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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3721C64ED6 for ; Mon, 27 Feb 2023 19:24:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229914AbjB0TYk (ORCPT ); Mon, 27 Feb 2023 14:24:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58760 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229470AbjB0TYi (ORCPT ); Mon, 27 Feb 2023 14:24:38 -0500 Received: from mail-oo1-xc35.google.com (mail-oo1-xc35.google.com [IPv6:2607:f8b0:4864:20::c35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41FE81ADE0; Mon, 27 Feb 2023 11:24:37 -0800 (PST) Received: by mail-oo1-xc35.google.com with SMTP id e12-20020a4ae0cc000000b00525034ca5e9so1179986oot.0; Mon, 27 Feb 2023 11:24:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=OYi4D56fLFAcp+E2w9iavlNCyepBuSBHm3EJC6EjxUM=; b=jp3Iq0qX64RUn1eqPAsL63InclK/VDRgzPVh8LjhRsAUZZYfIZFQQJVap7Jncdbe5Y 1IBYI6npVMXH30FQHuZvNh3bgpjxStRb8swapkt39slyxKYzql+gfXCoIcsmXglOwIPo /n6xM9eRr8DKFE9wnllXbdIJ0044zb+1XM+fCoY8SO8GEs3vuWNVi1aybLbU9RvtteVg JZytuNwZaqKVDGlpgsubZOOkkquqgLN3+SaP72lIi9l2mzikjLOuhBKmzZYBY5MDWSoi rR885eAtSH4rsx94FfYknNN5VhEwsn314rmEq6JNTpYpVcGaBr4ycScEqpex8YOSU9kX MvZg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=OYi4D56fLFAcp+E2w9iavlNCyepBuSBHm3EJC6EjxUM=; b=n4T8WWYVQp+263IKQGiiSBknLfIPsMRlUfBGDC1pVcoK1IOQkq/rYz7IrVUwGFBiiD ALXyjm/Ivj40wptWtGIiLBordtCB/Vas+7Hwibw8tVAfWfDZRkYMyyX588IaWzNLZ/hL 9Yr7Kl1qirLLmjXpdWZSrS/Sdf+AtHDy1VhFH4SPXBbruY8f8cmnvl+cJcCjMqf91YNl ultu92gE8BaAbBxPasFXHne368zkExsrtnFBHkHc5VP96omX4DCQzJR1WiZEl2vAYHo8 CNKoVgFf/bKAoW3eo/2OAU+IJSIQ0wcE65Z899fLzieKOatcuV5QA9q3NfTrUIxpEVsR eGnA== X-Gm-Message-State: AO0yUKXd+kH69F6g2mAAvWbxuUfea2kvneHuyA/91Ql8O3ImJ53XrJvu HtPaSt50hM2tfzKNWZCI5l8= X-Google-Smtp-Source: AK7set/7HxEqLiFg62ktKhMqg2ZASIB55eWr5PN3v12WPb33YrNjI+Gk+K37ug65NjhqA6BhCYm3vQ== X-Received: by 2002:a05:6820:1388:b0:51a:c9a:ee79 with SMTP id i8-20020a056820138800b0051a0c9aee79mr5373604oow.2.1677525876418; Mon, 27 Feb 2023 11:24:36 -0800 (PST) Received: from localhost ([12.97.180.36]) by smtp.gmail.com with ESMTPSA id h9-20020a4aa289000000b005253a5cc3cfsm2946595ool.29.2023.02.27.11.24.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Feb 2023 11:24:35 -0800 (PST) Date: Mon, 27 Feb 2023 11:24:34 -0800 From: Yury Norov To: Guenter Roeck Cc: Alexander Lobakin , linux-kernel@vger.kernel.org, Alexander Gordeev , Alexander Lobakin , Andy Shevchenko , Christian Borntraeger , Claudio Imbrenda , David Hildenbrand , Heiko Carstens , Janosch Frank , Rasmus Villemoes , Sven Schnelle , Vasily Gorbik , linux-s390@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 3/5] lib/bitmap: add test for bitmap_{from,to}_arr64 Message-ID: References: <20220428205116.861003-1-yury.norov@gmail.com> <20220428205116.861003-4-yury.norov@gmail.com> <20230225184702.GA3587246@roeck-us.net> <95377047-6b26-b434-fc90-2289fccc2a0b@intel.com> <19587ea3-e54c-e3b0-5341-eb7ee486474b@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <19587ea3-e54c-e3b0-5341-eb7ee486474b@roeck-us.net> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 27, 2023 at 06:59:12AM -0800, Guenter Roeck wrote: > On 2/27/23 06:46, Alexander Lobakin wrote: > > From: Yury Norov > > Date: Sat, 25 Feb 2023 16:06:45 -0800 > > > > > On Sat, Feb 25, 2023 at 04:05:02PM -0800, Yury Norov wrote: > > > > On Sat, Feb 25, 2023 at 10:47:02AM -0800, Guenter Roeck wrote: > > > > > Hi, > > > > > > > > > > On Thu, Apr 28, 2022 at 01:51:14PM -0700, Yury Norov wrote: > > > > > > Test newly added bitmap_{from,to}_arr64() functions similarly to > > > > > > already existing bitmap_{from,to}_arr32() tests. > > > > > > > > > > > > Signed-off-by: Yury Norov > > > > > > > > > > Ever since this test is in the tree, several of my boot tests show > > > > > lots of messages such as > > > > > > > > > > test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001) > > > > Hmmm, the whole 4 bytes weren't touched. > > > > > > > test_bitmap: bitmap_to_arr64(nbits == 2): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000003) > > > > > test_bitmap: