Re: [RFC PATCH 4/4] membarrier: Introduce Kconfig ARCH_HAS_MEMBARRIER

From: Mathieu Desnoyers
Date: Mon Dec 11 2023 - 08:34:27 EST

On 2023-12-11 04:44, Andrea Parri wrote:
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.

Sorry for being vague in my suggestion: I did not intend to make it
optional (not ARCH_HAS_MEMBARRIER), but rather just to have a central
place where this would be documented.

I'm not sure where in Documentation this should land though ?

Thanks,

Mathieu



Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx>
---
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@xxxxxxxxxxxx>
M: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
L: linux-kernel@xxxxxxxxxxxxxxx
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);
}

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com