting 60k of the allocated memory.
This was done earlier to keep it closer to hash.

This patch update the pte fragment count to 256, thereby using the
full 64K page and reducing the memory usage. Performance tests shows
really low impact even with THP disabled. With THP disabled we will be
contenting further less on level 4 ptl and hence the impact should be
further low.

  256 threads:
    without patch (10 runs of ./ebizzy  -m -n 1000 -s 131072 -S 100)
      median = 15678.5
      stdev = 42.1209

    with patch:
      median = 15354
      stdev = 194.743

This is with THP disabled. With THP enabled the impact of the patch
will be less.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Adds more code comments. We also remove an unnecessary pkey check
after we check for pkey error in this patch.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

When stop is executed with EC=ESL=0, it appears to execute like a
normal instruction (resuming from NIP when woken by interrupt). So all
the save/restore handling can be avoided completely. In particular NV
GPRs do not have to be saved, and MSR does not have to be switched
back to kernel MSR.

So move the test for EC=ESL=0 sleep states out to power9_idle_stop,
and return directly to the caller after stop in that case.

This improves performance for ping-pong benchmark with the stop0_lite
idle state by 2.54% for 2 threads in the same core, and 2.57% for
different cores. Performance increase with HV_POSSIBLE defined will be
improved further by avoiding the hwsync.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Commit 3d4fbffd ("powerpc/64s/idle: POWER9 implement a separate
idle stop function for hotplug") that added power9_offline_stop() was
written before commit 7672691a ("powerpc/powernv: Provide a way to
force a core into SMT4 mode").

When merging the former I failed to notice that it caused us to skip
the force-SMT4 logic for offline CPUs. The result is that offlined
CPUs will not correctly participate in the force-SMT4 logic, which
presumably will result in badness (not tested).

Reconcile the two commits by making power9_offline_stop() a pre-cursor
to power9_idle_stop(), so that they share the force-SMT4 logic.

This is based on an original commit from Nick, all breakage is my own.

Fixes: 3d4fbffd ("powerpc/64s/idle: POWER9 implement a separate idle stop function for hotplug")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Currently powernv reboot and shutdown requests just leave secondaries
to do their own things. This is undesirable because they can trigger
any number of watchdogs while waiting for reboot, but also we don't
know what else they might be doing -- they might be causing trouble,
trampling memory, etc.

The opal scheduled flash update code already ran into watchdog problems
due to flashing taking a long time, and it was fixed with 2196c6f1
("powerpc/powernv: Return secondary CPUs to firmware before FW update"),
which returns secondaries to opal. It's been found that regular reboots
can take over 10 seconds, which can result in the hard lockup watchdog
firing,

  reboot: Restarting system
  [  360.038896709,5] OPAL: Reboot request...
  Watchdog CPU:0 Hard LOCKUP
  Watchdog CPU:44 detected Hard LOCKUP other CPUS:16
  Watchdog CPU:16 Hard LOCKUP
  watchdog: BUG: soft lockup - CPU#16 stuck for 3s! [swapper/16:0]

This patch removes the special case for flash update, and calls
smp_send_stop in all cases before calling reboot/shutdown.

smp_send_stop could return CPUs to OPAL, the main reason not to is
that the request could come from a NMI that interrupts OPAL code,
so re-entry to OPAL can cause a number of problems. Putting
secondaries into simple spin loops improves the chances of a
successful reboot.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

The hard lockup watchdog can fire under local_irq_disable
on platforms with irq soft masking.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Use the NMI IPI rather than smp_call_function for smp_send_stop.
Have stopped CPUs hard disable interrupts rather than just soft
disable.

This function is used in crash/panic/shutdown paths to bring other
CPUs down as quickly and reliably as possible, and minimizing their
potential to cause trouble.

Avoiding the Linux smp_call_function infrastructure and (if supported)
using true NMI IPIs makes this more robust.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

The PSSCR value is not stored to PACA_REQ_PSSCR if the CPU does not
have the XER[SO] bug.

Fix this by storing up-front, outside the workaround code. The initial
test is not required because it is a slow path.

The workaround is made to depend on CONFIG_KVM_BOOK3S_HV_POSSIBLE, to
match pnv_power9_force_smt4_catch() where it is used. Drop the comment
on pnv_power9_force_smt4_catch() as it's no longer true.

