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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-84edc29c73bsm4431143b3a.29.2026.08.03.20.58.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Aug 2026 20:58:48 -0700 (PDT) Message-ID: Date: Tue, 4 Aug 2026 13:58:37 +1000 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 v7 08/11] arm_mpam: prepare mon_sel locking for MPAM-Fb To: Andre Przywara , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , "Rafael J . Wysocki" , Len Brown , James Morse , Ben Horgan , Reinette Chatre , Fenghua Yu Cc: Jonathan Cameron , Srivathsa L Rao , Ganapatrao Kulkarni , Trilok Soni , Srinivas Ramana , Niyas Sait , Lee Trager , Ritwick Sharma , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260731170324.2927758-1-andre.przywara@arm.com> <20260731170324.2927758-9-andre.przywara@arm.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20260731170324.2927758-9-andre.przywara@arm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/1/26 3:03 AM, Andre Przywara wrote: > The MSC MON_SEL register needs to be accessed from hardirq for the overflow > interrupt, and when taking an IPI to access these registers on platforms > where MSCs are not accesible from every CPU. This makes an irqsave > spinlock the obvious lock to protect these registers. On systems with > MPAM-Fb mailbox MSC access it must be able to sleep, meaning a mutex must > be used. So MPAM-Fb platforms cannot support an overflow interrupt easily. > Clearly these two methods can't exist for one MSC at the same time. > > Change the mon_sel locking wrapper function to only use a spinlock when > the MSC is accessed directly via MMIO. In case of MPAM-Fb, we use a > mutex, but only if we are in a sleepable context. If that's not the > case, we return an error. This should not happen, as MPAM-Fb by design > does not require an MSC access to happen from a specific CPU, so there > is no need for any IPIs or preemption disabling to satisfy CPU > constraints. And since overflow interrupts are not supported at the moment > anyway, we also wouldn't meet the other case. > Bailing out early is already happening in rare occasions today. > > Signed-off-by: Andre Przywara > Reviewed-by: Jonathan Cameron > --- > drivers/resctrl/mpam_devices.c | 6 +++++- > drivers/resctrl/mpam_internal.h | 38 +++++++++++++++++++++++++++------ > 2 files changed, 36 insertions(+), 8 deletions(-) > Reviewed-by: Gavin Shan