From patchwork Tue Jan 9 18:43:25 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 13515255 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 D040CC47079 for ; Tue, 9 Jan 2024 18:43:45 +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=/eG5/ksLmIgSld+D+pkVMG1TvtqfQeLOmwRS9RQAFkw=; b=mcLmia9cpYIqVA 1th770K1VqPe6ydRLy6wUPJmG6uhjzxDrFgQdXdd9iKmiV+4+Wzt7m57GxB47MRktkxNZoS/Jcwsy FMFjUXTFxb8CxiHk2ewiNIkwKDzG4fOqOTYOgumFuDgVvKo7C4HYHHVB5ayTjjbnEoC3du9AMxy7v WEl7DFu0LuBdTMYaPC70mdMGbIpX2MIJA+cdEiJ54B8Lw2tRbl3di4gbCEy79ybEpFPuGZhDBwKrJ zaQEyrYXN4lZmcG65AwA5i1UlzZ6fB98pfLDRZ123Zf8T6hUyFWicIPizxmavhzg9R47o2+Wtr65c /kFdpaYxbijPInrzX2LQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rNH4b-009CHC-3B; Tue, 09 Jan 2024 18:43:37 +0000 Received: from mail-oa1-x2e.google.com ([2001:4860:4864:20::2e]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rNH4V-009CDm-1e for linux-riscv@lists.infradead.org; Tue, 09 Jan 2024 18:43:35 +0000 Received: by mail-oa1-x2e.google.com with SMTP id 586e51a60fabf-204e52f0617so1944993fac.1 for ; Tue, 09 Jan 2024 10:43:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1704825809; x=1705430609; 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=G3cjpRu3f6zFWz4uAdg2rrkRvvrYXJuhrMLKUoKpeZs=; b=MdMVnBWZsORkD4MhQOd+3rSqc0Ls7/94IZLXgnLxKGtQyhFwR/DUw0VF3l3bW/3cIE Tn5Y5UBqxgZqYcylLAFJUuiILAbNpM4t08rKm7Fmy7yNEJRY8RvZM2BTJcf+xGtEl5W3 tWYxvnigLLWzd54rusOt14ChKozCpa11bC85hOXkR2uVj+Op5O8OnJD/z2Zd6WJBe2wo cT3TEJu+I8oS/KAta1NziTjf4Wen3x+cCOgDSDyxu6CU2LFkys96k3xG8Auicuh8cpln 6PHgBoFsfnaj45dKxQSOoeMzSfX63vG5EcaxPMUPEjk6b4o0TV3AWBGnzAUm2HxlAtLc pzdg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704825809; x=1705430609; 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=G3cjpRu3f6zFWz4uAdg2rrkRvvrYXJuhrMLKUoKpeZs=; b=h/alGfm0VXpsHqB029pwXaGR2MUL9PY8E3jUwme7MFbkXoI/QuQh4TXpkAiueyDSdP n8AGH1qanxpZG0Kb25/hG+gkZaYUcY8U09QiR9Cu5CDj6t6A8sdS1A4U3t7O5aAKm8eR laPosKq8RYU+yh0b3zP4l31bPpLfbU6gfhMXyhnwRtWZHcwO3FkzAdf7WwT13QXLve1p 4ermQ7Bp1v81Zkq4YZnf5Y7SWWBkw6Fb8WRU63qe+cbVaARe6FVyuhKRPhm7zax7T3iM ovYUlLkeCTNyUCS+PqRxGNfhPScKlgOIkPuEV0/DIgtYktNgggiyuyqDhKc+RpXb7jjv bM5w== X-Gm-Message-State: AOJu0YyEowM1kg+OjiORG8o4y1Y3jO/a+jcoPkrOenaoZXN9pWE0UKvW 0chjXDy/75vKtHPys9fUTnhTsRYLZBxTuA== X-Google-Smtp-Source: AGHT+IHrDB4IIs7ZxA0Z2AenxMPpG0+0F7QsUHERMVXYyG83tPDIOZuKSGt04ux7GFAVItckjOT4vQ== X-Received: by 2002:a05:6870:40cf:b0:206:d2a:c042 with SMTP id l15-20020a05687040cf00b002060d2ac042mr539386oal.14.1704825809224; Tue, 09 Jan 2024 10:43:29 -0800 (PST) Received: from charlie.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id j2-20020a9d7682000000b006ce2c31dd9bsm450423otl.20.2024.01.09.10.43.