Fixes: 7672691a ("powerpc/powernv: Provide a way to force a core into SMT4 mode")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

The recent commit 15a3204d ("powerpc/64s: Set assembler machine
type to POWER4") set the machine type in our ASFLAGS when building the
kernel, and removed some ".machine power4" directives from various asm
files.

This broke the selftests build on old toolchains (that don't assume
Power4), because we build the kernel source files into the selftests
using different ASFLAGS.

The fix is simply to add -mpower4 to the selftest ASFLAGS as well.

Fixes: 15a3204d ("powerpc/64s: Set assembler machine type to POWER4")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

After migration the security feature flags might have changed (e.g.,
destination system with unpatched firmware), but some flags are not
set/clear again in init_cpu_char_feature_flags() because it assumes
the security flags to be the defaults.

Additionally, if the H_GET_CPU_CHARACTERISTICS hypercall fails then
init_cpu_char_feature_flags() does not run again, which potentially
might leave the system in an insecure or sub-optimal configuration.

So, just restore the security feature flags to the defaults assumed
by init_cpu_char_feature_flags() so it can set/clear them correctly,
and to ensure safe settings are in place in case the hypercall fail.

Fixes: f636c147 ("powerpc/pseries: Set or clear security feature flags")
Depends-on: 19887d6a28e2 ("powerpc: Move default security feature flags")
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

This moves the definition of the default security feature flags
(i.e., enabled by default) closer to the security feature flags.

This can be used to restore current flags to the default flags.
Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

flush_thread() calls __set_breakpoint() via set_debug_reg_defaults()
without checking ppc_breakpoint_available(). On Power8 or later CPUs
which have the DAWR feature disabled that will cause a write to the
DABR which is incorrect as those CPUs don't have a DABR.

Fix it two ways, by checking ppc_breakpoint_available() in
set_debug_reg_defaults(), and also by reworking __set_breakpoint() to
only write to DABR on Power7 or earlier.

Fixes: 96541531 ("powerpc: Disable DAWR in the base POWER9 CPU features")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Rework the logic in __set_breakpoint()]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kvm/book3s_hv.c: In function ‘kvmppc_h_set_mode’:
arch/powerpc/kvm/book3s_hv.c:745:8: error: implicit declaration of function ‘ppc_breakpoint_available’
   if (!ppc_breakpoint_available())
        ^~~~~~~~~~~~~~~~~~~~~~~~

Fixes: 398e712c ("KVM: PPC: Book3S HV: Return error from h_set_mode(SET_DAWR) on POWER9")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Commit 8e0b634b ("powerpc/64s: Do not allocate lppaca if we are
not virtualized") removed allocation of lppaca on bare metal
platforms. But with CONFIG_PPC_SPLPAR enabled, we still access the
lppaca on bare metal in some code paths.

Fix this but adding runtime checks for SPLPAR (shared processor LPAR).

Fixes: 8e0b634b ("powerpc/64s: Do not allocate lppaca if we are not virtualized")
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

In commit 9690c157 ("powerpc/mm/radix: Fix always false comparison
against MMU_NO_CONTEXT") an issue was discovered where `mm->context.id` was
being truncated to an `unsigned int`, while the PID is actually an
`unsigned long`. Update the earlier patch by fixing one remaining
occurrence. Discovered during a compilation with W=1:

  arch/powerpc/mm/tlb-radix.c:702:19: error: comparison is always false due to limited range of data type [-Werror=type-limits]
Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

When using SIG_DBG_BRANCH_TRACING, MSR.BE is left enabled in the
user context when single_step_exception() prepares the SIGTRAP
delivery.  The resulting branch-trap-within-the-SIGTRAP-handler
isn't healthy.

Commit 2538c2d0 broke this, by
replacing an MSR mask operation of ~(MSR_SE | MSR_BE) with a call
to clear_single_step() which only clears MSR_SE.

