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 63F94348890 for ; Fri, 16 Jan 2026 12:02:18 +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=1768564939; cv=none; b=I5W5S9MrTkG8ZDWfwWyCm5XtV1X9CZ0+A/Ip0IhyxnTP29mWe3jBNRgaD/QeFleHA70UqkXd28UDLId7bGLdwU8PRWcxLnIgp5QuawbamYfJ2q/iS33APPK+hg+XHjaodQ1azyH8MvVO89YJDCZMn4M/nDcC9ISYk7c45KQIy18= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768564939; c=relaxed/simple; bh=6+Ca0QhAGX8M2gTFvtRDV0zLxVN6eYfFHdAEuMNbmrA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TXwh5eRxZP/7j9yj7axn9QXS4gxNQA1OT71O0P3ca7yicrJHJVIzzsqllFVON8S/2OgitxfiMfTtg5IoJxlgtVT4BDxXcctNyRh/CIsFIlCwFxc2QfgQzxwi+O3CRTGMar5+CZrUDtDou4WlxTu/BdqFyl0qj1Go9Ixx9dRxYmk= 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 D19B41515; Fri, 16 Jan 2026 04:02:05 -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 AC0093F694; Fri, 16 Jan 2026 04:02:07 -0800 (PST) Message-ID: Date: Fri, 16 Jan 2026 12:02:06 +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 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> From: Ben Horgan Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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 Fixes: 8c90dc68a5de ("arm_mpam: Probe the hardware features resctrl supports") Thanks, Ben