From patchwork Mon Jan 8 06:21:45 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 13513018 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C1CCCC3DA6E for ; Mon, 8 Jan 2024 06:22:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:In-Reply-To:References:Message-Id :MIME-Version:Subject:Date:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=jlj1Tw1HArK3UTH6JZUbeSX9h/7z55MKCYseiHEzHps=; b=np3GsOK/l+fUgz xq/P3c44TEPP0g0HpwppWvJ8JmFd842ucIk9uI7wcqgF9cIcZz3kK0foBdLRR2/FTTzcvolidlL8H IFvqi2RMb4gb9hzAD5/xYZlpB+yabfnHEK7oIMN5pngh9gNhCXWlNr9PDHBJzzlc9/G2RRRNBa8cz MUfEEovgd9jMk8wbFC48jFo9vy7KV8GBFYAq9y3Fd3NrfQhWnpTQSBwZKtHfGXu+IPoE2AsNNNxxb BKkMKZXhtYA6UkLxZBmbsSVF4UmFhHDRG91fd0+3bpjHfzlRD93T9BYUt0ktcDpLaT7ipgOoqFioJ MJ7pPRK9JTgachp09Exg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rMj1L-0043cE-2p; Mon, 08 Jan 2024 06:21:59 +0000 Received: from mail-oo1-xc2f.google.com ([2607:f8b0:4864:20::c2f]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rMj1F-0043Ya-0w for linux-riscv@lists.infradead.org; Mon, 08 Jan 2024 06:21:56 +0000 Received: by mail-oo1-xc2f.google.com with SMTP id 006d021491bc7-59612e4a21eso225318eaf.3 for ; Sun, 07 Jan 2024 22:21:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1704694911; x=1705299711; darn=lists.infradead.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=rTagxW2qGB+SOLygMjXPo1Qtb5o4FGjhXHBVBibN0pU=; b=T5EKhOg0XcvFXj/+VDlhtNOt0bf23oUnDWpc8Z5xe5fqa62NMM2p4IOheEEJaQgFlm 9U+yzggLa76LT9flpbafscbysQbmKOby4IQwBWX/zd7uw3KHpbesNQCdKEbi9VO3bvaT OV623TP5AoLmhIoNTiPh7NBiG5ctJVRoAfgnM31TIXEZdwsQGLfW5LxyETJ6C3dm/Iro rxRUgcl48im7ZkkEeRykzP975aRFiHWMDYAOLAAK0R2CZ4hRcC3A+j9buEo71ArxWWM4 yffyeWub7wngMWxOs8RFKFl4QbSVzFYrxoz8U6C0wlvtVUh+XBrVw4j6bvoan7Vs0IOC 14rQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704694911; x=1705299711; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=rTagxW2qGB+SOLygMjXPo1Qtb5o4FGjhXHBVBibN0pU=; b=gptP9EiaayLR2OS/lDCIyaiesHNILyXzE0qtOM6+jmbpVAVMQSAVeWr7PhfNBB+Mde wp8Hz+hgzmXDVFbKJIUfd11bjpiukxKIHYB4IULeKmUYVTGl3747vkHEq8sT3vMGaO1O SVmPaHAqfb4WPmucOD0tN1fWn285kA4DSjdaceUtlPPQ8wmTV920rWDm3tCE09+wnpNc UKsj9/wGVUD8uCkrnKASVopKVFTJP/GCtoyh9+MZIemsZnYdh1UATgq6d8amCYfpPQcJ mp8S+TFRCNRWANI7t9HdLWTEXdKejlTSbMTyf/DQxio3CK9+tHmuAYmr2FX6IH6vRH91 KQsw== X-Gm-Message-State: AOJu0YyD36xZHDhSqvjBH0/kKd+YZBpocttylhwYkUI0K1vp6JdF4N+r 5vOZcjM6C+9yry+FD3VrM+fELM5PHs8ZPA== X-Google-Smtp-Source: AGHT+IFa/8crDGiw23IVD1Re4sfunNDvOsjvdYD9ocKdSLdiRngJSe7dZWlLFJzqhXakKcaX9nv6eQ== X-Received: by 2002:a05:6871:341e:b0:1fa:f86b:8624 with SMTP id nh30-20020a056871341e00b001faf86b8624mr904328oac.19.1704694911244; Sun, 07 Jan 2024 22:21:51 -0800 (PST) Received: from charlie.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id i12-20020a9d53cc000000b006dba99e1835sm1274322oth.4.2024.01.07.22.21.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Jan 2024 22:21:50 -0800 (PST) From: Charlie Jenkins Date: Sun, 07 Jan 2024 22:21:45 -0800 Subject: [PATCH v4 1/2] riscv: Include riscv_set_icache_flush_ctx prctl MIME-Version: 1.0 Message-Id: <20240107-fencei-v4-1-d4cf2fb905d3@rivosinc.com> References: <20240107-fencei-v4-0-d4cf2fb905d3@rivosinc.com> In-Reply-To: <20240107-fencei-v4-0-d4cf2fb905d3@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Jonathan Corbet , Conor Dooley , =?utf-8?b?Q2zDqW1lbnQgTMOpZ2Vy?= , Atish Patra Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Charlie Jenkins X-Mailer: b4 0.12.