Commit 59a53afe "powerpc: Don't setup
CPUs with bad status" broke ePAPR SMP booting.  ePAPR says that CPUs
that aren't presently running shall have status of disabled, with
enable-method being used to determine whether the CPU can be enabled.

Fix by checking for spin-table, which is currently the only supported
enable-method.
Signed-off-by: NScott Wood <scottwood@freescale.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Emil Medve <Emilian.Medve@Freescale.com>
Cc: stable@vger.kernel.org
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The commit 71ec7c55 introduced the magic symbol ".TOC." for ELFv2 ABI.
This symbol is built manually and has no CRC value computed. A zero value
is put in the CRC section to avoid modpost complaining about a missing CRC.
Unfortunately, this breaks the kernel module loading when the kernel is
relocated (kdump case for instance) because of the relocation applied to
the kcrctab values.

This patch compute a CRC value for the TOC symbol which will match the one
compute by the kernel when it is relocated - aka '0 - relocate_start' done in
maybe_relocated called by check_version (module.c).
Signed-off-by: NLaurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Anton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

In commit 27f44888 "Add OPAL takeover from PowerVM" we added support
for "takeover" on OPAL v1 machines.

This was a mode of operation where we would boot under pHyp, and query
for the presence of OPAL. If detected we would then do a special
sequence to take over the machine, and the kernel would end up running
in hypervisor mode.

OPAL v1 was never a supported product, and was never shipped outside
IBM. As far as we know no one is still using it.

Newer versions of OPAL do not use the takeover mechanism. Although the
query for OPAL should be harmless on machines with newer OPAL, we have
seen a machine where it causes a crash in Open Firmware.

The code in early_init_devtree() to copy boot_command_line into cmd_line
was added in commit 817c21ad "Get kernel command line accross OPAL
takeover", and AFAIK is only used by takeover, so should also be
removed.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The DART table allocation is registered to kmemleak via the
memblock_alloc_base() call. However, the DART table is later unmapped
and dart_tablebase VA no longer accessible. This patch tells kmemleak
not to scan this block and avoid an unhandled paging request.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

This variable is of the wrong type, everywhere it is used it
should be an unsigned int rather than a int.
Signed-off-by: NRickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

In commit 721aeaa9 "Build little endian ppc64 kernel with ABIv2", we
missed some updates required in the kprobes code to make jprobes work
when the kernel is built with ABI v2.

Firstly update arch_deref_entry_point() to do the right thing. Now that
we have added ppc_global_function_entry() we can just always use that, it
will do the right thing for 32 & 64 bit and ABI v1 & v2.

Secondly we need to update the code that sets up the register state before
calling the jprobe handler. On ABI v1 we setup r2 to hold the TOC, on ABI
v2 we need to populate r12 with the function entry point address.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The printks() in our ftrace code have no prefix, so they appear on the
console with very little context, eg:

  Branch out of range

Use pr_fmt() & pr_err() to add a prefix. While we're at it, collapse a
few split lines that don't need to be, and add a missing newline to one
message.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

There is a bug in the handling of the function entry when we are nopping
out a branch from a module in ftrace.

We compare the result of module_trampoline_target() with the value of
ppc_function_entry(), and expect them to be true. But they never will
be.

module_trampoline_target() will always return the global entry point of
the function, whereas ppc_function_entry() will always return the local.

Fix it by using the newly added ppc_global_function_entry().
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

In commit 24a1bdc3, "Fix ABIv2 issues with __ftrace_make_call", Anton
changed the logic that creates and patches the branch, and added a
thinko in the check of create_branch(). create_branch() returns the
instruction that was generated, so if we get zero then it succeeded.

The result is we can't ftrace modules:

  Branch out of range
  WARNING: at ../kernel/trace/ftrace.c:1638
  ftrace failed to modify [<d000000004ba001c>] fuse_req_init_context+0x1c/0x90 [fuse]

We should probably fix patch_instruction() to do that check and make the
API saner, but that's a separate patch. For now just invert the test.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

In commit 24a1bdc3, "Fix ABIv2 issues with __ftrace_make_call", Anton
changed the logic that checks for the expected code sequence when
patching a module.