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jan 2024 10:43:28 -0800 (PST) From: Charlie Jenkins Date: Tue, 09 Jan 2024 10:43:25 -0800 Subject: [PATCH v6 1/2] riscv: Include riscv_set_icache_flush_ctx prctl MIME-Version: 1.0 Message-Id: <20240109-fencei-v6-1-04116e51445c@rivosinc.com> References: <20240109-fencei-v6-0-04116e51445c@rivosinc.com> In-Reply-To: <20240109-fencei-v6-0-04116e51445c@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Jonathan Corbet , Conor Dooley , =?utf-8?b?Q2zDqW1lbnQgTMOpZ2Vy?= , Atish Patra , Randy Dunlap Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Charlie Jenkins , Atish Patra X-Mailer: b4 0.12.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1704825806; l=7286; i=charlie@rivosinc.com; s=20231120; h=from:subject:message-id; bh=TMJhxlQFfyupgZvbn02F0jv2sXrFhaiDb8k1RNetu6U=; b=9lGgqCoRZPt9fueeDpMrOQWRVLbrg/AMAOvXBWfG+XzK9uC34gHT5GdZMdrtwG8nVc4IK61Xq s6uC+NcVJRzCS8IpMYRbZYm7ZIvVf0syLZhcssA7oKLw+NUBTWj07vE 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-20240109_104331_561524_7868E9A6 X-CRM114-Status: GOOD ( 20.53 ) 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 Reviewed-by: Atish Patra --- arch/riscv/include/asm/mmu.h | 2 ++ arch/riscv/include/asm/processor.h | 6 ++++ arch/riscv/mm/cacheflush.c | 58 ++++++++++++++++++++++++++++++++++++++ arch/riscv/mm/context.c | 8 ++++-- include/uapi/linux/prctl.h | 4 +++ kernel/sys.c | 6 ++++ 6 files changed, 81 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..bac7737b0f47 100644 --- a/arch/riscv/mm/cacheflush.c +++ b/arch/riscv/mm/cacheflush.c @@ -5,6 +5,7 @@ #include #include +#include #include #include @@ -152,3 +153,60 @@ 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. + * + * Supported values for ctx: + * + * * %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 storage. 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 storage. + * + * 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 Tue Jan 9 18:43:26 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charlie Jenkins X-Patchwork-Id: 13515254 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 576D6C46CD2 for ; Tue, 9 Jan 2024 18:43:44 +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=PJZJ3ynHkMaY25YRpkNfsom6a+SXBaG8GbRw3bMUJao=; b=CCO4HavinXRJCw LOxNzECxs9D96KfJBYKdIaTu8S/57c7e5RplPaxJelXrluSMcMZlBRtuL7XXLRyzQPXgpa7EegbA8 zKWMUAtAqTkoP83SPiot95Ag/+3BbRnCkcMTTRyih2TM3WpBcCPcgm++oSmsnbnT7DGCy4R6Vk3Ml j5ayX6/ZzNocmHK5bf+qi9cD7QEkywMmZLkshEI0E2arWCZrb+PxGtW6EdSq6sAKXSXbbc+/6pUWi qnnAqd2QLHOz62CKpCeG/91N7u+aTjhS19CxnjJ4lXv6XLRW1A1lkaaNkDx2Q7xPXQrSRwyx3wJWB 8zn5g78XLJRm8iSi88Jw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rNH4b-009CGS-0O; Tue, 09 Jan 2024 18:43:37 +0000 Received: from mail-oa1-x2a.google.com ([2001:4860:4864:20::2a]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rNH4V-009CE0-1U for linux-riscv@lists.infradead.org; Tue, 09 Jan 2024 18:43:34 +0000 Received: by mail-oa1-x2a.google.com with SMTP id 586e51a60fabf-2041c292da8so1769987fac.3 for ; Tue, 09 Jan 2024 10:43:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1704825810; x=1705430610; 