From mboxrd@z Thu Jan 1 00:00:00 1970 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 5F83EF44847 for ; Fri, 10 Apr 2026 12:20:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Type:MIME-Version: References:Subject:Cc:To:From:Message-ID:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To: List-Owner; bh=SzqmkoHD6RR/VnMu1Lp5RPrviQ3U1+g7qyWPaG+gRfs=; b=zcaSbxYuIfa0oI Qpdnm+xqt3sCdDQ55eM3WloZ71tIw1Htg1Jnh+FhJ+Eg02Vkf59D9UqJJpTZLghOtZPYjrRSd0dVS AkflLQysb35dxynl3Ip8rT1kReNrg4AHGOtQ654IvoHQUE/rPr8245u7oj7bxaqCVneHVwboVBvKg 9vTYi3mMTRlEu0ijsnHR2dOVItQGI51iRjWeEVZAd/xfuzNdvnp3QGMmh6hRScV680CMXpUa/YFkD xF2/sC4rUS0M1ne2vc1SEUrK/7acJSrWUDtnsUos5WpIjKkj7PGEPb2n+sq5EJFVKHcIXtCTOx3eP teqiJpTz2yfM/1VUsFfw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1wBAqF-0000000CAoa-39ge; Fri, 10 Apr 2026 12:20:07 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1wBAqD-0000000CAlc-2wqi; Fri, 10 Apr 2026 12:20:05 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 0D8F661332; Fri, 10 Apr 2026 12:20:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1939C19425; Fri, 10 Apr 2026 12:20:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775823604; bh=OJyrwmrX6lIri0LIdsFu5GdqSG8VG/nHQeslgTl5R4k=; h=Date:From:To:Cc:Subject:References:From; b=SQFHopbFA4avzkQltPCDvONKOyWmV73pxkcg27G4tKW1mNfy7PYVk0h6FRJhlowhk TQQGbFN8xcNa+loyfTw/Ao/LMW9fb2z9STU9hSKk0Q9e4TyhUmpic8YPBLcUkWvS5H AbfS/R5YsMQyaoKc/WDlm6lhBx4bXYBfs3B4LA3Z/Y/SjzAwbFrEIx6rz/PfITLKPl d1tT7WhENbDQpyhAelqaE4x97qqSWFBpW6gFyL/Wzy4bWcES9cochVgZgvdNMg3UtL W9F79+f3Gx3pjpImzUkKb/YiEF7KogJM+PPf5Wjs2H8jaVYTBcG1Ittd3E5H9zOpng +M493bQX3+83g== Date: Fri, 10 Apr 2026 14:20:01 +0200 Message-ID: <20260410120318.862164111@kernel.org> User-Agent: quilt/0.68 From: Thomas Gleixner To: LKML Cc: Marco Elver , Dmitry Vyukov , kasan-dev@googlegroups.com, Arnd Bergmann , x86@kernel.org, Lu Baolu , iommu@lists.linux.dev, Michael Grzeschik , netdev@vger.kernel.org, linux-wireless@vger.kernel.org, Herbert Xu , linux-crypto@vger.kernel.org, Vlastimil Babka , linux-mm@kvack.org, David Woodhouse , Bernie Thompson , linux-fbdev@vger.kernel.org, "Theodore Tso" , linux-ext4@vger.kernel.org, Andrew Morton , Uladzislau Rezki , Andrey Ryabinin , Thomas Sailer , linux-hams@vger.kernel.org, "Jason A. Donenfeld" , Richard Henderson , linux-alpha@vger.kernel.org, Russell King , linux-arm-kernel@lists.infradead.org, Catalin Marinas , Huacai Chen , loongarch@lists.linux.dev, Geert Uytterhoeven , linux-m68k@lists.linux-m68k.org, Dinh Nguyen , Jonas Bonn , linux-openrisc@vger.kernel.org, Helge Deller , linux-parisc@vger.kernel.org, Michael Ellerman , linuxppc-dev@lists.ozlabs.org, Paul Walmsley , linux-riscv@lists.infradead.org, Heiko Carstens , linux-s390@vger.kernel.org, "David S. Miller" , sparclinux@vger.kernel.org Subject: [patch 19/38] kcsan: Replace get_cycles() usage References: <20260410120044.031381086@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-BeenThere: linux-arm-kernel@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-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org KCSAN uses get_cycles() for two purposes: 1) Seeding the random state with get_cycles() is a historical leftover. 2) The microbenchmark uses get_cycles(), which provides an unit less counter value and is not guaranteed to be functional on all systems/platforms. Use random_get_entropy() for seeding the random state and ktime_get() which is universaly functional and provides at least a comprehensible unit. This is part of a larger effort to remove get_cycles() usage from non-architecture code. Signed-off-by: Thomas Gleixner Cc: Marco Elver Cc: Dmitry Vyukov Cc: kasan-dev@googlegroups.com --- kernel/kcsan/core.c | 2 +- kernel/kcsan/debugfs.c | 8 ++++---- 2 files changed, 5 insertions(+), 5 deletions(-) --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -798,7 +798,7 @@ void __init kcsan_init(void) BUG_ON(!in_task()); for_each_possible_cpu(cpu) - per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles(); + per_cpu(kcsan_rand_state, cpu) = (u32)random_get_entropy(); /* * We are in the init task, and no other tasks should be running; --- a/kernel/kcsan/debugfs.c +++ b/kernel/kcsan/debugfs.c @@ -58,7 +58,7 @@ static noinline void microbenchmark(unsi { const struct kcsan_ctx ctx_save = current->kcsan_ctx; const bool was_enabled = READ_ONCE(kcsan_enabled); - u64 cycles; + ktime_t nsecs; /* We may have been called from an atomic region; reset context. */ memset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx)); @@ -70,16 +70,16 @@ static noinline void microbenchmark(unsi pr_info("%s begin | iters: %lu\n", __func__, iters); - cycles = get_cycles(); + nsecs = ktime_get(); while (iters--) { unsigned long addr = iters & ((PAGE_SIZE << 8) - 1); int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC : (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0); __kcsan_check_access((void *)addr, sizeof(long), type); } - cycles = get_cycles() - cycles; + nsecs = ktime_get() - nsecs; - pr_info("%s end | cycles: %llu\n", __func__, cycles); + pr_info("%s end | nsecs: %llu\n", __func__, nsecs); WRITE_ONCE(kcsan_enabled, was_enabled); /* restore context */