[PATCH v2 0/4] ARM: allocate the cacheinfo early to fix the PREEMPT_RT boot warning

[Karl Mehltretter]

This series moves ARM cacheinfo allocation to the boot CPU to avoid
sleeping-lock warnings during PREEMPT_RT secondary-CPU startup. It is
rebased onto v7.3-rc1, cee9395acd8043be0644b25c34bfa86623f2b935.

Patches 1-3 prepare for early allocation: bound cache-leaf writes,
include external caches in the allocation size, and guard CLIDR reads
on older CPUs. Patch 4 enables early allocation. Please take all four
patches together for stable.

Changes in v2:
- Rebase from post-v7.3-rc2 mainline (5225b8eec4c9) onto v7.3-rc1
  as Linus requested [1].
- Add Sebastian's Tested-by and links to the original patch posts.
- Retest the full series on this base; results below.
The four code diffs are unchanged.

Fresh testing on this v7.3-rc1 base used GCC 15.2.0 and QEMU 10.2.1.
Three full kernel builds and W=1 checks of cacheinfo.o/topology.o passed:
multi_v7_defconfig with and without PREEMPT_RT, and an ARMv6+ARMv7 SMP
PREEMPT_RT configuration for ARM11 MPCore. Seven boot checks passed:
- virt, Cortex-A15, 2 and 4 CPUs, with and without PREEMPT_RT;
- vexpress-a9, Cortex-A9 with external PL310 L2, 4 CPUs, RT and non-RT;
- realview-eb-mpcore, ARM11 MPCore, 4 CPUs, PREEMPT_RT.

With DEBUG_ATOMIC_SLEEP enabled, the RT boot warning was absent.
CPU1 offline/online succeeded in every run, with identical cache sysfs
output before and after. ARM11 exposed no cache leaves, as expected.
RT and non-RT cache output also matched on each ARMv7 machine.
All four stable patch IDs match v1.

Earlier testing of these same diffs also covered DT cache-description
corner cases. On September 12, the full series passed on a Raspberry
Pi 400 with a 32-bit PREEMPT_RT 7.2.6-rc1 kernel: the boot warning was
absent and all 12 cache sysfs entries matched the baseline. CPU hotplug
was unavailable there. That hardware test and the DT corner-case tests
were not repeated on this rebased tree.

v1: https://lore.kernel.org/r/20260912195552.76673-1-kmehltretter@xxxxxxxxx/
[1] https://lore.kernel.org/r/CAD++jL=7OSrPMax9GRj3D7ehjmmG2uMyws53F8U0x7YGx+RNOQ@xxxxxxxxxxxxxx/

Karl Mehltretter (4):
  ARM: cacheinfo: avoid out-of-bounds write in populate_cache_leaves()
  ARM: cacheinfo: count external caches in early_cache_level()
  ARM: cacheinfo: guard the CLIDR read in populate_cache_leaves()
  ARM: topology: allocate the cacheinfo early on the boot CPU

 arch/arm/kernel/cacheinfo.c | 49 +++++++++++++++++++++++----------------------
 arch/arm/kernel/topology.c  | 13 ++++++++++++
 2 files changed, 38 insertions(+), 24 deletions(-)

base-commit: cee9395acd8043be0644b25c34bfa86623f2b935