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

Peter Zijlstra
2020-07-17T09:17:33Z

On Fri, Jul 17, 2020 at 12:20:51AM -0700, ira.weiny@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();
}