Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()

[Ira Weiny]

On Sun, Aug 11, 2019 at 06:50:44PM -0700, john.hubbard@xxxxxxxxx wrote:
> From: John Hubbard <jhubbard@xxxxxxxxxx>
> 
> This is the "vaddr_pin_pages" corresponding variant to
> get_user_pages_remote(), but with FOLL_PIN semantics: the implementation
> sets FOLL_PIN. That, in turn, means that the pages must ultimately be
> released by put_user_page*()--typically, via vaddr_unpin_pages*().
> 
> Note that the put_user_page*() requirement won't be truly
> required until all of the call sites have been converted, and
> the tracking of pages is actually activated.
> 
> Also introduce vaddr_unpin_pages(), in order to have a simpler
> call for the error handling cases.
> 
> Use both of these new calls in the Infiniband drive, replacing
> get_user_pages_remote() and put_user_pages().
> 
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> ---
>  drivers/infiniband/core/umem_odp.c | 15 +++++----
>  include/linux/mm.h                 |  7 +++++
>  mm/gup.c                           | 50 ++++++++++++++++++++++++++++++
>  3 files changed, 66 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
> index 53085896d718..fdff034a8a30 100644
> --- a/drivers/infiniband/core/umem_odp.c
> +++ b/drivers/infiniband/core/umem_odp.c
> @@ -534,7 +534,7 @@ static int ib_umem_odp_map_dma_single_page(
>  	}
>  
>  out:
> -	put_user_page(page);
> +	vaddr_unpin_pages(&page, 1, &umem_odp->umem.vaddr_pin);
>  
>  	if (remove_existing_mapping) {
>  		ib_umem_notifier_start_account(umem_odp);
> @@ -635,9 +635,10 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
>  		 * complex (and doesn't gain us much performance in most use
>  		 * cases).
>  		 */
> -		npages = get_user_pages_remote(owning_process, owning_mm,
> +		npages = vaddr_pin_pages_remote(owning_process, owning_mm,
>  				user_virt, gup_num_pages,
> -				flags, local_page_list, NULL, NULL);
> +				flags, local_page_list, NULL, NULL,
> +				&umem_odp->umem.vaddr_pin);

Thinking about this part of the patch... is this pin really necessary?  This
code is not doing a long term pin.  The page just needs a reference while we
map it into the devices page tables.  Once that is done we should get notifiers
if anything changes and we can adjust.  right?

Ira

>  		up_read(&owning_mm->mmap_sem);
>  
>  		if (npages < 0) {
> @@ -657,7 +658,8 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
>  					ret = -EFAULT;
>  					break;
>  				}
> -				put_user_page(local_page_list[j]);
> +				vaddr_unpin_pages(&local_page_list[j], 1,
> +						  &umem_odp->umem.vaddr_pin);
>  				continue;
>  			}
>  
> @@ -684,8 +686,9 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
>  			 * ib_umem_odp_map_dma_single_page().
>  			 */
>  			if (npages - (j + 1) > 0)
> -				put_user_pages(&local_page_list[j+1],
> -					       npages - (j + 1));
> +				vaddr_unpin_pages(&local_page_list[j+1],
> +						  npages - (j + 1),
> +						  &umem_odp->umem.vaddr_pin);
>  			break;
>  		}
>  	}
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 61b616cd9243..2bd76ad8787e 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1606,6 +1606,13 @@ int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
>  long vaddr_pin_pages(unsigned long addr, unsigned long nr_pages,
>  		     unsigned int gup_flags, struct page **pages,
>  		     struct vaddr_pin *vaddr_pin);
> +long vaddr_pin_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
> +			    unsigned long start, unsigned long nr_pages,
> +			    unsigned int gup_flags, struct page **pages,
> +			    struct vm_area_struct **vmas, int *locked,
> +			    struct vaddr_pin *vaddr_pin);
> +void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
> +		       struct vaddr_pin *vaddr_pin);
>  void vaddr_unpin_pages_dirty_lock(struct page **pages, unsigned long nr_pages,
>  				  struct vaddr_pin *vaddr_pin, bool make_dirty);
>  bool mapping_inode_has_layout(struct vaddr_pin *vaddr_pin, struct page *page);
> diff --git a/mm/gup.c b/mm/gup.c
> index 85f09958fbdc..bb95adfaf9b6 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2518,6 +2518,38 @@ long vaddr_pin_pages(unsigned long addr, unsigned long nr_pages,
>  }
>  EXPORT_SYMBOL(vaddr_pin_pages);
>  
> +/**
> + * vaddr_pin_pages pin pages by virtual address and return the pages to the
> + * user.
> + *
> + * @tsk:	the task_struct to use for page fault accounting, or
> + *		NULL if faults are not to be recorded.
> + * @mm:		mm_struct of target mm
> + * @addr:	start address
> + * @nr_pages:	number of pages to pin
> + * @gup_flags:	flags to use for the pin
> + * @pages:	array of pages returned
> + * @vaddr_pin:	initialized meta information this pin is to be associated
> + * with.
> + *
> + * This is the "vaddr_pin_pages" corresponding variant to
> + * get_user_pages_remote(), but with FOLL_PIN semantics: the implementation sets
> + * FOLL_PIN. That, in turn, means that the pages must ultimately be released
> + * by put_user_page().
> + */
> +long vaddr_pin_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
> +			    unsigned long start, unsigned long nr_pages,
> +			    unsigned int gup_flags, struct page **pages,
> +			    struct vm_area_struct **vmas, int *locked,
> +			    struct vaddr_pin *vaddr_pin)
> +{
> +	gup_flags |= FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN;
> +
> +	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
> +				       locked, gup_flags, vaddr_pin);
> +}
> +EXPORT_SYMBOL(vaddr_pin_pages_remote);
> +
>  /**
>   * vaddr_unpin_pages_dirty_lock - counterpart to vaddr_pin_pages
>   *
> @@ -2536,3 +2568,21 @@ void vaddr_unpin_pages_dirty_lock(struct page **pages, unsigned long nr_pages,
>  	__put_user_pages_dirty_lock(vaddr_pin, pages, nr_pages, make_dirty);
>  }
>  EXPORT_SYMBOL(vaddr_unpin_pages_dirty_lock);
> +
> +/**
> + * vaddr_unpin_pages - simple, non-dirtying counterpart to vaddr_pin_pages
> + *
> + * @pages: array of pages returned
> + * @nr_pages: number of pages in pages
> + * @vaddr_pin: same information passed to vaddr_pin_pages
> + *
> + * Like vaddr_unpin_pages_dirty_lock, but for non-dirty pages. Useful in putting
> + * back pages in an error case: they were never made dirty.
> + */
> +void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
> +		       struct vaddr_pin *vaddr_pin)
> +{
> +	__put_user_pages_dirty_lock(vaddr_pin, pages, nr_pages, false);
> +}
> +EXPORT_SYMBOL(vaddr_unpin_pages);
> +
> -- 
> 2.22.0
>