We missed the typo in the mask, 0xffff00000 should be 0xffff0000, which
has the effect of making the test always true.

That makes it impossible to ftrace against modules, eg:

  Unexpected call sequence: 48000008 e8410018
  WARNING: at ../kernel/trace/ftrace.c:1638
  ftrace failed to modify [<d000000007cf001c>] rng_dev_open+0x1c/0x70 [rng_core]
Reported-by: NDavid Binderman <dcb314@hotmail.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

ABIv2 has the concept of a global and local entry point to a function.
In most cases we are interested in the local entry point, and so that is
what ppc_function_entry() returns.

However we have a case in the ftrace code where we want the global entry
point, and there may be other places we need it too. Rather than special
casing each, add an accessor.

For ABIv1 and 32-bit there is only a single entry point, so we return
that. That means it's safe for the caller to use this without also
checking the ABI version.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The generic code uses gcc built-ins which work fine so there's no benefit
in implementing our own anymore.

We can't completely remove the ld/st_le* functions as some historical
cruft still uses them, but that's next on the radar
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

We have some compile-time disabled debug code in signal_xx.c. It's from
some ancient time BG, almost certainly part of the original port, given
the very similar code on other arches.

The show_unhandled_signal logic, added in d0c3d534 (2.6.24) is
cleaner and prints more useful information, so drop the debug code.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

In arch/powerpc/kernel/iomap.c, lots of IO reading accessors missed
to check EEH error as Ben pointed. The patch fixes it.

For the writing accessors, we change the called functions only for
making them look similar to the reading counterparts.
Suggested-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The rule to create the final images uses a zImage.% pattern.
Unfortunately, this also matches the names of the zImage.*.lds linker
scripts, which appear as a dependency of the final images. This somehow
worked when $(srctree) used to be an absolute path, but now the pattern
matches too much. List only the images from $(image-y) as the target of
the rule, to avoid the circular dependency.
Reported-and-tested-by: NMike Qiu <qiudayu@linux.vnet.ibm.com>
Signed-off-by: NMichal Marek <mmarek@suse.cz>

Commit 2749a2f2 (powerpc/book3s: Fix machine check handling for
unhandled errors) introduced a few ABIv2 issues.

We can maintain ABIv1 and ABIv2 compatibility by branching to the
function rather than the dot symbol.

Fixes: 2749a2f2 ("powerpc/book3s: Fix machine check handling for unhandled errors")
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Currently we forward MCEs to guest which have been recovered by guest.
And for unhandled errors we do not deliver the MCE to guest. It looks like
with no support of FWNMI in qemu, guest just panics whenever we deliver the
recovered MCEs to guest. Also, the existig code used to return to host for
unhandled errors which was casuing guest to hang with soft lockups inside
guest and makes it difficult to recover guest instance.

This patch now forwards all fatal MCEs to guest causing guest to crash/panic.
And, for recovered errors we just go back to normal functioning of guest
instead of returning to host. This fixes soft lockup issues in guest.
This patch also fixes an issue where guest MCE events were not logged to
host console.
Signed-off-by: NMahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

We don't see MCE counter getting increased in /proc/interrupts which gives
false impression of no MCE occurred even when there were MCE events.
The machine check early handling was added for PowerKVM and we missed to
increment the MCE count in the early handler.

We also increment mce counters in the machine_check_exception call, but
in most cases where we handle the error hypervisor never reaches there
unless its fatal and we want to crash. Only during fatal situation we may
see double increment of mce count. We need to fix that. But for
now it always good to have some count increased instead of zero.
Signed-off-by: NMahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Currently machine check handler does not check for stack overflow for
nested machine check. If we hit another MCE while inside the machine check
handler repeatedly from same address then we get into risk of stack
overflow which can cause huge memory corruption. This patch limits the
nested MCE level to 4 and panic when we cross level 4.
Signed-off-by: NMahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Current code does not check for unhandled/unrecovered errors and return from
interrupt if it is recoverable exception which in-turn triggers same machine
check exception in a loop causing hypervisor to be unresponsive.

