Detect and report the etoken facility. With spectre_v2=auto or
CONFIG_EXPOLINE_AUTO=y automatically disable expolines and use
the full branch prediction mode for the kernel.
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Remove attribute packed where possible failing this add proper alignment
information to fix warnings like the one below:

drivers/s390/cio/chsc.c: In function 'chsc_siosl':
drivers/s390/cio/chsc.c:1287:2: warning: alignment 1 of 'struct <anonymous>' is less than 4 [-Wpacked-not-aligned]
  } __attribute__ ((packed)) *siosl_area;

Note: this patch should be a nop since non of these structs use auto
storage but allocated pages. However there are changes to the generated
code because of additional padding at the end of some of the structs due
to alignment when memset(foo, 0, sizeof(*foo)) is used.
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Both css_evaluate_new_subchannel and cio_validate_subchannel used
stsch and css_sch_is_valid to check for a valid device.

Reduce stsch calls during subchannel evaluation by re-using schib
data. Also the type/devno valid information is only checked once.
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Reviewed-by: NPeter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

In css_alloc_subchannel we allocate the subchannel and do a
validation of the subchannel (to decide if we should look for
devices via this subchannel). On a typical LPAR we find lots
of subchannels to be invalid (because there is no device
attached or the device is blacklisted) leading to lots of
useless kmalloc and kfree calls.

This patch changes the order to only allocate the subchannels
that have been found valid.
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Reviewed-by: NPeter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

The css bus code uses 2 initcalls: channel_subsystem_init to
initialize internal data and channel_subsystem_init_sync to
start scanning for devices and wait for it to finish.

The start scanning for devices part is moved to the first
initcall such that more work happens in parallel.
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Improve locking in chp_new to make sure that we don't register
the same chpid twice. Chpid registration was synchronized via
the machine check handler thread but we also have codepaths to
look for new chpids triggered independent of that thread (during
IPL or resume from hibernate).
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Reviewed-by: NPeter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

When the oom killer kills a userspace process in the page fault handler
while in guest context, the fault handler fails to release the mm_sem
if the FAULT_FLAG_RETRY_NOWAIT option is set. This leads to a deadlock
when tearing down the mm when the process terminates. This bug can only
happen when pfault is enabled, so only KVM clients are affected.

The problem arises in the rare cases in which handle_mm_fault does not
release the mm_sem. This patch fixes the issue by manually releasing
the mm_sem when needed.

Fixes: 24eb3a82 ("KVM: s390: Add FAULT_FLAG_RETRY_NOWAIT for guest fault")
Cc: <stable@vger.kernel.org> # 3.15+
Signed-off-by: NClaudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

cmm_set_timer could be called concurrently from cmm_thread, cmm proc
handler, upon cmm smsg receive and timer function itself. To avoid
potential race condition and hitting BUG_ON in add_timer on already
pending timer simply reuse mod_timer which is according to
documentation "the only safe way to modify the timeout" with multiple
unserialized concurrent users. mod_timer can handle both active and
inactive timers which allows to carry out minor code simplification as
well.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Replace strncpy which is used to deliberately avoid string NUL-termination
with memcpy. This allows to get rid of gcc 8 stringop-truncation warning:

    inlined from 'query_crypto_facility.constprop' at
    drivers/s390/crypto/pkey_api.c:702:2:
./include/linux/string.h:246:9: warning: '__builtin_strncpy' output
truncated before terminating nul copying 8 bytes from a string of the
same length [-Wstringop-truncation]
Reviewed-by: NHarald Freudenberger <freude@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

I am leaving IBM and will move on to other working area,
so remove myself as a vfio-ccw maintainer.
Signed-off-by: NDong Jia Shi <bjsdjshi@linux.ibm.com>

Message-Id: <20180706015743.41810-1-bjsdjshi@linux.ibm.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Simplify appldata proc handlers by reusing generic proc handler functions.
Tested-by: NGerald Schaefer <gerald.schaefer@de.ibm.com>
Reviewed-by: NGerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Split cmm_pages_handler into cmm_pages_handler and
cmm_timed_pages_handler, each handling separate proc entry.  And reuse
proc_doulongvec_minmax to simplify proc handlers. Min/max values are
optional and are omitted here.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Reuse proc_douintvec_minmax to simplify topology mode proc handler.
This also enforces correct range of 0-1 on proc writes and correctly
handles numbers starting with 0 or spaces.