This patch adds a new helper, clear_br_trace(), which clears the
debug trap before invoking the signal handler.  This helper is a
NOP for BookE as SIG_DBG_BRANCH_TRACING isn't supported on BookE.
Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

This reduces vmlinux text size by 1kB and data by 1.5kB with a small
build!
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Add the recently added CPU_FTRS_POWER9_DD2_2 to the little
      endian possible mask as noticed by Nick.]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Add GENERIC_CPU support for little-endian rather than using POWER8
specific selection for POWER9 and above.

Restrict GENERIC_CPU to POWER8 and above on little endian.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Duplicate GENERIC_CPU to avoid a kbuild warning about the prompt
      being redefined. Spell out that GENERIC means >= POWER4 for BE.]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

POWER4 has been broken since at least the change 49d09bf2
("powerpc/64s: Optimise MSR handling in exception handling"), which
requires mtmsrd L=1 support. This was introduced in ISA v2.01, and
POWER4 supports ISA v2.00.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

The last usage was removed in c17b98cf ("KVM: PPC: Book3S HV:
Remove code for PPC970 processors") (Dec 2014).
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

The CPU_FTR_POWER9_DD2_1 flag is intended to be set for DD2.1 and
above (which is what the cputable setup does). Fix DT CPU features
quirk setup to match.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Merge with upstream changes]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Rather than override the machine type in .S code (which can hide wrong
or ambiguous code generation for the target), set the type to power4
for all assembly.

This also means we need to be careful not to build power4-only code
when we're not building for Book3S, such as the "power7" versions of
copyuser/page/memcpy.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Fix Book3E build, don't build the "power7" variants for non-Book3S]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

ALTIVEC and VSX features are not added by to default to the POWERx CPU
feature sets because they are intended to be enabled by firmware.
Currently they end up in CPU_FTRS_POSSIBLE due to their inclusion in
other the set for other CPUs, eg. PPC970.

But they should be added individually to the CPU_FTRS_POSSIBLE set,
because if we reduce the set of CPUs that are built-for they may
disappear from the possible mask.

It already contains CPU_FTR_VSX, so add ALTIVEC. The _COMP features
should be used because they won't be present if compiled out.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Add detail to change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

It's not a bug to have features missing in CPU_FTR_ALWAYS, but it is a
missed opportunity for optimisation.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

When building a uImage or zImage using ppc6xx_defconfig and some other
defconfigs, the following error occurs with GCC 4.5.1:

  /arch/powerpc/boot/libfdt_env.h:10:13: error: redefinition of typedef 'uint32_t'
  /arch/powerpc/boot/types.h:21:13: note: previous declaration of 'uint32_t' was here
  /arch/powerpc/boot/libfdt_env.h:11:13: error: redefinition of typedef 'uint64_t'
  /arch/powerpc/boot/types.h:22:13: note: previous declaration of 'uint64_t' was here

The problem is that commit 656ad58e (powerpc/boot: Add OPAL
console to epapr wrappers) adds typedefs for uint32_t and uint64_t to
type.h but doesn't remove the pre-existing (and now duplicate)
typedefs from libfdt_env.h.

Fix the error by removing the duplicate typedefs from libfdt_env.h
Signed-off-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

When waking from a CPU idle instruction (e.g., nap or stop), the sync
for ordering the KVM secondary thread state can be avoided if there
wakeup is coming from a kernel context rather than KVM context.

This improves performance for ping-pong benchmark with the stop0 idle
state by 0.46% for 2 threads in the same core, and 1.02% for different
cores.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Implement a new function to invoke stop, power9_offline_stop, which is
like power9_idle_stop but used by the cpu hotplug code.

Move KVM secondary state manipulation code to the offline case.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

system_reset_exception does most of its own crash handling now,
invoking the debugger or crash dumps if they are registered. If not,
then it goes through to die() to print stack traces, and then is
supposed to panic (according to comments).

However after die() prints oopses, it does its own handling which
doesn't allow system_reset_exception to panic (e.g., it may just
kill the current process). This patch causes sreset exceptions to
return from die after it prints messages but before acting.

This also stops die from invoking the debugger on 0x100 crashes.
system_reset_exception similarly calls the debugger. It had been
thought this was harmless (because if the debugger was disabled,
neither call would fire, and if it was enabled the first call
would return). However in some cases like xmon 'X' command, the
debugger returns 0, which currently causes it to be entered
again (first in system_reset_exception, then in die), which is
confusing.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>