1# 2# Feature name: membarrier-sync-core 3# Kconfig: ARCH_HAS_MEMBARRIER_SYNC_CORE 4# description: arch supports core serializing membarrier 5# 6# Architecture requirements 7# 8# * arm/arm64/powerpc/s390 9# 10# Rely on implicit context synchronization as a result of exception return 11# when returning from IPI handler, and when returning to user-space. 12# 13# * riscv 14# 15# riscv uses xRET as return from interrupt and to return to user-space. 16# 17# Given that xRET is not core serializing, we rely on FENCE.I for providing 18# core serialization: 19# 20# - by calling sync_core_before_usermode() on return from interrupt (cf. 21# ipi_sync_core()), 22# 23# - via switch_mm() and sync_core_before_usermode() (respectively, for 24# uthread->uthread and kthread->uthread transitions) before returning 25# to user-space. 26# 27# The serialization in switch_mm() is activated by prepare_sync_core_cmd(). 28# 29# * x86 30# 31# x86-32 uses IRET as return from interrupt, which takes care of the IPI. 32# However, it uses both IRET and SYSEXIT to go back to user-space. The IRET 33# instruction is core serializing, but not SYSEXIT. 34# 35# x86-64 uses IRET as return from interrupt, which takes care of the IPI. 36# However, it can return to user-space through either SYSRETL (compat code), 37# SYSRETQ, or IRET. 38# 39# Given that neither SYSRET{L,Q}, nor SYSEXIT, are core serializing, we rely 40# instead on write_cr3() performed by switch_mm() to provide core serialization 41# after changing the current mm, and deal with the special case of kthread -> 42# uthread (temporarily keeping current mm into active_mm) by issuing a 43# sync_core_before_usermode() in that specific case. 44# 45 ----------------------- 46 | arch |status| 47 ----------------------- 48 | alpha: | TODO | 49 | arc: | TODO | 50 | arm: | ok | 51 | arm64: | ok | 52 | csky: | TODO | 53 | hexagon: | TODO | 54 | loongarch: | TODO | 55 | m68k: | TODO | 56 | microblaze: | TODO | 57 | mips: | TODO | 58 | nios2: | TODO | 59 | openrisc: | TODO | 60 | parisc: | TODO | 61 | powerpc: | ok | 62 | riscv: | ok | 63 | s390: | ok | 64 | sh: | TODO | 65 | sparc: | TODO | 66 | um: | TODO | 67 | x86: | ok | 68 | xtensa: | TODO | 69 ----------------------- 70