From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-lf1-f44.google.com (mail-lf1-f44.google.com [209.85.167.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7ABBD4CB5E; Wed, 10 Jan 2024 14:56:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Y9ktPFDY" Received: by mail-lf1-f44.google.com with SMTP id 2adb3069b0e04-50e80d40a41so5297519e87.1; Wed, 10 Jan 2024 06:56:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1704898571; x=1705503371; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=rLaTiUEqnhHpEDzcjzh0LRpXh9TZeJ5JQ1BIVLM+gqw=; b=Y9ktPFDYCVz/ffcN52D0ChirQmJnD4Do8vsa0FpcHpPLUJvipD3indQIjC2PNGbBgA QlSJPa2T9YCK+pwHPuA/oa9czSP2BDw1PCOG7tMMPLdy00QZ3CF0lW4z5MmKEOx8SY6S t7h1R4RWaLA34eDfCfTSz67wQ8Pj1lNNVseQPTn87A0yoNomNaVRbKR3QPyu3irtI/Rz 1fojrnrRbrRlDru4t7e94YNa3It5bZ+pc+iYZAxqQznOK375XYdhMnX9N5kD0P+nRBgI pDKe105a+b5yqAQ8V06a+E0Kh927aWTRlnRC3g+9wBEyvVudVrAM7Ip593opUmGYVs8+ Dsyg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704898571; x=1705503371; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=rLaTiUEqnhHpEDzcjzh0LRpXh9TZeJ5JQ1BIVLM+gqw=; b=GdaE7o6qy0pNdXjAppZ5WicFbghUxG9xVlwyXwSqzywWrbBnCxivGE7VGTWngoipmh lZWFI9NeEaORgay6f8F5QrLwMCKVblhhzCvRdYdDvOlEe78hiz7s6Ru2W99UR3A7zbNg T4eZP568+zhbGa2E0xbEcODPXrNmqFlvfn7ymnmYBm31qKbzVuv8oDaL+TusV7OHMygW h3gPO/UrtdCYnsQjyTingyZupFs0ohg+7MrqnGr+EOCzVYvY/TPuEXu6qPR883BNIXMz cIvoI4K5cvhUIEbySvsi7H+u7/w6G3aOkNsf7omXyM0mM9TQKMWMxqce0qIDPF75ZLVi ogtQ== X-Gm-Message-State: AOJu0YyGX7jUZkNFr8JgiXmVhiUT/gtxqHR9H/CPwPJ6DttA++0J4sGS HzeUDleAEWMIHTbZ19GgO08= X-Google-Smtp-Source: AGHT+IEmWsRJPIzVvjKSG3W4CxovtYvIz/tPv4lvUtVx2c7SaE5vrwQD+TOsnx1Ylj+gfn5QPpRuDQ== X-Received: by 2002:ac2:51b7:0:b0:50e:9343:64df with SMTP id f23-20020ac251b7000000b0050e934364dfmr488193lfk.70.1704898571178; Wed, 10 Jan 2024 06:56:11 -0800 (PST) Received: from andrea.wind3.hub ([31.189.29.12]) by smtp.gmail.com with ESMTPSA id bm3-20020a170906c04300b00a2a4efe7d3dsm2161032ejb.79.2024.01.10.06.56.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jan 2024 06:56:10 -0800 (PST) From: Andrea Parri To: paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, mathieu.desnoyers@efficios.com, paulmck@kernel.org, corbet@lwn.net Cc: mmaas@google.com, hboehm@google.com, striker@us.ibm.com, charlie@rivosinc.com, rehn@rivosinc.com, linux-riscv@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Andrea Parri Subject: [PATCH v3 4/4] membarrier: riscv: Provide core serializing command Date: Wed, 10 Jan 2024 15:55:33 +0100 Message-Id: <20240110145533.60234-5-parri.andrea@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240110145533.60234-1-parri.andrea@gmail.com> References: <20240110145533.60234-1-parri.andrea@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit RISC-V uses xRET instructions on return from interrupt and to go back to user-space; the xRET instruction is not core serializing. Use FENCE.I for providing core serialization as follows: - by calling sync_core_before_usermode() on return from interrupt (cf. ipi_sync_core()), - via switch_mm() and sync_core_before_usermode() (respectively, for uthread->uthread and kthread->uthread transitions) to go back to user-space. On RISC-V, the serialization in switch_mm() is activated by resetting the icache_stale_mask of the mm at prepare_sync_core_cmd(). Suggested-by: Palmer Dabbelt Signed-off-by: Andrea Parri --- .../membarrier-sync-core/arch-support.txt | 18 +++++++++++- MAINTAINERS | 1 + arch/riscv/Kconfig | 3 ++ arch/riscv/include/asm/membarrier.h | 19 ++++++++++++ arch/riscv/include/asm/sync_core.h | 29 +++++++++++++++++++ kernel/sched/core.c | 4 +++ kernel/sched/membarrier.c | 4 +++ 7 files changed, 77 insertions(+), 1 deletion(-) create mode 100644 arch/riscv/include/asm/sync_core.h diff --git a/Documentation/features/sched/membarrier-sync-core/arch-support.txt b/Documentation/features/sched/membarrier-sync-core/arch-support.txt index d96b778b87ed8..a163170fc0f48 100644 --- a/Documentation/features/sched/membarrier-sync-core/arch-support.txt +++ b/Documentation/features/sched/membarrier-sync-core/arch-support.txt @@ -10,6 +10,22 @@ # Rely on implicit context synchronization as a result of exception return # when returning from IPI handler, and when returning to user-space. # +# * riscv +# +# riscv uses xRET as return from interrupt and to return to user-space. +# +# Given that xRET is not core serializing, we rely on FENCE.I for providing +# core serialization: +# +# - by calling sync_core_before_usermode() on return from interrupt (cf. +# ipi_sync_core()), +# +# - via switch_mm() and sync_core_before_usermode() (respectively, for +# uthread->uthread and kthread->uthread transitions) to go back to +# user-space. +# +# The serialization in switch_mm() is activated