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 853F23074BE for ; Thu, 11 Dec 2025 11:23:35 +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=1765452217; cv=none; b=i2Ym9Ew0889AvIaibDse5/s4s8xJebCKxonOCnFCuYAdXL9aRrGCdplX5K7Sst8m1/fb1OrgbCwPe9PrTBpo37Lqkq6tbXbGiENKV8NyUKGODFzw2KRJlXlAnblteADQZ272upLgm7G9/qSylY9V/YHAt4UUFKdeB6x7cCa5tqA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765452217; c=relaxed/simple; bh=GNVMn2VRb3NOTMXfQE8NxHBA2KSAgPmx2WFtQ0sW0Z0=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=k8tx7BIhkH80FFB3/X7sEgDA/iIfwG4Qi9EF9toMuq3x6BRVP5piGrZoW2G1377NRdIhRKvsqIS9+ajVDM8vhv0NJ5uMiGWwEP1s0U3axBm5Tfp3wK3d4ynOnbKEhJw7DZTEBtiYDsniLiVESPfmKV1ljq9R8sYqVwctYKPfgM4= 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 5903B175D; Thu, 11 Dec 2025 03:23:27 -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 41F893F740; Thu, 11 Dec 2025 03:23:31 -0800 (PST) Message-ID: Date: Thu, 11 Dec 2025 11:23:29 +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: [RFC PATCH 02/38] arm64: mpam: Re-initialise MPAM regs when CPU comes online From: Ben Horgan To: James Morse , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , peternewman@google.com, dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Dave Martin , Koba Ko , Shanker Donthineni , fenghuay@nvidia.com, baisheng.gao@unisoc.com, Jonathan Cameron , Gavin Shan , rohit.mathew@arm.com, reinette.chatre@intel.com, Punit Agrawal References: <20251205215901.17772-1-james.morse@arm.com> <20251205215901.17772-3-james.morse@arm.com> <0ea282be-c44f-4562-9104-1efe57348a3e@arm.com> Content-Language: en-US In-Reply-To: <0ea282be-c44f-4562-9104-1efe57348a3e@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi James, On 12/9/25 15:13, Ben Horgan wrote: > Hi James, > > On 12/5/25 21:58, James Morse wrote: >> Now that the MPAM system registers are expected to have values that change, >> reprogram them based on struct task_struct when a CPU is brought online. >> >> Previously MPAM's 'default PARTID' of 0 was used this is the PARTID that >> hardware guarantees to reset. Because there are a limited number of >> PARTID, this value is exposed to user space, meaning resctrl changes >> to the resctrl default group would also affect kernel threads. >> Instead, use the task's PARTID value for kernel work on behalf of >> user-space too. >> >> Signed-off-by: James Morse >> --- >> arch/arm64/kernel/cpufeature.c | 18 +++++++++++------- >> 1 file changed, 11 insertions(+), 7 deletions(-) >> >> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c >> index 5ed401ff79e3..429128a181ac 100644 >> --- a/arch/arm64/kernel/cpufeature.c >> +++ b/arch/arm64/kernel/cpufeature.c >> @@ -86,6 +86,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -2439,13 +2440,16 @@ test_has_mpam(const struct arm64_cpu_capabilities *entry, int scope) >> static void >> cpu_enable_mpam(const struct arm64_cpu_capabilities *entry) >> { >> - /* >> - * Access by the kernel (at EL1) should use the reserved PARTID >> - * which is configured unrestricted. This avoids priority-inversion >> - * where latency sensitive tasks have to wait for a task that has >> - * been throttled to release the lock. >> - */ >> - write_sysreg_s(0, SYS_MPAM1_EL1); >> + int cpu = smp_processor_id(); >> + u64 regval = 0; >> + >> + if (IS_ENABLED(CONFIG_MPAM)) >> + regval = READ_ONCE(per_cpu(arm64_mpam_current, cpu)); > > CONFIG_MPAM -> CONFIG_ARM64_MPAM Actually, this code is only run before the mpam enablement is finished, importantly before the mpam_enabled static key is set, and so arm64_mpam_current is still 0 for every cpu. For cpus that are brought up after boot time this is never run. As SYS_MPAM0_EL1 and SYS_MPAM1_EL1 are unknown out of reset we should set them to 0 whenever a cpu comes online to make sure they initially use PARTID 0 as that is the only one guaranteed to have sensible defaults in the MSC. Once the mpam driver has configured the MSC we can start setting other values. > >> + >> + write_sysreg_s(regval, SYS_MPAM1_EL1); >> + isb(); >> + >> + write_sysreg_s(regval, SYS_MPAM0_EL1); >> } >> >> static bool > > Thanks, > > Ben > > Thanks, Ben