This patch fixes this situation and forces hypervisor to panic for
unhandled/unrecovered errors.

This patch also fixes another issue where unrecoverable_exception routine
was called in real mode in case of unrecoverable exception (MSR_RI = 0).
This causes another exception vector 0x300 (data access) during system crash
leading to confusion while debugging cause of the system crash.

Also turn ME bit off while going down, so that when another MCE is hit during
panic path, system will checkstop and hypervisor will get restarted cleanly
by SP.

With the above fixes we now throw correct console messages (see below) while
crashing the system in case of unhandled/unrecoverable machine checks.

--------------
Severe Machine check interrupt [[Not recovered]
  Initiator: CPU
  Error type: UE [Instruction fetch]
    Effective address: 0000000030002864
Oops: Machine check, sig: 7 [#1]
SMP NR_CPUS=2048 NUMA PowerNV
Modules linked in: bork(O) bridge stp llc kvm [last unloaded: bork]
CPU: 36 PID: 55162 Comm: bash Tainted: G           O 3.14.0mce #1
task: c000002d72d022d0 ti: c000000007ec0000 task.ti: c000002d72de4000
NIP: 0000000030002864 LR: 00000000300151a4 CTR: 000000003001518c
REGS: c000000007ec3d80 TRAP: 0200   Tainted: G           O  (3.14.0mce)
MSR: 9000000000041002 <SF,HV,ME,RI>  CR: 28222848  XER: 20000000
CFAR: 0000000030002838 DAR: d0000000004d0000 DSISR: 00000000 SOFTE: 1
GPR00: 000000003001512c 0000000031f92cb0 0000000030078af0 0000000030002864
GPR04: d0000000004d0000 0000000000000000 0000000030002864 ffffffffffffffc9
GPR08: 0000000000000024 0000000030008af0 000000000000002c c00000000150e728
GPR12: 9000000000041002 0000000031f90000 0000000010142550 0000000040000000
GPR16: 0000000010143cdc 0000000000000000 00000000101306fc 00000000101424dc
GPR20: 00000000101424e0 000000001013c6f0 0000000000000000 0000000000000000
GPR24: 0000000010143ce0 00000000100f6440 c000002d72de7e00 c000002d72860250
GPR28: c000002d72860240 c000002d72ac0038 0000000000000008 0000000000040000
NIP [0000000030002864] 0x30002864
LR [00000000300151a4] 0x300151a4
Call Trace:
Instruction dump:
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
---[ end trace 7285f0beac1e29d3 ]---

Sending IPI to other CPUs
IPI complete
OPAL V3 detected !
--------------
Signed-off-by: NMahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

As Ben suggested, it's meaningful to dump PE's location code
for site engineers when hitting EEH errors. The patch introduces
function eeh_pe_loc_get() to retireve the location code from
dev-tree so that we can output it when hitting EEH errors.

If primary PE bus is root bus, the PHB's dev-node would be tried
prior to root port's dev-node. Otherwise, the upstream bridge's
dev-node of the primary PE bus will be check for the location code
directly.
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

This patch enables POWER8 doorbell IPIs on powernv.

Since doorbells can only IPI within a core, we test to see when we can use
doorbells and if not we fall back to XICS.  This also enables hypervisor
doorbells to wakeup us up from nap/sleep via the LPCR PECEDH bit.

