From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 6E80D3612DF for ; Fri, 16 Jan 2026 12:13:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768565582; cv=none; b=nEgFRjx70ygToO0R2r8OltevyZej+xIOWry+LEXbj/+h81y0p3hBcDqiugtbkfNZsxnNmqXqeUvkse5dJAuVZlbdcf0tOT+nsFdwo1EytSuN03EUdIBD4mqG6SuahAYcc2ilO9e7VzimAzTB7KP68lg8j6XuC0I4Enxqq6M9fvY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768565582; c=relaxed/simple; bh=H9aI2Q83iCkWc6TEmnuF/X6GTYeKiJdRfajHWB2Udu0=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=iio3IJf1hwIaRGOwlV5FidgOebQGSe0yZwzm6mXC1lEmQHw498oHrik6vShCHwd6mH/fpifTGfRPnCdAqo9xXwij3bB9YwfSyWcRehahASbB/JD5DDU5IJRqeK+nGbJgFiIBdwezviLVjUwI1P65UJwWsKk8TXFAJVhVOrPUUU8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 20E041515; Fri, 16 Jan 2026 04:12:53 -0800 (PST) Received: from [10.1.196.46] (e134344.arm.com [10.1.196.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 012263F694; Fri, 16 Jan 2026 04:12:54 -0800 (PST) Message-ID: Date: Fri, 16 Jan 2026 12:12:53 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 02/47] arm_mpam: Use non-atomic bitops when modifying feature bitmap From: Ben Horgan To: Catalin Marinas Cc: amitsinght@marvell.com, baisheng.gao@unisoc.com, baolin.wang@linux.alibaba.com, carl@os.amperecomputing.com, dave.martin@arm.com, david@kernel.org, dfustini@baylibre.com, fenghuay@nvidia.com, gshan@redhat.com, james.morse@arm.com, jonathan.cameron@huawei.com, kobak@nvidia.com, lcherian@marvell.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, peternewman@google.com, punit.agrawal@oss.qualcomm.com, quic_jiles@quicinc.com, reinette.chatre@intel.com, rohit.mathew@arm.com, scott@os.amperecomputing.com, sdonthineni@nvidia.com, tan.shaopeng@fujitsu.com, xhao@linux.alibaba.com, will@kernel.org, corbet@lwn.net, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, kvmarm@lists.linux.dev References: <20260112165914.4086692-1-ben.horgan@arm.com> <20260112165914.4086692-3-ben.horgan@arm.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 1/16/26 12:02, Ben Horgan wrote: > Hi Catalin, > > On 1/16/26 11:57, Catalin Marinas wrote: >> On Mon, Jan 12, 2026 at 04:58:29PM +0000, Ben Horgan wrote: >>> In the test__props_mismatch() kunit test we rely on the struct mpam_props >>> being packed to ensure memcmp doesn't consider packing. Making it packed >>> reduces the alignment of the features bitmap and so breaks a requirement >>> for the use of atomics. As we don't rely on the set/clear of these bits >>> being atomic, just make them non-atomic. >>> >>> Reviewed-by: Jonathan Cameron >>> Signed-off-by: Ben Horgan >>> --- >>> Changes since v2: >>> Add comment (Jonathan) >>> --- >>> drivers/resctrl/mpam_internal.h | 8 ++++++-- >>> 1 file changed, 6 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h >>> index 17cdc3080d58..e8971842b124 100644 >>> --- a/drivers/resctrl/mpam_internal.h >>> +++ b/drivers/resctrl/mpam_internal.h >>> @@ -200,8 +200,12 @@ struct mpam_props { >>> } PACKED_FOR_KUNIT; >>> >>> #define mpam_has_feature(_feat, x) test_bit(_feat, (x)->features) >>> -#define mpam_set_feature(_feat, x) set_bit(_feat, (x)->features) >>> -#define mpam_clear_feature(_feat, x) clear_bit(_feat, (x)->features) >>> +/* >>> + * The non-atomic get/set operations are used because if struct mpam_props is >>> + * packed, the alignment requirements for atomics aren't met. >>> + */ >>> +#define mpam_set_feature(_feat, x) __set_bit(_feat, (x)->features) >>> +#define mpam_clear_feature(_feat, x) __clear_bit(_feat, (x)->features) >> >> After discussing privately, I can see how test__props_mismatch() can >> end up with unaligned atomics on the mmap_props::features array. Happy to >> pick it up for 6.19 (probably the first patch as well, though that's >> harmless). > > Yes please. > >> >> Is there a Fixes tag here for future reference? >> > > Yes, the mpam_set/clear macros were introduced in The mpam_set_clear() actually comes after in: c10ca83a7783 arm_mpam: Merge supported features during mpam_enable() into mpam_class but I think the fixes below is still the correct one as it is where we could first start seeing the problem. > > Fixes: 8c90dc68a5de ("arm_mpam: Probe the hardware features resctrl supports") > > Thanks, > > Ben > > Thanks, Ben