Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:4 as permitted sender) client-ip=2620:137:e000::3:4;
From:   Andrea Parri <parri.andrea@gmail.com>
To:     mathieu.desnoyers@efficios.com, paulmck@kernel.org,
        palmer@dabbelt.com, paul.walmsley@sifive.com, aou@eecs.berkeley.edu
Cc:     mmaas@google.com, hboehm@google.com, striker@us.ibm.com,
        charlie@rivosinc.com, rehn@rivosinc.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        Andrea Parri <parri.andrea@gmail.com>
Subject: [RFC PATCH 4/4] membarrier: Introduce Kconfig ARCH_HAS_MEMBARRIER
Date:   Mon, 11 Dec 2023 10:44:14 +0100
Message-Id: <20231211094414.8078-5-parri.andrea@gmail.com>
In-Reply-To: <20231211094414.8078-1-parri.andrea@gmail.com>
References: <20231211094414.8078-1-parri.andrea@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Architectures supporting the "private expedited" membarrier command must
select the Kconfig to use the command.  Document status and requirements
for each architecture in a single file under Documentation/features.

Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
The TODOs in the arch-support table below should really be interpreted
as "I'm not sure/haven't checked" (the respective arch maintainers will
be able to verify and amend such information).

Based on the following inline comment in __schedule():

	/*
	 * The membarrier system call requires each architecture
	 * to have a full memory barrier after updating
	 * rq->curr, before returning to user-space.
	 *
	 * Here are the schemes providing that barrier on the
	 * various architectures:
	 * - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC,
	 *   RISC-V.  switch_mm() relies on membarrier_arch_switch_mm()
	 *   on PowerPC and on RISC-V.
	 * - finish_lock_switch() for weakly-ordered
	 *   architectures where spin_unlock is a full barrier,
	 * - switch_to() for arm64 (weakly-ordered, spin_unlock
	 *   is a RELEASE barrier),
	 */

 .../sched/membarrier/arch-support.txt         | 50 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 arch/alpha/Kconfig                            |  1 +
 arch/arc/Kconfig                              |  1 +
 arch/arm/Kconfig                              |  1 +
 arch/arm64/Kconfig                            |  1 +
 arch/hexagon/Kconfig                          |  1 +
 arch/mips/Kconfig                             |  1 +
 arch/powerpc/Kconfig                          |  1 +
 arch/riscv/Kconfig                            |  1 +
 arch/s390/Kconfig                             |  1 +
 arch/sparc/Kconfig                            |  1 +
 arch/x86/Kconfig                              |  1 +
 init/Kconfig                                  |  3 ++
 kernel/sched/core.c                           |  4 +-
 kernel/sched/membarrier.c                     | 15 +++++-
 16 files changed, 80 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/features/sched/membarrier/arch-support.txt

