kernel.git/arch/s390/include/asm/processor.h, branch linux-6.10.y

s390: Mark psw in __load_psw_mask() as __unitialized

2024-05-14T11:37:08Z

Without __unitialized, the following code is generated when INIT_STACK_ALL_ZERO is enabled: 86: d7 0f f0 a0 f0 a0 xc 160(16,%r15), 160(%r15) 8c: e3 40 f0 a0 00 24 stg %r4, 160(%r15) 92: c0 10 00 00 00 08 larl %r1, 0xa2 98: e3 10 f0 a8 00 24 stg %r1, 168(%r15) 9e: b2 b2 f0 a0 lpswe 160(%r15) The xc is not adding any security because psw is fully initialized with the following instructions. Add __unitialized to the psw definitiation to avoid the superfluous clearing of psw. Reviewed-by: Heiko Carstens Signed-off-by: Sven Schnelle Signed-off-by: Alexander Gordeev

s390/idle: Rewrite psw_idle() in C

2024-05-14T11:37:07Z

To ease maintenance and further enhancements, convert the psw_idle() function to C. Reviewed-by: Heiko Carstens Signed-off-by: Sven Schnelle Signed-off-by: Alexander Gordeev

s390/stackstrace: Detect vdso stack frames

2024-05-14T11:37:07Z

Clear the backchain of the extra stack frame added by the vdso user wrapper code. This allows the user stack walker to detect and skip the non-standard stack frame. Without this an incorrect instruction pointer would be added to stack traces, and stack frame walking would be continued with a more or less random back chain. Fixes: aa44433ac4ee ("s390: add USER_STACKTRACE support") Reviewed-by: Jens Remus Signed-off-by: Heiko Carstens Signed-off-by: Alexander Gordeev

s390/entry: add CIF_SIE flag and remove sie64a() address check

2024-03-17T18:08:49Z

When a program check, interrupt or machine check is triggered, the PSW address is compared to a certain range of the sie64a() function to figure out whether SIE was interrupted and a cleanup of SIE is needed. This doesn't work with kprobes: If kprobes probes an instruction, it copies the instruction to the kprobes instruction page and overwrites the original instruction with an undefind instruction (Opcode 00). When this instruction is hit later, kprobes single-steps the instruction on the kprobes_instruction page. However, if this instruction is a relative branch instruction it will now point to a different location in memory due to being moved to the kprobes instruction page. If the new branch target points into sie64a() the kernel assumes it interrupted SIE when processing the breakpoint and will crash trying to access the SIE control block. Instead of comparing the address, introduce a new CIF_SIE flag which indicates whether SIE was interrupted. Signed-off-by: Sven Schnelle Suggested-by: Heiko Carstens Reviewed-by: Heiko Carstens Signed-off-by: Heiko Carstens

s390/fpu: limit save and restore to used registers

2024-02-16T13:30:16Z

The first invocation of kernel_fpu_begin() after switching from user to kernel context will save all vector registers, even if only parts of the vector registers are used within the kernel fpu context. Given that save and restore of all vector registers is quite expensive change the current approach in several ways: - Instead of saving and restoring all user registers limit this to those registers which are actually used within an kernel fpu context. - On context switch save all remaining user fpu registers, so they can be restored when the task is rescheduled. - Saving user registers within kernel_fpu_begin() is done without disabling and enabling interrupts - which also slightly reduces runtime. In worst case (e.g. interrupt context uses the same registers) this may lead to the situation that registers are saved several times, however the assumption is that this will not happen frequently, so that the new method is faster in nearly all cases. - save_user_fpu_regs() can still be called from all contexts and saves all (or all remaining) user registers to a tasks ufpu user fpu save area. Overall this reduces the time required to save and restore the user fpu context for nearly all cases. Signed-off-by: Heiko Carstens

s390/fpu: remove regs member from struct fpu

2024-02-16T13:30:16Z

KVM was the only user which modified the regs pointer in struct fpu. Remove the pointer and convert the rest of the core fpu code to directly access the save area embedded within struct fpu. Reviewed-by: Claudio Imbrenda Signed-off-by: Heiko Carstens

s390/fpu: make kernel fpu context preemptible

2024-02-16T13:30:15Z

Make the kernel fpu context preemptible. Add another fpu structure to the thread_struct, and use it to save and restore the kernel fpu context if its task uses fpu registers when it is preempted. Reviewed-by: Claudio Imbrenda Signed-off-by: Heiko Carstens

s390/fpu: rename save_fpu_regs() to save_user_fpu_regs(), etc

2024-02-16T13:30:15Z

Rename save_fpu_regs(), load_fpu_regs(), and struct thread_struct's fpu member to save_user_fpu_regs(), load_user_fpu_regs(), and ufpu. This way the function and variable names reflect for which context they are supposed to be used. This large and trivial conversion is a prerequisite for making the kernel fpu usage preemptible. Reviewed-by: Claudio Imbrenda Signed-off-by: Heiko Carstens

s390/fpu: convert FPU CIF flag to regular TIF flag

2024-02-16T13:30:15Z

The FPU state, as represented by the CIF_FPU flag reflects the FPU state of a task, not the CPU it is running on. Therefore convert the flag to a regular TIF flag. This removes the magic in switch_to() where a save_fpu_regs() call for the currently (previous) running task sets the per-cpu CIF_FPU flag, which is required to restore FPU register contents of the next task, when it returns to user space. Signed-off-by: Heiko Carstens

s390/fpu: move, rename, and merge header files

2024-02-16T13:30:14Z

Move, rename, and merge the fpu and vx header files. This way fpu header files have a consistent naming scheme (fpu*.h). Also get rid of the fpu subdirectory and move header files to asm directory, so that all fpu and vx header files can be found at the same location. Merge internal.h header file into other header files, since the internal helpers are used at many locations. so those helper functions are really not internal. Signed-off-by: Heiko Carstens