Before:
$ echo 01 > /proc/sys/s390/topology
$ cat /proc/sys/s390/topology
0
$ echo ' 1' > /proc/sys/s390/topology
-bash: echo: write error: Invalid argument
$ echo 2 > /proc/sys/s390/topology
-bash: echo: write error: Invalid argument
$ echo 12 > /proc/sys/s390/topology
$ cat /proc/sys/s390/topology
1

After:
$ echo 01 > /proc/sys/s390/topology
$ cat /proc/sys/s390/topology
1
$ echo ' 1' > /proc/sys/s390/topology
$ cat /proc/sys/s390/topology
1
$ echo 2 > /proc/sys/s390/topology
-bash: echo: write error: Invalid argument
$ echo 12 > /proc/sys/s390/topology
-bash: echo: write error: Invalid argument
$ echo '   0' > /proc/sys/s390/topology
$ cat /proc/sys/s390/topology
0
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Reuse generic proc_dointvec_minmax proc handler instead of
proc_handler_callhome.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Since proc_dointvec does not perform value range control,
proc_dointvec_minmax should be used to limit value range, which is
clearly intended here, as the internal representation of the value:

unsigned int alloc_pgste:1;

In fact it currently works, since we have

      mm->context.alloc_pgste = page_table_allocate_pgste || ...

... since commit 23fefe11 ("s390/kvm: avoid global config of vm.alloc_pgste=1")

Before that it was

       mm->context.alloc_pgste = page_table_allocate_pgste;

which was broken. That was introduced with commit 0b46e0a3 ("s390/kvm:
remove delayed reallocation of page tables for KVM").

Fixes: 0b46e0a3 ("s390/kvm: remove delayed reallocation of page tables for KVM")
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Currently there are some variables in the purgatory (e.g. kernel_entry)
which are defined twice, once in assembler- and once in c-code. The reason
for this is that these variables are set during purgatory load, where
sanity checks on the corresponding Elf_Sym's are made, while they are used
in assembler-code. Thus adding a second definition in c-code is a handy
workaround to guarantee correct Elf_Sym's are created.

When the purgatory is compiled with -fcommon (default for gcc on s390) this
is no problem because both symbols are merged by the linker. However this
is not required by ISO C and when the purgatory is built with -fno-common
the linker fails with errors like

arch/s390/purgatory/purgatory.o:(.bss+0x18): multiple definition of `kernel_entry'
arch/s390/purgatory/head.o:/.../arch/s390/purgatory/head.S:230: first defined here

Thus remove the duplicate definitions and add the required size and type
information to the assembler definition. Also add -fno-common to the
command line options to prevent similar hacks in the future.
Signed-off-by: NPhilipp Rudo <prudo@linux.ibm.com>
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Without FORCE make does not detect changes only made to the command line
options. So object files might not be re-built even when they should be.
Fix this by adding FORCE where it is missing.

Fixes: 840798a1 ("s390/kexec_file: Add purgatory")
Cc: <stable@vger.kernel.org> # 4.17
Signed-off-by: NPhilipp Rudo <prudo@linux.ibm.com>
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

When the kernel is built with CONFIG_EXPOLINE=y and a compiler with
indirect branch mitigation enabled the purgatory crashes. The reason for
that is that the macros defined for expoline are used in mem.S. These
macros define new sections (.text.__s390x_indirect_*) which are marked
executable. Due to the missing linker script those sections are linked to
address 0, just as the .text section. In combination with the entry point
also being at address 0 this causes the purgatory load code
(kernel/kexec_file.c: kexec_purgatory_setup_sechdrs) to update the entry
point twice. Thus the old kernel jumps to some 'random' address causing the
crash.

To fix this turn off expolines for the purgatory. There is no problem with
this in this case due to the fact that the purgatory only runs once and the
tlb is purged (diag 308) in the end.

