CVS commit: src/sys/arch

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

Module Name:    src
Committed By:   riastradh
Date:           Sun Nov 14 16:56:32 UTC 2021

Modified Files:
        src/sys/arch/aarch64/aarch64: locore.S
        src/sys/arch/arm/arm: armv6_start.S cpu_subr.c

Log Message:
arm: Fix CPU startup synchronization.

- Use load-acquire instead of (wrong) membar_consumer then load in
  cpu_boot_secondary_processors and cpu_hatched_p.

  => (Could use load then membar_consumer instead but load-acquire is
     shorter.)

- Issue  dmb ish  before setting or clearing the bit in
  cpu_set_hatched and cpu_clr_mbox to effect a store-release.

  => (Could use membar_exit, which is semantically weaker than  dmb ish
     but on arm is just implemented as  dmb ish.)

  => (Could use stlr except we don't have atomic_ops(9) to do that.)

This way, everything before cpu_set_hatched or cpu_clr_mbox is
guaranteed to happen before everything after
cpu_boot_secondary_processors, which was previously not guaranteed.


To generate a diff of this commit:
cvs rdiff -u -r1.82 -r1.83 src/sys/arch/aarch64/aarch64/locore.S
cvs rdiff -u -r1.36 -r1.37 src/sys/arch/arm/arm/armv6_start.S
cvs rdiff -u -r1.4 -r1.5 src/sys/arch/arm/arm/cpu_subr.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.