Re: [RFCv2 03/10] x86: Introduce userspace API to handle per-thread features

Thomas Gleixner
2022-05-12T12:02:57Z

On Wed, May 11 2022 at 05:27, Kirill A. Shutemov wrote:
> Add three new arch_prctl() handles:
>
> +static long thread_feature_prctl(struct task_struct *task, int option,
> + unsigned long features)

Bah. I really hate the task pointer on all these x86 prctls. @task must
always be current, so this @task argument is just confusion.

> +{
> + const unsigned long known_features = 0;
> +
> + if (features & ~known_features)
> + return -EINVAL;

This implementation allows to task->read features_[locked] with
@features == 0. That should be documented somewhere.

> + if (option == ARCH_THREAD_FEATURE_LOCK) {
> + task->thread.features_locked |= features;
> + return task->thread.features_locked;
> + }

> + /* Do not allow to change locked features */
> + if (features & task->thread.features_locked)
> + return -EPERM;
> +
> + if (option == ARCH_THREAD_FEATURE_DISABLE) {
> + task->thread.features &= ~features;
> + goto out;
> + }
> +
> + /* Handle ARCH_THREAD_FEATURE_ENABLE */
> +
> + task->thread.features |= features;
> +out:
> + return task->thread.features;

Eyes bleed.

if (option == ARCH_THREAD_FEATURE_ENABLE)
task->thread.features |= features;
else
task->thread.features &= ~features;

return task->thread.features;

It's bloody obvious from the code that the counterpart of enable is
disable, no? So neither the goto nor the 'comment the obvious' is useful
in any way.

Thanks,

tglx