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

s390/bug: Skip __WARN_trap() in call traces

2026-01-27T11:16:16+00:00

In order to avoid rather pointless warning disassemblies of __WARN_trap()
set the PSW address to the return address of the function which called
__WARN_trap(). This is the address to which __WARN_trap() would return
in any case.

The result is a disassembly of the function which called __WARN_trap(),
which is much more helpful.

Before:

WARNING: arch/s390/kernel/setup.c:1017 at foobar+0x2c/0x20, CPU#0: swapper/0/0
...
Krnl PSW : 0704c00180000000 000003ffe0f675f4 (__WARN_trap+0x4/0x10)
...
Krnl Code: 000003ffe0f675ec: 0707                bcr     0,%r7
           000003ffe0f675ee: 0707                bcr     0,%r7
          *000003ffe0f675f0: af000001            mc      1,0
          >000003ffe0f675f4: 07fe                bcr     15,%r14
           000003ffe0f675f6: 47000700            bc      0,1792
           000003ffe0f675fa: 0707                bcr     0,%r7
           000003ffe0f675fc: 0707                bcr     0,%r7
           000003ffe0f675fe: 0707                bcr     0,%r7
Call Trace:
 [<000003ffe0f675f4>] __WARN_trap+0x4/0x10
 [<000003ffe185bc2e>] arch_cpu_finalize_init+0x26/0x60
 [<000003ffe185654c>] start_kernel+0x53c/0x5d8
 [<000003ffe010002e>] startup_continue+0x2e/0x40

Afterwards:

WARNING: arch/s390/kernel/setup.c:1017 at foobar+0x12/0x30, CPU#0: swapper/0/0
...
Krnl PSW : 0704c00180000000 000003ffe185bc2e (arch_cpu_finalize_init+0x26/0x60)
...
Krnl Code: 000003ffe185bc1c: e3f0ff98ff71        lay     %r15,-104(%r15)
           000003ffe185bc22: e3e0f0980024        stg     %r14,152(%r15)
          *000003ffe185bc28: c0e5ff45ed94        brasl   %r14,000003ffe0119750
          >000003ffe185bc2e: c0e5ffa052b9        brasl   %r14,000003ffe0c661a0
           000003ffe185bc34: c020fffe86d6        larl    %r2,000003ffe182c9e0
           000003ffe185bc3a: e548f0a80006        mvghi   168(%r15),6
           000003ffe185bc40: e548f0a00005        mvghi   160(%r15),5
           000003ffe185bc46: a7690004            lghi    %r6,4
Call Trace:
 [<000003ffe185bc2e>] arch_cpu_finalize_init+0x26/0x60
 [<000003ffe185654c>] start_kernel+0x53c/0x5d8
 [<000003ffe010002e>] startup_continue+0x2e/0x40

Reviewed-by: Sven Schnelle 
Signed-off-by: Heiko Carstens

s390/bug: Implement __WARN_printf()

2026-01-27T11:16:16+00:00

This is the s390 variant of commit 5b472b6e5bd9 ("x86_64/bug: Implement
__WARN_printf()"). See the x86 commit for the general idea; there are only
implementation details which are different.

With the new exception based __WARN_printf() implementation the generated
code for a simple WARN() is simplified.

For example:

void foo(int a) { WARN(a, "bar"); }

Before this change the generated code looks like this:

0000000000000210 :
 210:   c0 04 00 00 00 00       jgnop   210 
 216:   ec 26 00 06 00 7c       cgijne  %r2,0,222 
 21c:   c0 f4 00 00 00 00       jg      21c 
                        21e: R_390_PC32DBL      __s390_indirect_jump_r14+0x2
 222:   eb ef f0 88 00 24       stmg    %r14,%r15,136(%r15)
 228:   b9 04 00 ef             lgr     %r14,%r15
 22c:   e3 f0 ff e8 ff 71       lay     %r15,-24(%r15)
 232:   e3 e0 f0 98 00 24       stg     %r14,152(%r15)
 238:   c0 20 00 00 00 00       larl    %r2,238 
                        23a: R_390_PC32DBL      .LC48+0x2
 23e:   c0 e5 00 00 00 00       brasl   %r14,23e 
                        240: R_390_PLT32DBL     __warn_printk+0x2
 244:   af 00 00 00             mc      0,0
 248:   eb ef f0 a0 00 04       lmg     %r14,%r15,160(%r15)
 24e:   c0 f4 00 00 00 00       jg      24e 
                        250: R_390_PC32DBL      __s390_indirect_jump_r14+0x2

