[PATCH v3 hmm 02/12] mm/hmm: Use hmm_mirror not mm as an argument for hmm_range_register

[Christoph Hellwig]

On Thu, Jun 13, 2019 at 09:44:40PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg at mellanox.com>
> 
> Ralph observes that hmm_range_register() can only be called by a driver
> while a mirror is registered. Make this clear in the API by passing in the
> mirror structure as a parameter.
> 
> This also simplifies understanding the lifetime model for struct hmm, as
> the hmm pointer must be valid as part of a registered mirror so all we
> need in hmm_register_range() is a simple kref_get.

Looks good, at least an an intermediate step:

Reviewed-by: Christoph Hellwig <hch at lst.de>

> index f6956d78e3cb25..22a97ada108b4e 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -914,13 +914,13 @@ static void hmm_pfns_clear(struct hmm_range *range,
>   * Track updates to the CPU page table see include/linux/hmm.h
>   */
>  int hmm_range_register(struct hmm_range *range,
> -		       struct mm_struct *mm,
> +		       struct hmm_mirror *mirror,
>  		       unsigned long start,
>  		       unsigned long end,
>  		       unsigned page_shift)
>  {
>  	unsigned long mask = ((1UL << page_shift) - 1UL);
> -	struct hmm *hmm;
> +	struct hmm *hmm = mirror->hmm;
>  
>  	range->valid = false;
>  	range->hmm = NULL;
> @@ -934,20 +934,15 @@ int hmm_range_register(struct hmm_range *range,
>  	range->start = start;
>  	range->end = end;

But while you're at it:  the calling conventions of hmm_range_register
are still rather odd, as the staet, end and page_shift arguments are
only used to fill out fields in the range structure passed in.  Might
be worth cleaning up as well if we change the calling convention.