linux-stable.git/arch/s390/kernel/alternative.c, branch linux-rolling-stable

kernel.h: drop hex.h and update all hex.h users

2026-01-21T03:44:19+00:00

Remove  from  and update all users/callers of
hex.h interfaces to directly #include  as part of the process
of putting kernel.h on a diet.

Removing hex.h from kernel.h means that 36K C source files don't have to
pay the price of parsing hex.h for the roughly 120 C source files that
need it.

This change has been build-tested with allmodconfig on most ARCHes.  Also,
all users/callers of  in the entire source tree have been
updated if needed (if not already #included).

Link: https://lkml.kernel.org/r/20251215005206.2362276-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap 
Reviewed-by: Andy Shevchenko 
Cc: Ingo Molnar 
Cc: Yury Norov (NVIDIA) 
Signed-off-by: Andrew Morton

s390/alternatives: Add debug functionality

2025-03-04T16:18:08+00:00

Similar to x86 and loongarch add a "debug-alternative" command line
parameter, which allows for alternative debugging. The parameter
itself comes with architecture specific semantics:

"debug-alternative"
 -> print debug message for every single alternative

"debug-alternative=0;2"
-> print debug message for all alternatives with type 0 and 2

"debug-alternative=0:0-7"
-> print debug message for all alternatives with type 0 which have a
   facility number within the range of 0-7

"debug-alternative=0:!8;1"
-> print debug message for all alternatives with type 0, for all
   facility numbers, except facility 8, and in addition print all
   alternatives with type 1

A defconfig build currently results in a kernel with more than 20.000
alternatives, where the majority is for the niai alternative (spinlocks),
and the relocated lowcore alternative. The following kernel command like
options limit alternative debug output, and enable dynamic debug messages:

debug-alternative=0:!49;1:!0
earlyprintk
bootdebug
ignore_loglevel
loglevel=8
dyndbg="file alternative.c +p"

This results in output like this:

 alt: [0/ 11] 0000021b9ce8680c: c0f400000089 -> c00400000000
 alt: [0/ 64] 0000021b9ce87e60: c0f400000043 -> c00400000000
 alt: [0/133] 0000021b9ce88c56: c0f400000027 -> c00400000000
 alt: [0/ 74] 0000021b9ce89410: c0f40000002a -> c00400000000
 alt: [0/ 40] 0000021b9dc3720a: 47000000 -> b280d398
 alt: [0/193] 0000021b9dc37306: 47000000 -> b201d2b0
 alt: [0/193] 0000021b9dc37354: c00400000000 -> d20720c0d2b0
 alt: [1/  5] 0000038d720d7bf2: c0f400000016 -> c00400000000

With

[/]  oldcode -> newcode

Alternative data depends on the alternative type: for type 0
(ALT_TYPE_FACILITY) data is the facility. For type 1 (ALT_TYPE_FEATURE)
data is the corresponding machine feature.

Acked-by: Vasily Gorbik 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390/lowcore: Convert relocated lowcore alternative to machine feature

2025-03-04T16:18:05+00:00

Convert the explicit relocated lowcore alternative type to a more
generic machine feature. This only reduces the number of alternative
types, but has no impact on code generation.

Reviewed-by: Vasily Gorbik 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390: Static branches for machine features infrastructure

2025-03-04T16:18:05+00:00

Provide infrastructure which allows to generate machine_has_()
functions, which are replacing the existing MACHINE_HAS_ macros.
Such function usages generate a static branch depending on . The
static branch is patched using an alternative.

Each  correlates with a bit set in the machine_features bit
field. If the corresponding bit is set, the branch will be patched. In
order to have any effect on branch patching feature bits must be set with
set_machine_features() in the decompressor before alternatives patching of
the kernel image.

It is possible to use clear_machine_feature() and test_machine_feature()
for machine features which cannot be completely detected within the
decompressor, e.g. if common code command line parameters allow to enable
or disable certain features. In such cases test_machine_feature() instead
of machine_has_feature() must be used within the kernel. This results in a
runtime check and not a static branch.

Reviewed-by: Vasily Gorbik 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390: Add infrastructure to patch lowcore accesses

2024-07-23T14:02:32+00:00

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 
Signed-off-by: Sven Schnelle 
Signed-off-by: Vasily Gorbik

s390/alternatives: Remove alternative facility list

2024-07-23T14:02:31+00:00

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 
Tested-by: Sven Schnelle 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390/nospec: Push down alternative handling

2024-07-23T14:02:31+00:00

The nospec implementation is deeply integrated into the alternatives
code: only for nospec an alternative facility list is implemented and
used by the alternative code, while it is modified by nospec specific
needs.

Push down the nospec alternative handling into the nospec by
introducing a new alternative type and a specific nospec callback to
decide if alternatives should be applied.

Also introduce a new global nobp variable which together with facility
82 can be used to decide if nobp is enabled or not.

Acked-by: Alexander Gordeev 
Tested-by: Sven Schnelle 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390/alternatives: Allow early alternative patching in decompressor

2024-07-23T14:02:31+00:00

Add the required code to patch alternatives early in the decompressor.
This is required for the upcoming lowcore relocation changes, where
alternatives for facility 193 need to get patched before lowcore
alternatives.

Reviewed-by: Alexander Gordeev 
Co-developed-by: Heiko Carstens 
Signed-off-by: Heiko Carstens 
Signed-off-by: Sven Schnelle 
Signed-off-by: Vasily Gorbik

s390/alternatives: Rework to allow for callbacks

2024-07-23T14:02:31+00:00

Rework alternatives to allow for callbacks. With this every
alternative entry has additional data encoded:

- When (aka context) an alternative is supposed to be applied

- The type of an alternative, which allows for type specific handling
  and callbacks

- Extra type specific payload (patch information), which can be passed
  to callbacks in order to decide if an alternative should be applied
  or not

With this only the "late" context is implemented, which means there is
no change to the previous behaviour. All code is just converted to the
more generic new infrastructure.

Reviewed-by: Alexander Gordeev 
Tested-by: Sven Schnelle 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390/alternatives: Move text sync functions

2024-07-23T14:02:31+00:00

Move all text sync functions from alternative.c to processor.c. This
way there is only minimal code left in alternative.c left, which is a
prerequisite to use the C file within boot code as well.

Reviewed-by: Alexander Gordeev 
Tested-by: Sven Schnelle 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik