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Message-ID: <8132d732-b9e8-4a52-be5d-74db7a159136@efficios.com>
Date: Mon, 11 Dec 2023 08:34:21 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Andrea Parri <parri.andrea@...il.com>, paulmck@...nel.org,
palmer@...belt.com, paul.walmsley@...ive.com, aou@...s.berkeley.edu
Cc: mmaas@...gle.com, hboehm@...gle.com, striker@...ibm.com,
charlie@...osinc.com, rehn@...osinc.com,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 4/4] membarrier: Introduce Kconfig ARCH_HAS_MEMBARRIER
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@...icios.com>
> Signed-off-by: Andrea Parri <parri.andrea@...il.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@...icios.com>
> M: "Paul E. McKenney" <paulmck@...nel.org>
> L: linux-kernel@...r.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);
> }
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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