With this change the generated code looks like this:

0000000000000210 :
 210:   c0 04 00 00 00 00       jgnop   210 
 216:   ec 26 00 06 00 7c       cgijne  %r2,0,222 
 21c:   c0 f4 00 00 00 00       jg      21c 
                        21e: R_390_PC32DBL      __s390_indirect_jump_r14+0x2
 222:   c0 20 00 00 00 00       larl    %r2,222 
                        224: R_390_PC32DBL      __bug_table+0x2
 228:   c0 f4 00 00 00 00       jg      228 
                        22a: R_390_PLT32DBL     __WARN_trap+0x2

Downside is that the call trace now starts at __WARN_trap():

------------[ cut here ]------------
bar
WARNING: arch/s390/kernel/setup.c:1017 at 0x0, CPU#0: swapper/0/0
...
Krnl PSW : 0704c00180000000 000003ffe0f6a3b4 (__WARN_trap+0x4/0x10)
...
Krnl Code: 000003ffe0f6a3ac: 0707                bcr     0,%r7
           000003ffe0f6a3ae: 0707                bcr     0,%r7
          *000003ffe0f6a3b0: af000001            mc      1,0
          >000003ffe0f6a3b4: 07fe                bcr     15,%r14
           000003ffe0f6a3b6: 47000700            bc      0,1792
           000003ffe0f6a3ba: 0707                bcr     0,%r7
           000003ffe0f6a3bc: 0707                bcr     0,%r7
           000003ffe0f6a3be: 0707                bcr     0,%r7
Call Trace:
 [<000003ffe0f6a3b4>] __WARN_trap+0x4/0x10
([<000003ffe185a54c>] start_kernel+0x53c/0x5d8)
 [<000003ffe010002e>] startup_continue+0x2e/0x40

Which isn't too helpful. This can be addressed by just skipping __WARN_trap(),
which will be addressed in a later patch.

Reviewed-by: Sven Schnelle 
Signed-off-by: Heiko Carstens

s390/traps: Copy monitor code to pt_regs

2026-01-27T11:16:16+00:00

In case of a monitor call program check the CPU stores the monitor code to
lowcore. Let the program check handler copy it to the pt_regs structure so
it can be used by the monitor call exception handler.

Instead of increasing the pt_regs size add a union which contains both
orig_gpr2 and monitor_code, since orig_gpr2 is not used in case of a
program check.

Reviewed-by: Sven Schnelle 
Signed-off-by: Heiko Carstens

s390/bug: Introduce and use monitor code macro

2026-01-27T11:16:16+00:00

The first operand address of the monitor call (mc) instruction is the
monitor code. Currently the monitor code is ignored, but this will
change. Therefore add and use MONCODE_BUG instead of a hardcoded zero.

Reviewed-by: Sven Schnelle 
Signed-off-by: Heiko Carstens

Merge tag 's390-6.15-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

2025-03-29T18:59:43+00:00

Pull s390 updates from Vasily Gorbik:

 - Add sorting of mcount locations at build time

 - Rework uaccess functions with C exception handling to shorten inline
   assembly size and enable full inlining. This yields near-optimal code
   for small constant copies with a ~40kb kernel size increase

 - Add support for a configurable STRICT_MM_TYPECHECKS which allows to
   generate better code, but also allows to have type checking for debug
   builds

 - Optimize get_lowcore() for common callers with alternatives that
   nearly revert to the pre-relocated lowcore code, while also slightly
   reducing syscall entry and exit time

 - Convert MACHINE_HAS_* checks for single facility tests into cpu_has_*
   style macros that call test_facility(), and for features with
   additional conditions, add a new ALT_TYPE_FEATURE alternative to
   provide a static branch via alternative patching. Also, move machine
   feature detection to the decompressor for early patching and add
   debugging functionality to easily show which alternatives are patched

 - Add exception table support to early boot / startup code to get rid
   of the open coded exception handling

 - Use asm_inline for all inline assemblies with EX_TABLE or ALTERNATIVE
   to ensure correct inlining and unrolling decisions

 - Remove 2k page table leftovers now that s390 has been switched to
   always allocate 4k page tables

 - Split kfence pool into 4k mappings in arch_kfence_init_pool() and
   remove the architecture-specific kfence_split_mapping()