Based on tests by Anton, the best case IPI latency between two threads dropped
from 894ns to 512ns.
Signed-off-by: NMichael Neuling <mikey@neuling.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

On PowerNV platform, EEH errors are reported by IO accessors or poller
driven by interrupt. After the PE is isolated, we won't produce EEH
event for the PE. The current implementation has possibility of EEH
event lost in this way:

The interrupt handler queues one "special" event, which drives the poller.
EEH thread doesn't pick the special event yet. IO accessors kicks in, the
frozen PE is marked as "isolated" and EEH event is queued to the list.
EEH thread runs because of special event and purge all existing EEH events.
However, we never produce an other EEH event for the frozen PE. Eventually,
the PE is marked as "isolated" and we don't have EEH event to recover it.

The patch fixes the issue to keep EEH events for PEs that have been
marked as "isolated" with the help of additional "force" help to
eeh_remove_event().
Reported-by: NRolf Brudeseth <rolfb@us.ibm.com>
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Commit b0d278b7 ("powerpc/perf_event: Reduce latency of calling
perf_event_do_pending") added a check for CONFIG_PMAC were a check for
CONFIG_PPC_PMAC was clearly intended.

Fixes: b0d278b7 ("powerpc/perf_event: Reduce latency of calling perf_event_do_pending")
Signed-off-by: NPaul Bolle <pebolle@tiscali.nl>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Commit cd64d169 ("powerpc: mtmsrd not defined") added a check for
CONFIG_PPC_CPU were a check for CONFIG_PPC_FPU was clearly intended.

Fixes: cd64d169 ("powerpc: mtmsrd not defined")
Signed-off-by: NPaul Bolle <pebolle@tiscali.nl>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Commit cb5b242c ("powerpc/eeh: Escalate error on non-existing PE")
escalates the frozen state on non-existing PE to fenced PHB. It
was to improve kdump reliability. After that, commit 361f2a2a
("powrpc/powernv: Reset PHB in kdump kernel") was introduced to
issue complete reset on all PHBs to increase the reliability of
kdump kernel.

Commit cb5b242c becomes unuseful and it would be reverted.
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

When we have the corner case of frozen parent and child PE at the
same time, we have to handle the frozen parent PE prior to the
child. Without clearning the frozen state on parent PE, the child
PE can't be recovered successfully.

The patch searches the EEH PE hierarchy tree and returns the toppest
frozen PE to be handled. It ensures the frozen parent PE will be
handled prior to child PE.
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Since commit cb523e09 ("powerpc/eeh: Avoid I/O access during PE
reset"), the PE is kept as frozen state on hardware level until
the PE reset is done completely. After that, we explicitly clear
the frozen state of the affected PE. However, there might have
frozen child PEs of the affected PE and we also need clear their
frozen state as well. Otherwise, the recovery is going to fail.
Signed-off-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

We've already dropped the default pseries timeout to 10s, do
the same for powernv.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

This makes sure format strings cannot leak into printk (the string has
already been correctly processed for format arguments).
Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

In commit 330a1eb7 "Core EBB support for 64-bit book3s" I messed up
clear_task_ebb(). It clears some but not all of the task's Event Based
Branch (EBB) registers when we duplicate a task struct.

That allows a child task to observe the EBBHR & EBBRR of its parent,
which it should not be able to do.

Fix it by clearing EBBHR & EBBRR.
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
Cc: stable@vger.kernel.org [v3.11+]
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

memory_return_from_buffer returns a signed value, so ret should be
ssize_t.

Fixes the following issue reported by David Binderman:

  [linux-3.15/arch/powerpc/platforms/powernv/opal-msglog.c:65]: (style)
  Checking if unsigned variable 'ret' is less than zero.
  [linux-3.15/arch/powerpc/platforms/powernv/opal-msglog.c:82]: (style)
  Checking if unsigned variable 'ret' is less than zero.