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1704694908; l=7194; i=charlie@rivosinc.com; s=20231120; h=from:subject:message-id; bh=44jA1SP4uAeWO8J8wsxBQ+ZD40NMHu45EJStFpvhUWw=; b=D7UBMh9ebhLewE4U2l7cKbc38/hZBpH6xpofpr+GzFrjeRWkPTAn7+VNKdzVmd8uEW+nIITMh tylX6iA10nEDdAPm3eerU9jJAkXoOSV9+UJ82fUbrUu5dM88k8NUmdj X-Developer-Key: i=charlie@rivosinc.com; a=ed25519; pk=t4RSWpMV1q5lf/NWIeR9z58bcje60/dbtxxmoSfBEcs= X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240107_222153_363793_65BBA748 X-CRM114-Status: GOOD ( 20.56 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Support new prctl with key PR_RISCV_SET_ICACHE_FLUSH_CTX to enable optimization of cross modifying code. This prctl enables userspace code to use icache flushing instructions such as fence.i with the guarantee that the icache will continue to be clean after thread migration. Signed-off-by: Charlie Jenkins --- arch/riscv/include/asm/mmu.h | 2 ++ arch/riscv/include/asm/processor.h | 6 ++++ arch/riscv/mm/cacheflush.c | 56 ++++++++++++++++++++++++++++++++++++++ arch/riscv/mm/context.c | 8 ++++-- include/uapi/linux/prctl.h | 4 +++ kernel/sys.c | 6 ++++ 6 files changed, 79 insertions(+), 3 deletions(-) diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h index 355504b37f8e..60be458e94da 100644 --- a/arch/riscv/include/asm/mmu.h +++ b/arch/riscv/include/asm/mmu.h @@ -19,6 +19,8 @@ typedef struct { #ifdef CONFIG_SMP /* A local icache flush is needed before user execution can resume. */ cpumask_t icache_stale_mask; + /* Force local icache flush on all migrations. */ + bool force_icache_flush; #endif #ifdef CONFIG_BINFMT_ELF_FDPIC unsigned long exec_fdpic_loadmap; diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index f19f861cda54..7eda6c75e0f2 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -84,6 +84,9 @@ struct thread_struct { unsigned long vstate_ctrl; struct __riscv_v_ext_state vstate; unsigned long align_ctl; +#ifdef CONFIG_SMP + bool force_icache_flush; +#endif }; /* Whitelist the fstate from the task_struct for hardened usercopy */ @@ -145,6 +148,9 @@ extern int set_unalign_ctl(struct task_struct *tsk, unsigned int val); #define GET_UNALIGN_CTL(tsk, addr) get_unalign_ctl((tsk), (addr)) #define SET_UNALIGN_CTL(tsk, val) set_unalign_ctl((tsk), (val)) +#define RISCV_SET_ICACHE_FLUSH_CTX(arg1, arg2) riscv_set_icache_flush_ctx(arg1, arg2) +extern int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread); + #endif /* __ASSEMBLY__ */ #endif /* _ASM_RISCV_PROCESSOR_H */ diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c index 55a34f2020a8..f483b6090c27 100644 --- a/arch/riscv/mm/cacheflush.c +++ b/arch/riscv/mm/cacheflush.c @@ -5,6 +5,7 @@ #include #include +#include #include #include @@ -152,3 +153,58 @@ void __init riscv_init_cbo_blocksizes(void) if (cboz_block_size) riscv_cboz_block_size = cboz_block_size; } + +/** + * riscv_set_icache_flush_ctx() - Enable/disable icache flushing instructions in userspace. + * @ctx: Set the type of icache flushing instructions permitted/prohibited. + * + * * %PR_RISCV_CTX_SW_FENCEI_ON: Allow fence.i in userspace. + * + * * %PR_RISCV_CTX_SW_FENCEI_OFF: Disallow fence.i in userspace. When + * ``per_thread == 0``, this will effect all threads in a process. Therefore, + * caution must be taken -- only use this flag when you can guarantee that no + * thread in the process will emit fence.i from this point onward. + * + * @per_thread: When set to 0, will perform operation on process migration. When + * set to 1, will perform operation on thread migration. + * + * When (per_thread == 0), all threads in the process are permitted to emit + * icache flushing instructions. Whenever any thread in the process is migrated, + * the corresponding hart's icache will be guaranteed to be consistent