Re: [PATCH v1] virt: arm-cca-guest: use raw variant of smp_processor_id() in arm_cca_report_new()

[Gavin Shan]

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 <enju.kohei@xxxxxxxxxxx>
> ---
>   drivers/virt/coco/arm-cca-guest/arm-cca-guest.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>