  Local variable "ret" is of type size_t. This is always unsigned,
  so it is pointless to check if it is less than zero.

  https://bugzilla.kernel.org/show_bug.cgi?id=77551

Fixing this exposes a real bug for the case where the entire count
bytes is successfully read from the POS_WRAP case. The second
memory_read_from_buffer will return EINVAL, causing the entire read to
return EINVAL to userspace, despite the data being copied correctly. The
fix is to test for the case where the data has been read and return
early.
Signed-off-by: NJoel Stanley <joel@jms.id.au>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The SPUFS_CNTL_MAP_SIZE define is cut and pasted twice so we can delete
the second instance.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NJeremy Kerr <jk@ozlabs.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

The FCC_GFMR_TTX define is cut and pasted twice so we can remove the
second instance.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

EEH information fetched from OPAL need fix before using in LE environment.
To be included in sparse's endian check, declare them as __beXX and
access them by accessors.

Cc: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NGuo Chao <yan@linux.vnet.ibm.com>
Acked-by: NGavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Everyone can write to these files, which is not what we want.

Cc: stable@vger.kernel.org # 3.15
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Build throws following errors when CONFIG_SMP=n
arch/powerpc/platforms/powernv/subcore.c: In function ‘cpu_update_split_mode’:
arch/powerpc/platforms/powernv/subcore.c:274:15: error: ‘setup_max_cpus’ undeclared (first use in this function)
arch/powerpc/platforms/powernv/subcore.c:285:5: error: lvalue required as left operand of assignment

'setup_max_cpus' variable is relevant only on SMP, so there is no point
working around it for UP. Furthermore, subcore itself is relevant only
on SMP and hence the better solution is to exclude subcore.o and
subcore-asm.o for UP builds.
Signed-off-by: NShreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Reviewed-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Build throws following errors when CONFIG_SMP=n
arch/powerpc/platforms/powernv/setup.c: In function ‘pnv_kexec_wait_secondaries_down’:
arch/powerpc/platforms/powernv/setup.c:179:4: error: implicit declaration of function ‘get_hard_smp_processor_id’
    rc = opal_query_cpu_status(get_hard_smp_processor_id(i),

The usage of get_hard_smp_processor_id() needs the declaration from
<asm/smp.h>. The file setup.c includes <linux/sched.h>, which in-turn
includes <linux/smp.h>. However, <linux/smp.h> includes <asm/smp.h>
only on SMP configs and hence UP builds fail.

Fix this by directly including <asm/smp.h> in setup.c unconditionally.
Reported-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: NSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: NShreyas B. Prabhu <shreyas@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

OPAL will mark a CPU that is guarded as "bad" in the status property of the CPU
node.

Unfortunatley Linux doesn't check this property and will put the bad CPU in the
present map.  This has caused hangs on booting when we try to unsplit the core.

This patch checks the CPU is avaliable via this status property before putting
it in the present map.
Signed-off-by: NMichael Neuling <mikey@neuling.org>
Tested-by: NAnton Blanchard <anton@samba.org>
cc: stable@vger.kernel.org
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

Correct the DSCR SPR becoming temporarily corrupted if a task is
context switched during a transaction.

The problem occurs while suspending the task and is caused by saving
the DSCR to thread.dscr after it has already been set to the CPU's
default value:

__switch_to() calls __switch_to_tm()
	which calls tm_reclaim_task()
	which calls tm_reclaim_thread()
	which calls tm_reclaim()
		where the DSCR is set to the CPU's default
__switch_to() calls _switch()
		where thread.dscr is set to the DSCR

When the task is resumed, it's transaction will be doomed (as usual)
and the DSCR SPR will be corrupted, although the checkpointed value
will be correct. Therefore the DSCR will be immediately corrected by
the transaction aborting, unless it has been suspended. In that case
the incorrect value can be seen by the task until it resumes the
transaction.

The fix is to treat the DSCR similarly to the TAR and save it early
in __switch_to().

A program exposing the problem is added to the kernel self tests as:
tools/testing/selftests/powerpc/tm/tm-resched-dscr.
Signed-off-by: NSam Bobroff <sam.bobroff@au1.ibm.com>
CC: <stable@vger.kernel.org> [v3.10+]
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>