Fixes: 840798a1 ("s390/kexec_file: Add purgatory")
Cc: <stable@vger.kernel.org> # 4.17
Signed-off-by: NPhilipp Rudo <prudo@linux.ibm.com>
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

In the quest to remove all stack VLA usage from the kernel[1], this moves
the "$#" replacement from being an argument to being inside the function,
which avoids generating VLAs.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.comSigned-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Change the tasklets parameter type to fix W=1 warnings when building
with gcc 8 like below:

drivers/s390/block/dasd.c: In function 'dasd_alloc_device':
drivers/s390/block/dasd.c:129:8: warning: cast between incompatible function types
from 'void (*)(struct dasd_device *)' to 'void (*)(long unsigned int)' [-Wcast-function-type]
        (void (*)(unsigned long)) dasd_device_tasklet,
        ^
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Acked-by: NJan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Add support for format 3 function measurement blocks.
Signed-off-by: NSebastian Ott <sebott@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Since decompressor cflags and aflags are made from scratch add extra
debug flags when CONFIG_DEBUG_INFO is enabled.

Also adds support for CONFIG_DEBUG_INFO_DWARF4 option.
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Adding *.o.chkbss files to targets list makes sure that the kbuild is
aware of them and removes them during make clean.

Also remove *.o.chkbss file before an actual check, to avoid having
stale *.o.chkbss file left even if the check is failed.
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

startup.a build rule packs a list of prerequisites into archive. That
didn't take into account extra prerequisites added by chkbss, so that
zero length *.o.chkbss files were also packed into the archive.

To avoid that filter only real object from prerequisites list.
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Correct merging error which replaced startup.a in targets list with
non-existing setup.a. Due to missing startup.a in targets list if_changed
triggered startup.a rebuild unconditionally.

Fixes: 3e200c54438d ("s390/decompressor: avoid reusing uncompressed image objects")
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Get rid of this compile warning for !PROC_FS:

  CC      arch/s390/kernel/sysinfo.o
arch/s390/kernel/sysinfo.c:275:12: warning: 'sysinfo_show' defined but not used [-Wunused-function]
 static int sysinfo_show(struct seq_file *m, void *v)
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Replace strncpy which has been used to copy a substring into buf
without NUL-termination with memcpy to avoid the following gcc 8
warnings:

arch/s390/tools/gen_opcode_table.c: In function ‘add_to_group.isra.4’:
arch/s390/tools/gen_opcode_table.c:260:2: warning: ‘strncpy’
output may be truncated copying 2 bytes from a string of length 19
[-Wstringop-truncation]
  strncpy(group->opcode, insn->opcode, 2);

In function ‘print_opcode_table’,
    inlined from ‘main’ at arch/s390/tools/gen_opcode_table.c:333:2:
arch/s390/tools/gen_opcode_table.c:286:4: warning: ‘strncpy’
output may be truncated copying 2 bytes from a string of length 19
[-Wstringop-truncation]
    strncpy(opcode, insn->opcode, 2);
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Since the plain vmlinux ELF file no longer carries all necessary parts
for starting up (like the entry point and decompressor), add a check
which would block boot process and encourage users to use bzImage or
arch/s390/boot/compressed/vmlinux instead.

The check relies on s390 linux entry point ABI definition, which is only
present in bzImage and arch/s390/boot/compressed/vmlinux.
Reported-by: NGuenter Roeck <linux@roeck-us.net>
Tested-by: NGuenter Roeck <linux@roeck-us.net>
Acked-by: NCornelia Huck <cohuck@redhat.com>
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

The following gcc warning is issued for strncpy which is used to
deliberately avoid string NUL-termination. Reuse memcpy to avoid the
warning.

    inlined from 'monwrite_diag' at drivers/s390/char/monwriter.c:64:2:
./include/linux/string.h:246:9: warning: '__builtin_strncpy' output
truncated before terminating nul copying 7 bytes from a string of the
same length [-Wstringop-truncation]
Reviewed-by: NGerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Replace strncpy which is used to deliberately avoid string NUL-termination
with memcpy. This allows to get rid of gcc 8 stringop-truncation warning:

    inlined from 'ext_to_int_kekl' at drivers/s390/char/tape_3590.c:123:2:
./include/linux/string.h:246:9: warning: '__builtin_strncpy'
output may be truncated copying 64 bytes from a string of length 64
[-Wstringop-truncation]

