[PATCH v2 0/4] sparc64: kprobes: Make kprobes work on sun4v

[Stian Halseth <stian@itx.no>]

Any kprobe hit on a sun4v machine oopses. The probed instruction is
single-stepped from memory that is not executable there. Patch 1
moves the copy into an instruction slot from get_insn_slot(), as other
architectures do.

Once probes work, three older single-step bugs show up. A taken BPr or
FP branch resumes at the wrong address (patch 2). So does a probe on a
delay slot instruction (patch 3). An annulled branch can skip the
break instruction after the copy (patch 4). Patch 2 overlaps Danish
Khateeb's relbranch_fixup() fix from September. Whichever is applied
first, the other is a small rebase.

Tested on a SPARC T7-1 and T4-1 (sun4v) and a Sun Fire V240 (sun4u):
entry and return probes, probes on all 50 instructions of
__task_pid_nr_ns at once while checking getppid(), ps and /proc, probes
on the SPARC AES routines during AF_ALG encryption (sun4v), and
refusal of ba,a. Without the series the first probe hit oopses on
sun4v. A probe on a taken brnz oopses on sun4u as well.

v2: make flush_insn_slot() a no-op in patch 1 (Masami). The slot is
flushed in arch_prepare_kprobe() when it is written. A killed probe
has a NULL slot pointer. init_aggr_kprobe() flushed through it.
Patch 4 no longer touches the macro. Rebased onto 7.4-rc3. Build
tested on the T7-1.
v1: https://lore.kernel.org/all/20261009180336.1315684-1-stian@itx.no/

Stian Halseth (4):
  sparc64: kprobes: Single-step from an executable instruction slot
  sparc64: kprobes: Fix up register and FP branches after single-step
  sparc64: kprobes: Resume after a delay slot at the saved next PC
  sparc64: kprobes: Handle annulled branches

 arch/sparc/include/asm/kprobes.h | 14 +++----
 arch/sparc/kernel/kprobes.c      | 69 +++++++++++++++++++++++++++-----
 2 files changed, 66 insertions(+), 17 deletions(-)


base-commit: b3dfbde62cf1981c4638939c159dfd087b7a72e9
-- 
2.43.0