diff --git a/Documentation/features/sched/membarrier/arch-support.txt b/Documentation/features/sched/membarrier/arch-support.txt
new file mode 100644
index 0000000000000..95e65195e47c2
--- /dev/null
+++ b/Documentation/features/sched/membarrier/arch-support.txt
@@ -0,0 +1,50 @@
+#
+# Feature name:          membarrier
+#         Kconfig:       ARCH_HAS_MEMBARRIER
+#         description:   arch supports MEMBARRIER_CMD_PRIVATE_EXPEDITED
+#
+# Architecture requirements
+#
+# The membarrier() system call requires each architecture to have a full memory
+# barrier after updating rq->curr, before returning to user-space.
+#
+# Here are the schemes providing that barrier on the various architectures:
+#
+# * alpha/arc/arm/hexagon/mips
+#
+# We rely on the full barrier implied by spin_unlock() in finish_lock_switch().
+#
+# * arm64
+#
+# We rely on the full barrier implied by switch_to().
+#
+# * powerpc/riscv/s390/sparc/x86
+#
+# We rely on the full barrier implied by switch_mm(), if mm isn't NULL; we rely
+# on the full barrier implied by mmdrop(), otherwise.
+#
+    -----------------------
+    |         arch |status|
+    -----------------------
+    |       alpha: |  ok  |
+    |         arc: |  ok  |
+    |         arm: |  ok  |
+    |       arm64: |  ok  |
+    |        csky: | TODO |
+    |     hexagon: |  ok  |
+    |   loongarch: | TODO |
+    |        m68k: | TODO |
+    |  microblaze: | TODO |
+    |        mips: |  ok  |
+    |       nios2: | TODO |
+    |    openrisc: | TODO |
+    |      parisc: | TODO |
+    |     powerpc: |  ok  |
+    |       riscv: |  ok  |
+    |        s390: |  ok  |
+    |          sh: | TODO |
+    |       sparc: |  ok  |
+    |          um: | TODO |
+    |         x86: |  ok  |
+    |      xtensa: | TODO |
+    -----------------------
diff --git a/MAINTAINERS b/MAINTAINERS
index f6f1fdc76cf46..c5a053605cbc4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13807,6 +13807,7 @@ M:	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 M:	"Paul E. McKenney" <paulmck@kernel.org>
 L:	linux-kernel@vger.kernel.org
 S:	Supported
+F:	Documentation/features/sched/membarrier*/
 F:	arch/*/include/asm/membarrier.h
 F:	arch/*/include/asm/sync_core.h
 F:	include/uapi/linux/membarrier.h
diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index d6968d090d49a..f98d6cba0bd9a 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -24,6 +24,7 @@ config ALPHA
 	select GENERIC_IRQ_SHOW
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select ARCH_HAVE_NMI_SAFE_CMPXCHG
+	select ARCH_HAS_MEMBARRIER
 	select AUDIT_ARCH
 	select GENERIC_CPU_VULNERABILITIES
 	select GENERIC_SMP_IDLE_THREAD
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 3162db540ee96..1d8a6ba98ae33 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -9,6 +9,7 @@ config ARC
 	select ARCH_HAS_CACHE_LINE_SIZE
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DMA_PREP_COHERENT
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SETUP_DMA_OPS
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f8567e95f98be..700d1d9ff2f8b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -14,6 +14,7 @@ config ARM
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_KEEPINITRD
 	select ARCH_HAS_KCOV
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
 	select ARCH_HAS_PTE_SPECIAL if ARM_LPAE
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7b071a00425d2..d21788e6920f6 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -31,6 +31,7 @@ config ARM64
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_KEEPINITRD
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
diff --git a/arch/hexagon/Kconfig b/arch/hexagon/Kconfig
index a880ee067d2ec..c2b2713c01bbd 100644
--- a/arch/hexagon/Kconfig
+++ b/arch/hexagon/Kconfig
@@ -5,6 +5,7 @@ comment "Linux Kernel Configuration for Hexagon"
 config HEXAGON
 	def_bool y
 	select ARCH_32BIT_OFF_T
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select ARCH_NO_PREEMPT
 	select DMA_GLOBAL_POOL
diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 797ae590ebdba..4b65e73e34c16 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -16,6 +16,7 @@ config MIPS
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARCH_HAS_GCOV_PROFILE_ALL
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_KEEP_MEMBLOCK
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 6f105ee4f3cf5..c13980eac3585 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -137,6 +137,7 @@ config PPC
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_HUGEPD			if HUGETLB_PAGE
 	select ARCH_HAS_KCOV
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_MEMBARRIER_CALLBACKS
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_MEMREMAP_COMPAT_ALIGN	if PPC_64S_HASH_MMU
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index db7b1acd943e4..fd4c6a74ebd61 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -27,6 +27,7 @@ config RISCV
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_MEMBARRIER_CALLBACKS
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_MMIOWB
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 3bec98d20283b..2e044d424fd4a 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -72,6 +72,7 @@ config S390
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_HAS_KCOV
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_MEM_ENCRYPT
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 49849790e66dc..40eb179c2416a 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -30,6 +30,7 @@ config SPARC
 	select RTC_SYSTOHC
 	select HAVE_ARCH_JUMP_LABEL if SPARC64
 	select GENERIC_IRQ_SHOW
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select GENERIC_PCI_IOMAP
 	select HAS_IOPORT
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 3762f41bb0929..83f63e00312ee 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -82,6 +82,7 @@ config X86
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_KCOV			if X86_64
 	select ARCH_HAS_MEM_ENCRYPT
+	select ARCH_HAS_MEMBARRIER
 	select ARCH_HAS_MEMBARRIER_SYNC_CORE
 	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
diff --git a/init/Kconfig b/init/Kconfig
index 87daf50838f02..8114404b52b91 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1742,6 +1742,9 @@ config KALLSYMS_BASE_RELATIVE
 