with + * instruction memory. Note this does not enforce any guarantees outside of + * migration. If a thread modifies an instruction that another thread may attempt + * to execute, the other thread must still emit an icache flushing instruction + * before attempting to execute the potentially modified instruction. This must + * be performed by the userspace program. + * + * In per-thread context (eg. per_thread == 1), only the thread calling this + * function is permitted to emit icache flushing instructions. When the thread + * is migrated, the corresponding hart's icache will be guaranteed to be + * consistent with instruction memory. + * + * On kernels configured without SMP, this function is a nop as migrations + * across harts will not occur. + */ +int riscv_set_icache_flush_ctx(unsigned long ctx, unsigned long per_thread) +{ +#ifdef CONFIG_SMP + switch (ctx) { + case PR_RISCV_CTX_SW_FENCEI_ON: + if (per_thread) + current->thread.force_icache_flush = true; + else + current->mm->context.force_icache_flush = true; + break; + case PR_RISCV_CTX_SW_FENCEI_OFF: + if (per_thread) + current->thread.force_icache_flush = false; + else + current->mm->context.force_icache_flush = false; + break; + + default: + break; + } +#endif + return 0; +} diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c index 217fd4de6134..0146c61be0ab 100644 --- a/arch/riscv/mm/context.c +++ b/arch/riscv/mm/context.c @@ -297,12 +297,14 @@ static inline void set_mm(struct mm_struct *prev, * * The "cpu" argument must be the current local CPU number. */ -static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu) +static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu, + struct task_struct *task) { #ifdef CONFIG_SMP cpumask_t *mask = &mm->context.icache_stale_mask; - if (cpumask_test_cpu(cpu, mask)) { + if (cpumask_test_cpu(cpu, mask) || mm->context.force_icache_flush || + (task && task->thread.force_icache_flush)) { cpumask_clear_cpu(cpu, mask); /* * Ensure the remote hart's writes are visible to this hart. @@ -332,5 +334,5 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next, set_mm(prev, next, cpu); - flush_icache_deferred(next, cpu); + flush_icache_deferred(next, cpu, task); } diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 370ed14b1ae0..ec731dda5b8e 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -306,4 +306,8 @@ struct prctl_mm_map { # define PR_RISCV_V_VSTATE_CTRL_NEXT_MASK 0xc # define PR_RISCV_V_VSTATE_CTRL_MASK 0x1f +#define PR_RISCV_SET_ICACHE_FLUSH_CTX 71 +# define PR_RISCV_CTX_SW_FENCEI_ON 0 +# define PR_RISCV_CTX_SW_FENCEI_OFF 1 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index 420d9cb9cc8e..e806a8a67c36 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -146,6 +146,9 @@ #ifndef RISCV_V_GET_CONTROL # define RISCV_V_GET_CONTROL() (-EINVAL) #endif +#ifndef RISCV_SET_ICACHE_FLUSH_CTX +# define RISCV_SET_ICACHE_FLUSH_CTX(a, b) (-EINVAL) +#endif /* * this is where the system-wide overflow UID and GID are defined, for @@ -2739,6 +2742,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_RISCV_V_GET_CONTROL: error = RISCV_V_GET_CONTROL(); break; + case PR_RISCV_SET_ICACHE_FLUSH_CTX: + error = RISCV_SET_ICACHE_FLUSH_CTX(arg2, arg3); + break; default: error = -EINVAL; break; From patchwork Mon Jan 8 06:21:46 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 13513019 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1AB36C3DA6E for ; Mon, 8 Jan 2024 06:22:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:In-Reply-To:References:Message-Id :MIME-Version:Subject:Date:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=5ZZk5G7GQTkrnIODGbhMP9d2S+QU57YayqJ9FOUmIwg=; b=t6QQjHArYHq8Sp GQ6uSj2ZW7QIB3AvUfB4vBhWHMydreUgLh1uLuaSgGDwu642OPcO66eW99y7wk8ucxkT3EfnT6rV/ McezNR8DwMfO8uf+3wgXCwAWQ4BdYQwSWA81Kk6SmemigNTD4rkOSfmHaFmXSn86uM4LXgsm1rDau fj/XingjVzcTzf89fkG7xkWZXpf9l+aVHVCO1UQIIwb1JjXVElG3cuXZn988gQybvyNr80On3fRf9 oyuY2YaBaQWCGsNG63xWPUuo71cGpks69P3SLoiZEAqxwzpurBFi5afAFxYX05qEo9CDQfReTvxoe /E0RQtpLwAewDPAez9TA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rMj1I-0043aZ-1M; Mon, 08 Jan 2024 06:21:56 +0000 Received: from mail-ot1-x332.google.com ([2607:f8b0:4864:20::332]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rMj1F-0043Yi-0X for linux-riscv@lists.infradead.org; Mon, 08 Jan 2024 06:21:55 +0000 Received: by mail-ot1-x332.google.com with SMTP id 46e09a7af769-6dbcc5d78eeso1155087a34.3 for ; Sun, 07 Jan 2024 22:21:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1704694912; x=1705299712; darn=lists.infradead.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=7zIxoN+SgU88Z6qGdoK7DlJzsgAjm+cXBEiUMLpGQcU=; b=0qBGrbaDIWGqLHRm1UmAjOmvUIN8FXvyrMD+nlP+QSFRWtYsn9D8wTaTEUwz0UmmeL Y2sRhgvD+9khuG56bKOfCSXqkJTP7uqq1WBm/jnbszlnHxyD9b0NhJJeB8s5/FLv2zGe gM6MihUOY44nw7ndsh2yzTF+oFkgBZqzQRMfX1x0kk4gXfYX+feRlx+Dokv8rsifggtu eGdLo8pnhLFU9znTDQxapkan9eIv54reVILp3sAtJ1NKYMLK4XN63/0hbeZviuB53Wgh 5XMWrfHyzS+CbAaIofrjGLlcjf2UiV+zt5mAJncKVRkb10vCxtOnqjVCURmlVCbMjFKG XavA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704694912; x=1705299712; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=7zIxoN+SgU88Z6qGdoK7DlJzsgAjm+cXBEiUMLpGQcU=; b=rx8ylaC0ZU913d+AY3Va50RusAo7ib74rkuR+tncaRE5YDQtAliSpleW9ohNF90RJT BlFbOgvEyyv2CE/hprVGVvR4clzt2ZX9dXsMfBEYH4CMot032U5dmugB+7ASxkO39u1T 5yScwAKfeGXJFmjHePvOLNElW4d9mrcSrhia9AFcN3TKsxIUsydAwDZYvKR3WbeUPJDs qKGapQ7LQ/8qjvtrOjYHim2BET+YEhTkHQmXr1JqsAW2a4+kQn2x+qp35Fh6GU7WJCev /ZfL6285rnkWEzHmbD1KlUIrFXmN3ekIGJkywv0Uxg/Evre8nUuuIwl+H3BXmPUsap2/ 3wMQ== X-Gm-Message-State: AOJu0YyDdzLGA6fkiAMx0yYIXRKK4weR4iadlKbwmiwt8QlC+bUfwI2j BTxisqDLJZkdM8N/XSjfmjiKHRtApBXteQ== X-Google-Smtp-Source: AGHT+IE2RD77UZkWItFT81fkRj5KkrLB/kBjCp/AJOn60PTjV5k/LNvDjNw8kS6q6TlbpgWCWHHmgw== X-Received: by 2002:a9d:7a85:0:b0:6db:95ba:c422 with SMTP id l5-20020a9d7a85000000b006db95bac422mr2004194otn.41.1704694912539; Sun, 07 Jan 2024 22:21:52 -0800 (PST) Received: from charlie.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id i12-20020a9d53cc000000b006dba99e1835sm1274322oth.4.2024.01.07.22.21.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Jan 2024 22:21:52 -0800 (PST) From: Charlie Jenkins Date: Sun, 07 Jan 2024 22:21:46 -0800 Subject: [PATCH v4 2/2] documentation: Document PR_RISCV_SET_ICACHE_FLUSH_CTX prctl MIME-Version: 1.0 Message-Id: <20240107-fencei-v4-2-d4cf2fb905d3@rivosinc.com> References: <20240107-fencei-v4-0-d4cf2fb905d3@rivosinc.com> In-Reply-To: <20240107-fencei-v4-0-d4cf2fb905d3@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Jonathan Corbet , Conor Dooley , =?utf-8?b?Q2zDqW1lbnQgTMOpZ2Vy?= , Atish Patra Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Charlie Jenkins X-Mailer: b4 0.12.