kernel/linux.git/arch/s390/include/asm/alternative.h, branch linux-7.0.y

s390: Replace ASSEMBLY with ASSEMBLER in non-uapi headers

2025-06-16T14:23:02+00:00

While the GCC and Clang compilers already define __ASSEMBLER__ automatically when compiling assembler code, __ASSEMBLY__ is a macro that only gets defined by the Makefiles in the kernel. This is bad since macros starting with two underscores are names that are reserved by the C language. It can also be very confusing for the developers when switching between userspace and kernelspace coding, or when dealing with uapi headers that rather should use __ASSEMBLER__ instead. So let's now standardize on the __ASSEMBLER__ macro that is provided by the compilers. This is a completely mechanical patch (done with a simple "sed -i" statement), with some manual fixups done later while rebasing the patch. Signed-off-by: Thomas Huth Acked-by: Heiko Carstens Link: https://lore.kernel.org/r/20250611140046.137739-3-thuth@redhat.com Signed-off-by: Alexander Gordeev

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/alternatives: Remove ALT_FACILITY_EARLY

2024-09-13T15:28:36+00:00

Patch all alternatives which depend on facilities from the decompressor. There is no technical reason which enforces to split patching of such alternatives to the decompressor and the kernel. This simplifies alternative handling a bit, since one alternative type is removed. Signed-off-by: Heiko Carstens Signed-off-by: Jason A. Donenfeld

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: Merge both alternative header files

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

The two alternative header files must stay in sync. This is easier to achieve within one header file. Therefore merge both of them and have only one file, like most other architectures. Reviewed-by: Alexander Gordeev Tested-by: Sven Schnelle Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik

kernel/linux.git/arch/s390/include/asm/alternative.h, branch linux-7.0.y

s390: Replace __ASSEMBLY__ with __ASSEMBLER__ in non-uapi headers

s390/lowcore: Convert relocated lowcore alternative to machine feature

s390: Static branches for machine features infrastructure

s390/alternatives: Remove ALT_FACILITY_EARLY

s390: Add infrastructure to patch lowcore accesses

s390/alternatives: Remove alternative facility list

s390/nospec: Push down alternative handling

s390/alternatives: Allow early alternative patching in decompressor

s390/alternatives: Rework to allow for callbacks

s390/alternatives: Merge both alternative header files

s390: Replace ASSEMBLY with ASSEMBLER in non-uapi headers