 - Use READ_ONCE_NOCHECK() in regs_get_kernel_stack_nth() to silence
   spurious KASAN warnings from opportunistic ftrace argument tracing

 - Force __atomic_add_const() variants on s390 to always return void,
   ensuring compile errors for improper usage

 - Remove s390's ioremap_wt() and pgprot_writethrough() due to
   mismatched semantics and lack of known users, relying on asm-generic
   fallbacks

 - Signal eventfd in vfio-ap to notify userspace when the guest AP
   configuration changes, including during mdev removal

 - Convert mdev_types from an array to a pointer in vfio-ccw and vfio-ap
   drivers to avoid fake flex array confusion

 - Cleanup trap code

 - Remove references to the outdated linux390@de.ibm.com address

 - Other various small fixes and improvements all over the code

* tag 's390-6.15-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux: (78 commits)
  s390: Use inline qualifier for all EX_TABLE and ALTERNATIVE inline assemblies
  s390/kfence: Split kfence pool into 4k mappings in arch_kfence_init_pool()
  s390/ptrace: Avoid KASAN false positives in regs_get_kernel_stack_nth()
  s390/boot: Ignore vmlinux.map
  s390/sysctl: Remove "vm/allocate_pgste" sysctl
  s390: Remove 2k vs 4k page table leftovers
  s390/tlb: Use mm_has_pgste() instead of mm_alloc_pgste()
  s390/lowcore: Use lghi instead llilh to clear register
  s390/syscall: Merge __do_syscall() and do_syscall()
  s390/spinlock: Implement SPINLOCK_LOCKVAL with inline assembly
  s390/smp: Implement raw_smp_processor_id() with inline assembly
  s390/current: Implement current with inline assembly
  s390/lowcore: Use inline qualifier for get_lowcore() inline assembly
  s390: Move s390 sysctls into their own file under arch/s390
  s390/syscall: Simplify syscall_get_arguments()
  s390/vfio-ap: Notify userspace that guest's AP config changed when mdev removed
  s390: Remove ioremap_wt() and pgprot_writethrough()
  s390/mm: Add configurable STRICT_MM_TYPECHECKS
  s390/mm: Convert pgste_val() into function
  s390/mm: Convert pgprot_val() into function
  ...

s390: Use inline qualifier for all EX_TABLE and ALTERNATIVE inline assemblies

2025-03-18T16:13:51+00:00

Use asm_inline for all inline assemblies which make use of the EX_TABLE or
ALTERNATIVE macros.

These macros expand to many lines and the compiler assumes the number of
lines within an inline assembly is the same as the number of instructions
within an inline assembly. This has an effect on inlining and loop
unrolling decisions.

In order to avoid incorrect assumptions use asm_inline, which tells the
compiler that an inline assembly has the smallest possible size.

In order to avoid confusion when asm_inline should be used or not, since a
couple of inline assemblies are quite large: the rule is to always use
asm_inline whenever the EX_TABLE or ALTERNATIVE macro is used. In specific
cases there may be reasons to not follow this guideline, but that should
be documented with the corresponding code.

Using the inline qualifier everywhere has only a small effect on the kernel
image size:

add/remove: 0/10 grow/shrink: 19/8 up/down: 1492/-1858 (-366)

The only location where this seems to matter is load_unaligned_zeropad()
from word-at-a-time.h where the compiler inlines more functions within the
dcache code, which is indeed code where performance matters.

Suggested-by: Juergen Christ 
Reviewed-by: Juergen Christ 
Signed-off-by: Heiko Carstens 
Signed-off-by: Vasily Gorbik

s390/traps: Change stack overflow message

2025-03-04T16:34:03+00:00

When the kernel stack pointer is pointing to invalid memory,
a 'Kernel stack overflow' message is printed, which is misleading.
Change the message to actually say that the stack pointer is invalid
instead.

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

s390/traps: Cleanup coding style

2025-03-04T16:34:03+00:00

Just some trivial whitespace and coding style changes.

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

s390/traps: Get rid of superfluous cpu_has_vx() check

2025-03-04T16:34:03+00:00

If the vector facility is installed cpu_has_vx() is always true, if it is
not installed the result is always false, and no vector exception can
happen. Therefore remove the superfluous check.

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

s390/traps: Use pr_emerg() instead of printk()

2025-03-04T16:34:03+00:00

Use pr_emerg() instead of printk() in case of a stack overflow,
providing the emergency printk level. Also slightly adjust the
printed text for pr_emerg() and panic().

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