s390: enable ARCH_HAS_MEMBARRIER_SYNC_CORE

[linux-2.6-block.git] / Documentation / features / sched / membarrier-sync-core / arch-support.txt

#
# Feature name:          membarrier-sync-core
#         Kconfig:       ARCH_HAS_MEMBARRIER_SYNC_CORE
#         description:   arch supports core serializing membarrier
#
# Architecture requirements
#
# * arm/arm64/powerpc/s390
#
# Rely on implicit context synchronization as a result of exception return
# when returning from IPI handler, and when returning to user-space.
#
# * x86
#
# x86-32 uses IRET as return from interrupt, which takes care of the IPI.
# However, it uses both IRET and SYSEXIT to go back to user-space. The IRET
# instruction is core serializing, but not SYSEXIT.
#
# x86-64 uses IRET as return from interrupt, which takes care of the IPI.
# However, it can return to user-space through either SYSRETL (compat code),
# SYSRETQ, or IRET.
#
# Given that neither SYSRET{L,Q}, nor SYSEXIT, are core serializing, we rely
# instead on write_cr3() performed by switch_mm() to provide core serialization
# after changing the current mm, and deal with the special case of kthread ->
# uthread (temporarily keeping current mm into active_mm) by issuing a
# sync_core_before_usermode() in that specific case.
#
    -----------------------
    |         arch |status|
    -----------------------
    |       alpha: | TODO |
    |         arc: | TODO |
    |         arm: |  ok  |
    |       arm64: |  ok  |
    |        csky: | TODO |
    |     hexagon: | TODO |
    |        ia64: | TODO |
    |   loongarch: | TODO |
    |        m68k: | TODO |
    |  microblaze: | TODO |
    |        mips: | TODO |
    |       nios2: | TODO |
    |    openrisc: | TODO |
    |      parisc: | TODO |
    |     powerpc: |  ok  |
    |       riscv: | TODO |
    |        s390: |  ok  |
    |          sh: | TODO |
    |       sparc: | TODO |
    |          um: | TODO |
    |         x86: |  ok  |
    |      xtensa: | TODO |
    -----------------------