by prepare_sync_core_cmd(). +# # * x86 # # x86-32 uses IRET as return from interrupt, which takes care of the IPI. @@ -43,7 +59,7 @@ | openrisc: | TODO | | parisc: | TODO | | powerpc: | ok | - | riscv: | TODO | + | riscv: | ok | | s390: | ok | | sh: | TODO | | sparc: | TODO | diff --git a/MAINTAINERS b/MAINTAINERS index 6bce0aeecb4f2..e4ca6288ea3d1 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -13817,6 +13817,7 @@ L: linux-kernel@vger.kernel.org S: Supported F: Documentation/scheduler/membarrier.rst F: arch/*/include/asm/membarrier.h +F: arch/*/include/asm/sync_core.h F: include/uapi/linux/membarrier.h F: kernel/sched/membarrier.c diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 33d9ea5fa392f..2ad63a216d69a 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -28,14 +28,17 @@ config RISCV select ARCH_HAS_GIGANTIC_PAGE select ARCH_HAS_KCOV select ARCH_HAS_MEMBARRIER_CALLBACKS + select ARCH_HAS_MEMBARRIER_SYNC_CORE select ARCH_HAS_MMIOWB select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE select ARCH_HAS_PMEM_API + select ARCH_HAS_PREPARE_SYNC_CORE_CMD select ARCH_HAS_PTE_SPECIAL select ARCH_HAS_SET_DIRECT_MAP if MMU select ARCH_HAS_SET_MEMORY if MMU select ARCH_HAS_STRICT_KERNEL_RWX if MMU && !XIP_KERNEL select ARCH_HAS_STRICT_MODULE_RWX if MMU && !XIP_KERNEL + select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE select ARCH_HAS_SYSCALL_WRAPPER select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST select ARCH_HAS_UBSAN_SANITIZE_ALL diff --git a/arch/riscv/include/asm/membarrier.h b/arch/riscv/include/asm/membarrier.h index 6c016ebb5020a..47b240d0d596a 100644 --- a/arch/riscv/include/asm/membarrier.h +++ b/arch/riscv/include/asm/membarrier.h @@ -22,6 +22,25 @@ static inline void membarrier_arch_switch_mm(struct mm_struct *prev, /* * The membarrier system call requires a full memory barrier * after storing to rq->curr, before going back to user-space. + * + * This barrier is also needed for the SYNC_CORE command when + * switching between processes; in particular, on a transition + * from a thread belonging to another mm to a thread belonging + * to the mm for which a membarrier SYNC_CORE is done on CPU0: + * + * - [CPU0] sets all bits in the mm icache_stale_mask (in + * prepare_sync_core_cmd()); + * + * - [CPU1] stores to rq->curr (by the scheduler); + * + * - [CPU0] loads rq->curr within membarrier and observes + * cpu_rq(1)->curr->mm != mm, so the IPI is skipped on + * CPU1; this means membarrier relies on switch_mm() to + * issue the sync-core; + * + * - [CPU1] switch_mm() loads icache_stale_mask; if the bit + * is zero, switch_mm() may incorrectly skip the sync-core. + * * Matches a full barrier in the proximity of the membarrier * system call entry. */ diff --git a/arch/riscv/include/asm/sync_core.h b/arch/riscv/include/asm/sync_core.h new file mode 100644 index 0000000000000..9153016da8f14 --- /dev/null +++ b/arch/riscv/include/asm/sync_core.h @@ -0,0 +1,29 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_RISCV_SYNC_CORE_H +#define _ASM_RISCV_SYNC_CORE_H + +/* + * RISC-V implements return to user-space through an xRET instruction, + * which is not core serializing. + */ +static inline void sync_core_before_usermode(void) +{ + asm volatile ("fence.i" ::: "memory"); +} + +#ifdef CONFIG_SMP +/* + * Ensure the next switch_mm() on every CPU issues a core serializing + * instruction for the given @mm. + */ +static inline void prepare_sync_core_cmd(struct mm_struct *mm) +{ + cpumask_setall(&mm->context.icache_stale_mask); +} +#else +static inline void prepare_sync_core_cmd(struct mm_struct *mm) +{ +} +#endif /* CONFIG_SMP */ + +#endif /* _ASM_RISCV_SYNC_CORE_H */ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index b51bc86f8340c..82de2b7d253cd 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6682,6 +6682,10 @@ static void __sched notrace __schedule(unsigned int sched_mode) * * The barrier matches a full barrier in the proximity of * the membarrier system call entry. + * + * On RISC-V, this barrier pairing is also needed for the + * SYNC_CORE command when switching between processes, cf. + * the inline comments in membarrier_arch_switch_mm(). */ ++*switch_count; diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index 6d1f31b3a967b..703e8d80a576d 100644 --- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -342,6 +342,10 @@ static int membarrier_private_expedited(int flags, int cpu_id) /* * Matches memory barriers after rq->curr modification in * scheduler. + * + * On RISC-V, this barrier pairing is also needed for the + * SYNC_CORE command when switching between processes, cf. + * the inline comments in membarrier_arch_switch_mm(). */ smp_mb(); /* system call entry is not a mb. */ -- 2.34.1