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b=sDFuat9oZP6Zmr7jzs7wwrnobKwzF3ije1TfL9rdARCHAOuQuQzbEHlsQmX8TmFVwMnu6+o6N+hSc/bKlnBxIRy9IZvRFikQ6eTVLtcfF3RVbeF61N/MHHYE+zNRkSGEilwCDcMWuG33kh+LoWm1mWHA/CHAhIhMAxIXjJrtGbg= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from BL1PR12MB5320.namprd12.prod.outlook.com (2603:10b6:208:314::17) by SA5PPF8BD1FB094.namprd12.prod.outlook.com (2603:10b6:80f:fc04::8d3) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.92.18; Thu, 11 Jun 2026 21:02:40 +0000 Received: from BL1PR12MB5320.namprd12.prod.outlook.com ([fe80::1876:4a6d:2cf5:b8d1]) by BL1PR12MB5320.namprd12.prod.outlook.com ([fe80::1876:4a6d:2cf5:b8d1%5]) with mapi id 15.21.0113.013; Thu, 11 Jun 2026 21:02:38 +0000 Message-ID: Date: Thu, 11 Jun 2026 16:02:35 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/4] x86,fs/resctrl: kernel-mode (PLZA) fixes found during review To: Qinyun Tan Cc: tony.luck@intel.com, reinette.chatre@intel.com, james.morse@arm.com, Dave.Martin@arm.com, tglx@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org, feng.tang@linux.alibaba.com, xlpang@linux.alibaba.com References: <20260611111706.1981788-1-qinyuntan@linux.alibaba.com> Content-Language: en-US From: Babu Moger In-Reply-To: <20260611111706.1981788-1-qinyuntan@linux.alibaba.com> Content-Type: text/plain; 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The patches are ordered by dependency (build fix > -> semantic fix -> the two binding fixes) so the series is bisectable on > top of v3. > > Patch 1 (ARM MPAM build fix): fs/resctrl now calls > resctrl_arch_get_kmode_support()/resctrl_arch_configure_kmode(), which > are only implemented on x86, so an aarch64 allyesconfig (MPAM) fails to > link. Add empty arch stubs, and hide info/kernel_mode on platforms that > advertise no mode beyond inherit_ctrl_and_mon. > > Patch 2 (RMID_EN + RDTMON_GROUP): RMID_EN is hardcoded to 1, so > inherit_mon counts kernel-mode traffic under the PLZA RMID instead of > inheriting from PQR_ASSOC; and assign_mon is forced to bind an > RDTMON_GROUP, wasting an RMID. Make RMID_EN mode-based and let assign_mon > also accept a control group. This is the issue we discussed earlier and > you confirmed; this is the patch for it. > > Patch 3 (atomic switch): resctrl_kernel_mode_write() releases the > previous binding before it programs the new one. If programming the new > binding fails (-ENOMEM, or a pseudo-locked target group), the old, > working binding is already gone -- a user who only tried to switch loses > the original configuration too. Make the switch atomic: all fallible > work is done before the old binding is released, so a failed switch is a > no-op. > > Patch 4 (CPU online): the PLZA MSR is per-CPU and is only written over > the CPUs that are online at bind time / mask change; nothing reprograms a > CPU that comes online afterwards. A hot-added vCPU, or a CPU that was > offline at bind time, then runs with PLZA off although it is in scope, > while info/kernel_mode still reports the binding as active. Drive the > per-CPU state from resctrl_online_cpu() so it is synced idempotently on > every online (and stale enable bits are cleared for a CPU that left the > scope while offline). > > Concretely, the patch 4 failure mode is: offline a CPU, bind a > global-assign mode while it is absent, then online it -- the onlined CPU > is left with PLZA_EN=0 although it is in scope, while a CPU that was > present at bind time has PLZA_EN=1, so its CPL0 traffic is not accounted > to the bound kernel-mode group. > > I'd appreciate your view on whether these match your intent for the > design. > > Qinyun Tan (4): > resctrl: Add kmode arch stubs for ARM MPAM and hide kernel_mode on > non-PLZA platforms > resctrl: Fix PLZA RMID_EN to be mode-based and relax RDTMON_GROUP > constraint for assign_mon > fs/resctrl: make a failed kernel-mode switch a no-op > fs/resctrl: program PLZA on a CPU that comes online under a binding I have gone thru all your patches. Patches look good to me. I also ran some basic tests to make sure it works as expected. Note the I am still waiting for comments from maintainer (Reinette). I will fold your changes in v4 whenever that happens. Thanks for the review and changes. Thanks Babu