membarrier-sync-core: Document architecture support

Web:        https://git.kernel.org/torvalds/c/6a546c7e69ff0b69581377cc70d7e8a601b98fce
Commit:     6a546c7e69ff0b69581377cc70d7e8a601b98fce
Parent:     f1517df8701c9f12dae9ce7f43a5d300a6917619
Refname:    refs/heads/master
Author:     Mathieu Desnoyers <[email protected]>
AuthorDate: Fri Feb 9 15:30:56 2018 -0500
Committer:  Ingo Molnar <[email protected]>
CommitDate: Sat Feb 10 12:45:10 2018 +0100

    membarrier-sync-core: Document architecture support
    
    Ensure we gather architecture requirements about each architecture
    supporting the "sync_core" membarrier command in a single file under
    Documentation/features.
    
    Signed-off-by: Mathieu Desnoyers <[email protected]>
    Cc: Andrea Parri <[email protected]>
    Cc: Andrew Hunter <[email protected]>
    Cc: Andy Lutomirski <[email protected]>
    Cc: Avi Kivity <[email protected]>
    Cc: Benjamin Herrenschmidt <[email protected]>
    Cc: Boqun Feng <[email protected]>
    Cc: Dave Watson <[email protected]>
    Cc: David Sehr <[email protected]>
    Cc: Greg Hackmann <[email protected]>
    Cc: Linus Torvalds <[email protected]>
    Cc: Maged Michael <[email protected]>
    Cc: Michael Ellerman <[email protected]>
    Cc: Paul E. McKenney <[email protected]>
    Cc: Paul Mackerras <[email protected]>
    Cc: Peter Zijlstra (Intel) <[email protected]>
    Cc: Peter Zijlstra <[email protected]>
    Cc: Russell King <[email protected]>
    Cc: Thomas Gleixner <[email protected]>
    Cc: Will Deacon <[email protected]>
    Cc: [email protected]
    Cc: [email protected]
    Link: http://lkml.kernel.org/r/[email protected]
    Signed-off-by: Ingo Molnar <[email protected]>
---
 .../sched/membarrier-sync-core/arch-support.txt    | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/Documentation/features/sched/membarrier-sync-core/arch-support.txt b/Documentation/features/sched/membarrier-sync-core/arch-support.txt
new file mode 100644
index 000000000000..2c815a7f1ba7
--- /dev/null
+++ b/Documentation/features/sched/membarrier-sync-core/arch-support.txt
@@ -0,0 +1,62 @@
+#
+# Feature name:          membarrier-sync-core
+#         Kconfig:       ARCH_HAS_MEMBARRIER_SYNC_CORE
+#         description:   arch supports core serializing membarrier
+#
+# Architecture requirements
+#
+# * arm64
+#
+# Rely on eret context synchronization 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: | TODO |
+    |       arm64: |  ok  |
+    |    blackfin: | TODO |
+    |         c6x: | TODO |
+    |        cris: | TODO |
+    |         frv: | TODO |
+    |       h8300: | TODO |
+    |     hexagon: | TODO |
+    |        ia64: | TODO |
+    |        m32r: | TODO |
+    |        m68k: | TODO |
+    |       metag: | TODO |
+    |  microblaze: | TODO |
+    |        mips: | TODO |
+    |     mn10300: | TODO |
+    |       nios2: | TODO |
+    |    openrisc: | TODO |
+    |      parisc: | TODO |
+    |     powerpc: | TODO |
+    |        s390: | TODO |
+    |       score: | TODO |
+    |          sh: | TODO |
+    |       sparc: | TODO |
+    |        tile: | TODO |
+    |          um: | TODO |
+    |   unicore32: | TODO |
+    |         x86: |  ok  |
+    |      xtensa: | TODO |
+    -----------------------
--
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