Re: [PATCH v6 17/17] RFC: mm: add mmu_notifier argument to follow_pfn

[Jason Gunthorpe]

On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote:
> @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd);
>   * Return: zero and the pfn at @pfn on success, -ve otherwise.
>   */
>  int follow_pfn(struct vm_area_struct *vma, unsigned long address,
> -	unsigned long *pfn)
> +	unsigned long *pfn, struct mmu_notifier *subscription)
>  {
> -	int ret = -EINVAL;
> -	spinlock_t *ptl;
> -	pte_t *ptep;
> +	if (WARN_ON(!subscription->mm))
> +		return -EINVAL;
>  
> +	if (WARN_ON(subscription->mm != vma->vm_mm))
> +		return -EINVAL;

These two things are redundant right? vma->vm_mm != NULL?

BTW, why do we even have this for nommu? If the only caller is kvm,
can you even compile kvm on nommu??

Jason