Re: [PATCH v3] virt: arm-cca-guest: use migrate_disable() for attestation token requests

[Gavin Shan <gshan@redhat.com>]

On 6/12/26 9:09 PM, Kohei Enju wrote:
> The RSI attestation token init and continue calls must be issued from
> the same CPU. arm_cca_report_new() currently snapshots the CPU number
> and uses smp_call_function_single() to issue those calls on that CPU.
> 
> With CONFIG_DEBUG_PREEMPT=y, the smp_processor_id() call used for the
> snapshot triggers a debug splat [0] because it runs in preemptible
> context. The snapshot does not pin the task to that CPU; it is only used
> to choose the target CPU for smp_call_function_single(), which can fail
> if that CPU is no longer available.
> 
> Use migrate_disable() and issue the token init and continue operations
> directly, without the smp_call_function_single() callbacks. This keeps
> the token request sequence on the same CPU while preserving a sleepable
> context for the GFP_KERNEL allocations needed after the init call.
> 
> [0]
>   BUG: using smp_processor_id() in preemptible [00000000] code: cca-workload-at/264
>   caller is debug_smp_processor_id+0x20/0x30
>   CPU: 0 UID: 0 PID: 264 Comm: cca-workload-at Not tainted 7.1.0-rc1-00044-g55542ab273f2 #80 PREEMPT(lazy)
>   Hardware name: linux,dummy-virt (DT)
>   Call trace:
>    [...]
>    check_preemption_disabled+0xd8/0xf8
>    debug_smp_processor_id+0x20/0x30
>    arm_cca_report_new+0x48/0x278
>    tsm_report_read+0x154/0x1f8
>    tsm_report_outblob_read+0x20/0x38
>    configfs_bin_read_iter+0x118/0x208
>    vfs_read+0x220/0x318
>    [...]
> 
> Fixes: 7999edc484ca ("virt: arm-cca-guest: TSM_REPORT support for realms")
> Signed-off-by: Kohei Enju <enju.kohei@fujitsu.com>
> ---
> Changes:
> v3:
>    - Switch to migrate_disable() and call RSI directly, removing
>      smp_call_function_single() (Will, Suzuki)
>    - Remove arm_cca_attestation_init() helper and unused fields from
>      arm_cca_token_info
>    - Drop Reviewed-by tags since the approach changed from v2
> v2: https://lore.kernel.org/linux-arm-kernel/20260519101217.155740-1-enju.kohei@fujitsu.com/
>    - Add comment about why this path doesn't use migrate_disable()
> v1: https://lore.kernel.org/linux-arm-kernel/20260518033157.1865498-1-enju.kohei@fujitsu.com/
> ---
>   .../virt/coco/arm-cca-guest/arm-cca-guest.c   | 97 +++++++------------
>   1 file changed, 36 insertions(+), 61 deletions(-)
> 
Reviewed-by: Gavin Shan <gshan@redhat.com>