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 789951A285 for ; Mon, 19 Jan 2026 15:49:12 +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=1768837753; cv=none; b=ZXiP/SLtf+PCeHjO/tdAJLkBtGQeEmONND1ebh+gVyCl6OTErgJhWCtuExpmYH9mA2vMPnmNbgIJPDkNvRxGR0yROwNTGxv/6t/ZeEwbE1hhCtcZx7LTjkjoO2CHdBcO9zlQFKNnjk2c1sEUtvC2m37SD0Jhz3BBECj35e45vgA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768837753; c=relaxed/simple; bh=VsMuGxZCEzmxbo4QGjmxWPDX3WL57Yk7hKYyVMqAt/Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tLBZqIl2kIf7Je30WP+3PXuWbRRWzYxE2/jVzf0ksxXD1agok1fX9ZPSjuYbRwb5dpewaT76vZh0dEaewMiVTVSWa5cBW/ifdl04c31NBaL8w/8otTVDOHX9/MrPxSOgw3wMbzgv9ispR07A77T0BrH3rcSuV5hqlFxLyYKl4L0= 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 322B1FEC; Mon, 19 Jan 2026 07:49:05 -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 F2FA93F694; Mon, 19 Jan 2026 07:49:06 -0800 (PST) Message-ID: Date: Mon, 19 Jan 2026 15:49:05 +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 11/47] arm64: mpam: Add helpers to change a task or cpu's MPAM PARTID/PMG values To: Gavin Shan 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, 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, catalin.marinas@arm.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> <20260112165914.4086692-12-ben.horgan@arm.com> <57a015c3-9a4b-478b-8cb6-6c61f84c0b74@redhat.com> From: Ben Horgan Content-Language: en-US In-Reply-To: <57a015c3-9a4b-478b-8cb6-6c61f84c0b74@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Gavin, On 1/19/26 07:01, Gavin Shan wrote: > Hi Ben, > > On 1/13/26 12:58 AM, Ben Horgan wrote: >> From: James Morse >> >> Care must be taken when modifying the PARTID and PMG of a task in any >> per-task structure as writing these values may race with the task being >> scheduled in, and reading the modified values. >> >> Add helpers to set the task properties, and the CPU default value.  These >> use WRITE_ONCE() that pairs with the READ_ONCE() in mpam_get_regval() to >> avoid causing torn values. >> >> CC: Dave Martin >> Reviewed-by: Jonathan Cameron >> Signed-off-by: James Morse >> Signed-off-by: Ben Horgan >> --- >> Changes since rfc: >> Keep comment attached to mpam_get_regval() >> Add internal helper, __mpam_regval() (Jonathan) >> --- >>   arch/arm64/include/asm/mpam.h | 28 ++++++++++++++++++++++++++++ >>   1 file changed, 28 insertions(+) >> >> diff --git a/arch/arm64/include/asm/mpam.h b/arch/arm64/include/asm/ >> mpam.h >> index 7b3d3abad162..c9b73f1af7ce 100644 >> --- a/arch/arm64/include/asm/mpam.h >> +++ b/arch/arm64/include/asm/mpam.h >> @@ -4,6 +4,7 @@ >>   #ifndef __ASM__MPAM_H >>   #define __ASM__MPAM_H >>   +#include >>   #include >>   #include >>   #include >> @@ -22,6 +23,22 @@ DECLARE_PER_CPU(u64, arm64_mpam_current); >>    */ >>   extern u64 arm64_mpam_global_default; >>   +static inline u64 __mpam_regval(u16 partid_d, u16 partid_i, u8 >> pmg_d, u8 pmg_i) >> +{ >> +    return FIELD_PREP(MPAM0_EL1_PARTID_D, partid_d) | >> +        FIELD_PREP(MPAM0_EL1_PARTID_I, partid_i) | >> +        FIELD_PREP(MPAM0_EL1_PMG_D, pmg_d) | >> +        FIELD_PREP(MPAM0_EL1_PMG_I, pmg_i); >> +} > > Nitpick: Alignment issues in the lines for 2nd/3rd/4th FIELD_PREP(). > >     return FIELD_PREP(...) | >            FIELD_PREP(...) | >                FIELD_PREP(...) | >                FIELD_PREP(...); Sure, I'll align these. > >> + >> +static inline void mpam_set_cpu_defaults(int cpu, u16 partid_d, u16 >> partid_i, >> +                     u8 pmg_d, u8 pmg_i) >> +{ >> +    u64 default_val = __mpam_regval(partid_d, partid_i, pmg_d, pmg_i); >> + >> +    WRITE_ONCE(per_cpu(arm64_mpam_default, cpu), default_val); >> +} >> + > > per_cpu(arm64_mpam_default) won't be reachable until CONFIG_ARM64_MPAM > is set. > So I think both mpam_set_cpu_defaults() and __mpam_regval() need to be > protected > by '#ifdef CONFIG_ARM64_MPAM ... #endif'. I'll move the #ifdef CONFIG_ARM64_MPAM up to cover these. > >>   /* >>    * The resctrl filesystem writes to the partid/pmg values for >> threads and CPUs, >>    * which may race with reads in mpam_thread_switch(). Ensure only >> one of the old >> @@ -36,6 +53,17 @@ static inline u64 mpam_get_regval(struct >> task_struct *tsk) >>       return READ_ONCE(task_thread_info(tsk)->mpam_partid_pmg); >>   } >>   +static inline void mpam_set_task_partid_pmg(struct task_struct *tsk, >> +                        u16 partid_d, u16 partid_i, >> +                        u8 pmg_d, u8 pmg_i) >> +{ >> +#ifdef CONFIG_ARM64_MPAM >> +    u64 regval = __mpam_regval(partid_d, partid_i, pmg_d, pmg_i); >> + >> +    WRITE_ONCE(task_thread_info(tsk)->mpam_partid_pmg, regval); >> +#endif >> +} >> + >>   static inline void mpam_thread_switch(struct task_struct *tsk) >>   { >>       u64 oldregval; > > Thanks, > Gavin > Thanks, Ben