linux-kernel - [RFC PATCH] membarrier-sync-core: Document architecture support

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Message-Id: <1517936413-19675-1-git-send-email-mathieu.desnoyers@efficios.com>
Date:   Tue,  6 Feb 2018 12:00:13 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Andrew Hunter <ahh@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Avi Kivity <avi@...lladb.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Dave Watson <davejwatson@...com>, David Sehr <sehr@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Maged Michael <maged.michael@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: [RFC PATCH] 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.

[ This patch applies on top of tip sched/core. ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Andrea Parri <parri.andrea@...il.com>
Cc: Andrew Hunter <ahh@...gle.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Avi Kivity <avi@...lladb.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Dave Watson <davejwatson@...com>
Cc: David Sehr <sehr@...gle.com>
Cc: Greg Hackmann <ghackmann@...gle.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Maged Michael <maged.michael@...il.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: Will Deacon <will.deacon@....com>
Cc: linux-api@...r.kernel.org
Cc: linux-arch@...r.kernel.org
---
 .../sched/membarrier-sync-core/arch-support.txt    | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 Documentation/features/sched/membarrier-sync-core/arch-support.txt

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 0000000..2c815a7
--- /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 |
+    -----------------------
-- 
1.9.1