Re: [PATCH RFC V2 12/17] memremap: Add zone device access protection

[Peter Zijlstra]

On Fri, Jul 17, 2020 at 12:20:51AM -0700, ira.we...@intel.com wrote:
> +void dev_access_disable(void)
> +{
> +     unsigned long flags;
> +
> +     if (!static_branch_unlikely(&dev_protection_static_key))
> +             return;
> +
> +     local_irq_save(flags);
> +     current->dev_page_access_ref--;
> +     if (current->dev_page_access_ref == 0)

        if (!--current->dev_page_access_ref)

> +             pks_update_protection(dev_page_pkey, PKEY_DISABLE_ACCESS);
> +     local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(dev_access_disable);
> +
> +void dev_access_enable(void)
> +{
> +     unsigned long flags;
> +
> +     if (!static_branch_unlikely(&dev_protection_static_key))
> +             return;
> +
> +     local_irq_save(flags);
> +     /* 0 clears the PKEY_DISABLE_ACCESS bit, allowing access */
> +     if (current->dev_page_access_ref == 0)
> +             pks_update_protection(dev_page_pkey, 0);
> +     current->dev_page_access_ref++;

        if (!current->dev_page_access_ref++)

> +     local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(dev_access_enable);


Also, you probably want something like:

static __always_inline devm_access_disable(void)
{
        if (static_branch_unlikely(&dev_protection_static_key))
                __devm_access_disable();
}

static __always_inline devm_access_enable(void)
{
        if (static_branch_unlikely(&dev_protection_static_key))
                __devm_access_enable();
}