From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2571E3BF677; Fri, 10 Apr 2026 12:20:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775823605; cv=none; b=qAEsLr+ARlGHU00sd/hZB91g3Roa4iNgJLPWUMJlTPsSgVNfkwM97pJiiVFC9WH5WSI4NB+B0chDWNVdHsM9LH4tAriaNzcASZiGOpLWbdhzorJP0k04SN1Ftt3VA00PMwL/DXAC59QlxDI5asHxnlwDWUodAlOnswAqy2bsLZo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775823605; c=relaxed/simple; bh=OJyrwmrX6lIri0LIdsFu5GdqSG8VG/nHQeslgTl5R4k=; h=Date:Message-ID:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=f8C69ZHYHqVaEEHCSz+BSHpPYfiyYeeTsesnva9tF6yMftVVeI/ci7D4MORtVDPSeyLCiM3pAxA+iZVuD0FypQssGdw3DvMwptXmm3D5gPd9Eau20LT+pNwAYWaWjskwcz9LEKMbeGBrvAi9pRpi2/Lex5ISPxpbmzli6c55EMs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SQFHopbF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SQFHopbF" 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> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 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 */