Also replaces "for" loop on memset.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Use strlcpy to make sure strings are NUL-terminated. Fixes the following
gcc 8 warning:

inlined from 'register_tape_dev' at drivers/s390/char/tape_class.c:57:2:
./include/linux/string.h:246:9: warning: '__builtin_strncpy' specified
bound 32 equals destination size [-Wstringop-truncation]
Acked-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Aligning struct lowcore to double page size allows to get rid of this
gcc warning:

In file included from ./arch/s390/include/asm/setup.h:56,
                 from ./arch/s390/include/asm/page.h:36,
                 from ./arch/s390/include/asm/user.h:11,
                 from ./include/linux/user.h:1,
                 from ./include/linux/elfcore.h:5,
                 from ./include/linux/crash_core.h:6,
                 from ./include/linux/kexec.h:18,
                 from arch/s390/purgatory/purgatory.c:10:
./arch/s390/include/asm/lowcore.h:189:1: warning: alignment 1 of 'struct
lowcore' is less than 8 [-Wpacked-not-aligned]
 } __packed;
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

The following linker construct is problematic with linkers of
binutils < 2.28:

EXCLUDE_FILE (*piggy.o) *(.rodata.*)

from 8f1732fc2a11dc of binutils:
"though the linker accepts this without complaint the
EXCLUDE_FILE part is silently ignored and has no effect."

Silent ignoring of EXCLUDE_FILE construct made .rodata.compressed be
part of .rodata, and in case of .rodata.compressed following some
unaligned data, input_len would also become unaligned.

from arch/s390/boot/compressed/vmlinux.map:
 .rodata.compressed
                0x0000000000012fea   0x4d57e7 arch/s390/boot/compressed/piggy.o
                0x0000000000012fea                input_len
                0x0000000000012fee                input_data

input_len is later used here:
arch/s390/boot/compressed/misc.c:113
	__decompress(input_data, input_len, NULL, NULL, output, 0, NULL, error);

asm generated by gcc looks like:
	.loc 3 113 0
egfrl	%r11,input_len

from what assembler generates invalid (the second operand must be aligned
on a doubleword boundary):
   0x00000000000129b4 <+148>:   c4 bc 00 00 03 1b       lgfrl   %r11,0x12fea
hence specification exception is recognized.

To avoid an issue use EXCLUDE_FILE construct which is recognized by
older linkers (since at least binutils-2_11)
	*(EXCLUDE_FILE (*piggy.o) .rodata.compressed)

Also ensure that .rodata.compressed is at least doubleword aligned.

Fixes: 89b5202e ("s390/decompressor: support uncompressed kernel")
Reported-by: NHalil Pasic <pasic@linux.ibm.com>
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Since the uncompressed image .text section starts at 0x100000 now there
is no need to redefine _text to something else to make perf happy.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Avoid unnecessary rewrite of psw and merge _stext into
startup_continue. This allows to move _stext definition to vmlinux.lds.S,
where _etext is also defined and set _stext to the actual beginning of
.text at 0x100000.

This fixes the problem with setting the last .text page as
not-executable due to vmem_map_init relying on page alinged _stext and
_etext.

Fixes: bd79d663 ("s390/decompressor: trim the kernel image up to 1M")
Reported-by: NNils Hoppmann <niho@de.ibm.com>
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Instead of generating uncompressed kernel image starting at 0, filling
first mb with zeros (with ".org 0x100000") and then trimming it off
from vmlinux.bin before compression, simply generate a kernel image
starting from 0x100000.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Since startup code now reserves memory ranges [0, PARMAREA_END] and
[_stext, <end of kernel>] _ehead symbol is not used and could be
cleaned up.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

Currently none of the vmlinux linker script patterns in .text section
match expoline execute-trampolines, and they end up as separate
sections:
.text.__s390_indirect_jump_r1,
.text.__s390x_indirect_jump_r1use_r9,
.text.__s390x_indirect_branch_4_1use_6, ...

Add a pattern to match them all.
Reviewed-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

___kcrctab section is not used during the decompressor phase and could be
discarded to save the memory. It is currently generated due to lib/mem.S
usage, which exports few symbols.
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

There have been identified some places in the zcrypt
device driver where copy_from_user() is called but the
length value is not explicitly checked.

So now some plausibility checks and comments have been
introduced there.
Signed-off-by: NHarald Freudenberger <freude@linux.ibm.com>
Acked-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>