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1704694908; l=3764; i=charlie@rivosinc.com; s=20231120; h=from:subject:message-id; bh=somI31K4e1DNhLYi544ikiKSJVE5TPTc178CdwxSACE=; b=wOjyNp3Bafs5E4EAXPZDcY5CMZv7eGYP53YeKRTCExbTq0Ej9zlAWZ2834TSECygPHMj+NHYv 9lX1K2SdI/4Dy5Tn8rFusqYzrPJcIbPyqyeQcXJdQVXSC5NuhF6Mkt6 X-Developer-Key: i=charlie@rivosinc.com; a=ed25519; pk=t4RSWpMV1q5lf/NWIeR9z58bcje60/dbtxxmoSfBEcs= X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240107_222153_364392_B2976056 X-CRM114-Status: GOOD ( 17.37 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org Provide documentation that explains how to properly do CMODX in riscv. Signed-off-by: Charlie Jenkins --- Documentation/arch/riscv/cmodx.rst | 88 ++++++++++++++++++++++++++++++++++++++ Documentation/arch/riscv/index.rst | 1 + 2 files changed, 89 insertions(+) diff --git a/Documentation/arch/riscv/cmodx.rst b/Documentation/arch/riscv/cmodx.rst new file mode 100644 index 000000000000..71598850e131 --- /dev/null +++ b/Documentation/arch/riscv/cmodx.rst @@ -0,0 +1,88 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================================================== +Concurrent Modification and Execution of Instructions (CMODX) for RISC-V Linux +============================================================================== + +CMODX is a programming technique where a program executes instructions that were +modified by the program itself. Instruction storage and the instruction cache +(icache) is not guaranteed to be synchronized on RISC-V hardware. Therefore, the +program must enforce its own synchronization with the unprivileged fence.i +instruction. + +However, the default Linux ABI prohibits the use of fence.i in userspace +applications. At any point the scheduler may migrate a task onto a new hart. If +migration occurs after the userspace synchronized the icache and instruction +storage with fence.i, the icache will no longer be clean. This is due to the +behavior of fence.i only affecting the hart that it is called on. Thus, the hart +that the task has been migrated to, may not have synchronized instruction +storage and icache. + +There are two ways to solve this problem: use the riscv_flush_icache() syscall, +or use the ``PR_RISCV_SET_ICACHE_FLUSH_CTX`` prctl() and emit fence.i in +userspace. The syscall performs a one-off icache flushing operation. The prctl +changes the Linux ABI to allow userspace to emit icache flushing operations. + +1. prctl() Interface +--------------------- + +Call prctl() with ``PR_RISCV_SET_ICACHE_FLUSH_CTX`` as the first argument. The +remaining arguments will be delegated to the riscv_set_icache_flush_ctx +function detailed below. + +.. kernel-doc:: arch/riscv/mm/cacheflush.c + :identifiers: riscv_set_icache_flush_ctx + +Example usage: + +The following files are meant to be compiled and linked with each other. The +modify_instruction() function replaces an add with 0 with an add with one, +causing the instruction sequence in get_value() to change from returning a zero +to returning a one. + +cmodx.c:: + + #include + #include + + extern int get_value(); + extern void modify_instruction(); + + int main() + { + int value = get_value(); + printf("Value before cmodx: %d\n", value); + + // Call prctl before first fence.i is called inside modify_instruction + prctl(PR_RISCV_SET_ICACHE_FLUSH_CTX_ON, PR_RISCV_CTX_SW_FENCEI, 0); + modify_instruction(); + + value = get_value(); + printf("Value after cmodx: %d\n", value); + return 0; + } + +cmodx.S:: + + .option norvc + + .text + .global modify_instruction + modify_instruction: + lw a0, new_insn + lui a5,%hi(old_insn) + sw a0,%lo(old_insn)(a5) + fence.i + ret + + .section modifiable, "awx" + .global get_value + get_value: + li a0, 0 + old_insn: + addi a0, a0, 0 + ret + + .data + new_insn: + addi a0, a0, 1 diff --git a/Documentation/arch/riscv/index.rst b/Documentation/arch/riscv/index.rst index 4dab0cb4b900..eecf347ce849 100644 --- a/Documentation/arch/riscv/index.rst +++ b/Documentation/arch/riscv/index.rst @@ -13,6 +13,7 @@ RISC-V architecture patch-acceptance uabi vector + cmodx features