bitmap_to_arr64(nbits == 3): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000007) > > > > This is where it gets worse... > > > > > > > ... > > > > > test_bitmap: bitmap_to_arr64(nbits == 927): tail is not safely cleared: 0xa5a5a5a500000000 (must be 0x000000007fffffff) > > > > > test_bitmap: bitmap_to_arr64(nbits == 928): tail is not safely cleared: 0xa5a5a5a580000000 (must be 0x00000000ffffffff) > > > > I don't see the pattern how the actual result gets generated. But the > > problem is in the bitmap code rather than in the subtest -- "must be"s > > are fully correct. > > > > Given that the 0xa5s are present in the upper 32 bits, it is Big Endian > > I guess? Maybe even 32-bit Big Endian? Otherwise I'd start concerning > > how comes it doesn't reproduce on x86_64s :D > > > > It does reproduce on 32-bit x86 builds, and as far as I can see > it is only seen with 32-bit little endian systems. Hi Guenter, Alexander, I think that the reason for the failures like this: > test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001) is that bitmap_to_arr64 is overly optimized for 32-bit LE architectures. Regarding this: > test_bitmap: bitmap_to_arr64(nbits == 927): tail is not safely cleared: 0xa5a5a5a500000000 (must be 0x000000007fffffff) I am not sure what happens, but because this again happens on 32-bit LE only, I hope the following fix would help too. Can you please check if the patch works for you? I don't have a 32-bit LE machine in hand, and all my 32-bit VMs (arm and i386) refuse to load the latest kernels for some weird reason, so it's only build-tested. I'll give it a full-run when restore my 32-bit setups. Thanks, Yury >From 2881714db497aed103e310865da075e7b0ce7e1a Mon Sep 17 00:00:00 2001 From: Yury Norov Date: Mon, 27 Feb 2023 09:21:59 -0800 Subject: [PATCH] lib/bitmap: drop optimization of bitmap_{from,to}_arr64 bitmap_{from,to}_arr64() optimization is overly optimistic on 32-bit LE architectures when it's wired to bitmap_copy_clear_tail(). bitmap_copy_clear_tail() takes care of unused bits in the bitmap up to the next word boundary. But on 32-bit machines when copying bits from bitmap to array of 64-bit words, it's expected that the unused part of a recipient array must be cleared up to 64-bit boundary, so the last 4 bytes may stay untouched. While the copying part of the optimization works correct, that clear-tail trick makes corresponding tests reasonably fail when nbits % 64 <= 32: test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001) Fix it by removing bitmap_{from,to}_arr64() optimization for 32-bit LE arches. Reported-by: Guenter Roeck Fixes: 0a97953fd2210 ("lib: add bitmap_{from,to}_arr64") Signed-off-by: Yury Norov --- include/linux/bitmap.h | 8 +++----- lib/bitmap.c | 2 +- 2 files changed, 4 insertions(+), 6 deletions(-) diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index 40e53a2ecc0d..5abc993903fb 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -302,12 +302,10 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, #endif /* - * On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32 - * machines the order of hi and lo parts of numbers match the bitmap structure. - * In both cases conversion is not needed when copying data from/to arrays of - * u64. + * On 64-bit systems bitmaps are represented as u64 arrays internally. So, + * conversion is not needed when copying data from/to arrays of u64. */ -#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN) +#if BITS_PER_LONG == 32 void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits); void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits); #else diff --git a/lib/bitmap.c b/lib/bitmap.c index 1c81413c51f8..ddb31015e38a 100644 --- a/lib/bitmap.c +++ b/lib/bitmap.c @@ -1495,7 +1495,7 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits) EXPORT_SYMBOL(bitmap_to_arr32); #endif -#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN) +#if BITS_PER_LONG == 32 /** * bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap * @bitmap: array of unsigned longs, the destination bitmap -- 2.34.1