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[175.34.8.244]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c82bb07d2f2sm11414785a12.10.2026.05.17.21.28.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 17 May 2026 21:28:46 -0700 (PDT) Message-ID: <4c79ff7b-5176-4fd7-8427-0f7a1113f31b@redhat.com> Date: Mon, 18 May 2026 14:28:40 +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 v1] virt: arm-cca-guest: use raw variant of smp_processor_id() in arm_cca_report_new() To: Kohei Enju , Catalin Marinas , Will Deacon Cc: Sami Mujawar , Steven Price , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260518033157.1865498-1-enju.kohei@fujitsu.com> Content-Language: en-US From: Gavin Shan In-Reply-To: <20260518033157.1865498-1-enju.kohei@fujitsu.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/18/26 1:31 PM, Kohei Enju wrote: > With CONFIG_DEBUG_PREEMPT=y, smp_processor_id() becomes an alias of > debug_smp_processor_id(). This debug function complains when certain > conditions that ensure CPU ID stability are not met, specifically when > it's called from a preemptible context. > > In arm_cca_report_new(), which runs in a preemptible context, > smp_processor_id() triggers a splat [0] due to this. > > However, the CPU ID obtained here is used as the target CPU for > smp_call_function_single() to designate a specific CPU for subsequent > operations, not to assert that the current thread will continue to > execute on the same CPU. Therefore, snapshotting the CPU ID itself is > correct, and thus there's no actual harm except for the splat. > > Use raw_smp_processor_id() instead, to directly retrieve the current CPU > ID without the debug checks, avoiding the unnecessary warning message > while preserving the correct functional behavior. > > [0] > BUG: using smp_processor_id() in preemptible [00000000] code: cca-workload-at/134 > caller is debug_smp_processor_id+0x20/0x2c > CPU: 0 UID: 0 PID: 134 Comm: cca-workload-at Not tainted 7.0.0-rc1-gc74a64d12073 #1 PREEMPT > Hardware name: linux,dummy-virt (DT) > Call trace: > [...] > check_preemption_disabled+0xf8/0x100 > debug_smp_processor_id+0x20/0x2c > arm_cca_report_new+0x54/0x230 > tsm_report_read+0x184/0x260 > tsm_report_outblob_read+0x18/0x38 > configfs_bin_read_iter+0xf4/0x1dc > vfs_read+0x230/0x31c > [...] > > Fixes: 7999edc484ca ("virt: arm-cca-guest: TSM_REPORT support for realms") > Signed-off-by: Kohei Enju > --- > drivers/virt/coco/arm-cca-guest/arm-cca-guest.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > Reviewed-by: Gavin Shan