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=H1NNXG/cc6Ss9zFsC2xjmXCCDBeblJidGJDKM2XVVV0=; b=GiOhGIiLWs0axDrwd18tQMG2ygh4mAFOx2lnFyM6o8cYM+RBDYD5Q3/U4vY7sTCz8c iMmrzcumn1DA/KouCe/IeQpwMdchgEvFrEWe8+s01X8zFtS7oU51Mr8TWK9cKQY8pQOH TvNawRN42xZZCZnk1ZLRmaDaYhVwut7iVgTh0Gj0jbq0tD1IRM/y1w59UwHekByOhiKy TpXSG65m2MYIclKeXZxtKyI6DwvxxXqPcNYz5C7MZ1hg2BYsVQrMYJpdukTsqOI0hyyX pOsREvqsysGGb1tSmTaV0+TthQCwivUfUQiAkJ1gM0y9SuR4um5KZH/ZB/CJzs/2+3m3 0SJw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704825810; x=1705430610; 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=H1NNXG/cc6Ss9zFsC2xjmXCCDBeblJidGJDKM2XVVV0=; b=nKgwGJMuNQp/P9W/+WYweI5ZaY4Blca2BHnsU/CQhhr9AHbmmk4W5bxNutA24dQlab X22ict0rCmPZGF8R+aZJY5xbbmSA6WSMhL7RzO9iGGxU7dP/Tr0b2bZR3Mo0FtLKqtC/ uH3nW+pWYE8+euLoYSreiaz3UBMVxWtZ1Kb4JMyRnTwlwl78MB5okuFdJrh8VLJMNVxr 8xqRT1zCcfOCX5I9v0fITDiTFJuNXLfDOiaK/WvcpdNMNjFHae+ByVEadp0sZLinqTrp GC/e6vmn2Aj8lE92VrXTL8UwF3qirwGOhfw5v6OVMJ6UISpKmDc2FkxUGdj65I0S4jxL 9U8A== X-Gm-Message-State: AOJu0Ywu9dywFo8o1DtHkg2LK8SbcUPboNJXyz2kxwHyUczQsGLEjyBG 9RSOvFtoXhOSVu8+AQoS8e54wWY9Q1qHmQ== X-Google-Smtp-Source: AGHT+IGQlBFgMVz5mTuTuO8bTSRghm89zYg7Wg6yrGXtc9FJWyLD8udHcY6dup6zfxmsWGuwNK74iQ== X-Received: by 2002:a05:6870:7884:b0:203:18e9:804a with SMTP id hc4-20020a056870788400b0020318e9804amr6057763oab.86.1704825810491; Tue, 09 Jan 2024 10:43:30 -0800 (PST) Received: from charlie.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id j2-20020a9d7682000000b006ce2c31dd9bsm450423otl.20.2024.01.09.10.43.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jan 2024 10:43:30 -0800 (PST) From: Charlie Jenkins Date: Tue, 09 Jan 2024 10:43:26 -0800 Subject: [PATCH v6 2/2] documentation: Document PR_RISCV_SET_ICACHE_FLUSH_CTX prctl MIME-Version: 1.0 Message-Id: <20240109-fencei-v6-2-04116e51445c@rivosinc.com> References: <20240109-fencei-v6-0-04116e51445c@rivosinc.com> In-Reply-To: <20240109-fencei-v6-0-04116e51445c@rivosinc.com> To: Paul Walmsley , Palmer Dabbelt , Albert Ou , Jonathan Corbet , Conor Dooley , =?utf-8?b?Q2zDqW1lbnQgTMOpZ2Vy?= , Atish Patra , Randy Dunlap Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Charlie Jenkins , Atish Patra X-Mailer: b4 0.12.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1704825806; l=3808; i=charlie@rivosinc.com; s=20231120; h=from:subject:message-id; bh=ABgVzoDksDxj5OqFX0a7CWpy1eY9QNcsIJ1Zy7mwIys=; b=j5GVuprP0qn0h0qUpUY2k2ew7NlFi46kdG1k0oqIUc112oHNCCD9SA9tXCDEIg4X1qkZqh5ZH tINoTxCG7+yAyv173/RET8VuEsm9gqic+JA7gneMpiQeImMmqHv0Dot 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-20240109_104331_526970_DC667261 X-CRM114-Status: GOOD ( 17.69 ) 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 Reviewed-by: Atish Patra --- 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..afd7086c222c --- /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) are 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. + +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