The identity mapping position in virtual memory is randomized
together with the kernel mapping. That position can never
overlap with the lowcore even when the lowcore is relocated.

Prevent overlapping with the lowcore to allow independent
positioning of the identity mapping. With the current value
of the alternative lowcore address of 0x70000 the overlap
could happen in case the identity mapping is placed at zero.

This is a prerequisite for uncoupling of randomization base
of kernel image and identity mapping in virtual memory.

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

The s390 architecture defines two special per-CPU data pages
called the "prefix area". In s390-linux terminology this is usually
called "lowcore". This memory area contains system configuration
data like old/new PSW's for system call/interrupt/machine check
handlers and lots of other data. It is normally mapped to logical
address 0. This area can only be accessed when in supervisor mode.

This means that kernel code can dereference NULL pointers, because
accesses to address 0 are allowed. Parts of lowcore can be write
protected, but read accesses and write accesses outside of the write
protected areas are not caught.

To remove this limitation for debugging and testing, remap lowcore to
another address and define a function get_lowcore() which simply
returns the address where lowcore is mapped at. This would normally
introduce a pointer dereference (=memory read). As lowcore is used
for several very often used variables, add code to patch this function
during runtime, so we avoid the memory reads.

For C code get_lowcore() has to be used, for assembly code it is
the GET_LC macro. When using this macro/function a reference is added
to alternative patching. All these locations will be patched to the
actual lowcore location when the kernel is booted or a module is loaded.

To make debugging/bisecting problems easier, this patch adds all the
infrastructure but the lowcore address is still hardwired to 0. This
way the code can be converted on a per function basis, and the
functionality is enabled in a patch after all the functions have
been converted.

Note that this requires at least z16 because the old lpsw instruction
only allowed a 12 bit displacement. z16 introduced lpswey which allows
20 bits (signed), so the lowcore can effectively be mapped from
address 0 - 0x7e000. To use 0x7e000 as address, a 6 byte lgfi
instruction would have to be used in the alternative. To save two
bytes, llilh can be used, but this only allows to set bits 16-31 of
the address. In order to use the llilh instruction, use 0x70000 as
alternative lowcore address. This is still large enough to catch
NULL pointer dereferences into large arrays.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

The alternative and the normal facility list are always identical. Remove
the alternative facility list, which allows to simplify the alternatives
code.

Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Tested-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

To allow testing flags for offline CPUs, move the CIF flags
to struct pcpu. To avoid having to calculate the array index
for each access, add a pointer to the pcpu member for the current
cpu to lowcore.

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

The struct vm_layout contains fields used in __pa/__va calculations. Such
fundamental things have to be exported with EXPORT_SYMBOL to avoid
breakages of out-of-tree modules under non-GPL licenses.

Fixes: 7de0446f0b26 ("s390/boot: Make identity mapping base address explicit")
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Replace all S390_lowcore usages in arch/s390/ by get_lowcore().

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

It is nowhere used in the decompressor, therefore remove it.

Fixes: 17e89e1340a3 ("s390/facilities: move stfl information from lowcore to global data")
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

This is a preparatory rework to allow uncoupling virtual
and physical addresses spaces.

Introduce .amode31 section address range AMODE31_START
and AMODE31_END macros for later use.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

This is a preparatory rework to allow uncoupling virtual
and physical addresses spaces.

Currently the identity mapping base address is implicit
and is always set to zero. Make it explicit by putting
into __identity_base persistent boot variable and use it
in proper context - which is the value of PAGE_OFFSET.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

This is a preparatory rework to allow uncoupling virtual
and physical addresses spaces.

Put virtual memory layout information into a structure
to improve code generation when accessing the structure
members, which are currently only ident_map_size and
__kaslr_offset.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>