 # syscall, maps, verifier
 
+config ARCH_HAS_MEMBARRIER
+	bool
+
 config ARCH_HAS_MEMBARRIER_CALLBACKS
 	bool
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 711dc753f7216..dff1c6df337f9 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6673,8 +6673,8 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 		 * - mm ? switch_mm() : mmdrop() for x86, s390, sparc, PowerPC,
 		 *   RISC-V.  switch_mm() relies on membarrier_arch_switch_mm()
 		 *   on PowerPC and on RISC-V.
-		 * - finish_lock_switch() for weakly-ordered
-		 *   architectures where spin_unlock is a full barrier,
+		 * - finish_lock_switch() for alpha, arc, arm, hexagon, mips
+		 *   where spin_unlock is a full barrier,
 		 * - switch_to() for arm64 (weakly-ordered, spin_unlock
 		 *   is a RELEASE barrier),
 		 */
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 58f801e013988..248a38c9b261c 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -137,6 +137,14 @@
  * Bitmask made from a "or" of all commands within enum membarrier_cmd,
  * except MEMBARRIER_CMD_QUERY.
  */
+#ifdef CONFIG_ARCH_HAS_MEMBARRIER
+#define MEMBARRIER_PRIVATE_EXPEDITED_BITMASK			\
+	(MEMBARRIER_CMD_PRIVATE_EXPEDITED			\
+	| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED)
+#else
+#define MEMBARRIER_PRIVATE_EXPEDITED_BITMASK	0
+#endif
+
 #ifdef CONFIG_ARCH_HAS_MEMBARRIER_SYNC_CORE
 #define MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK			\
 	(MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE			\
@@ -156,8 +164,7 @@
 #define MEMBARRIER_CMD_BITMASK						\
 	(MEMBARRIER_CMD_GLOBAL | MEMBARRIER_CMD_GLOBAL_EXPEDITED	\
 	| MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED			\
-	| MEMBARRIER_CMD_PRIVATE_EXPEDITED				\
-	| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED			\
+	| MEMBARRIER_PRIVATE_EXPEDITED_BITMASK				\
 	| MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK		\
 	| MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK			\
 	| MEMBARRIER_CMD_GET_REGISTRATIONS)
@@ -329,6 +336,8 @@ static int membarrier_private_expedited(int flags, int cpu_id)
 			return -EPERM;
 		ipi_func = ipi_rseq;
 	} else {
+		if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER))
+			return -EINVAL;
 		WARN_ON_ONCE(flags);
 		if (!(atomic_read(&mm->membarrier_state) &
 		      MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY))
@@ -519,6 +528,8 @@ static int membarrier_register_private_expedited(int flags)
 		ready_state =
 			MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY;
 	} else {
+		if (!IS_ENABLED(CONFIG_ARCH_HAS_MEMBARRIER))
+			return -EINVAL;
 		WARN_ON_ONCE(flags);
 	}
 
-- 
2.34.1