Re: [PATCH 08/19] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote()

Ira Weiny
2019-10-31T23:35:26Z

On Wed, Oct 30, 2019 at 03:49:19PM -0700, John Hubbard wrote:
> Convert process_vm_access to use the new pin_user_pages_remote()
> call, which sets FOLL_PIN. Setting FOLL_PIN is now required for
> code that requires tracking of pinned pages.
>
> Also, release the pages via put_user_page*().
>
> Also, rename "pages" to "pinned_pages", as this makes for
> easier reading of process_vm_rw_single_vec().

Ok... but it made review a bit harder...

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> mm/process_vm_access.c | 28 +++++++++++++++-------------
> 1 file changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
> index 357aa7bef6c0..fd20ab675b85 100644
> --- a/mm/process_vm_access.c
> +++ b/mm/process_vm_access.c
> @@ -42,12 +42,11 @@ static int process_vm_rw_pages(struct page **pages,
> if (copy > len)
> copy = len;
>
> - if (vm_write) {
> + if (vm_write)
> copied = copy_page_from_iter(page, offset, copy, iter);
> - set_page_dirty_lock(page);
> - } else {
> + else
> copied = copy_page_to_iter(page, offset, copy, iter);
> - }
> +
> len -= copied;
> if (copied < copy && iov_iter_count(iter))
> return -EFAULT;
> @@ -96,7 +95,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
> flags |= FOLL_WRITE;
>
> while (!rc && nr_pages && iov_iter_count(iter)) {
> - int pages = min(nr_pages, max_pages_per_loop);
> + int pinned_pages = min(nr_pages, max_pages_per_loop);
> int locked = 1;
> size_t bytes;
>
> @@ -106,14 +105,15 @@ static int process_vm_rw_single_vec(unsigned long addr,
> * current/current->mm
> */
> down_read(&mm->mmap_sem);
> - pages = get_user_pages_remote(task, mm, pa, pages, flags,
> - process_pages, NULL, &locked);
> + pinned_pages = pin_user_pages_remote(task, mm, pa, pinned_pages,
> + flags, process_pages,
> + NULL, &locked);
> if (locked)
> up_read(&mm->mmap_sem);
> - if (pages <= 0)
> + if (pinned_pages <= 0)
> return -EFAULT;
>
> - bytes = pages * PAGE_SIZE - start_offset;
> + bytes = pinned_pages * PAGE_SIZE - start_offset;
> if (bytes > len)
> bytes = len;
>
> @@ -122,10 +122,12 @@ static int process_vm_rw_single_vec(unsigned long addr,
> vm_write);
> len -= bytes;
> start_offset = 0;
> - nr_pages -= pages;
> - pa += pages * PAGE_SIZE;
> - while (pages)
> - put_page(process_pages[--pages]);
> + nr_pages -= pinned_pages;
> + pa += pinned_pages * PAGE_SIZE;
> +
> + /* If vm_write is set, the pages need to be made dirty: */
> + put_user_pages_dirty_lock(process_pages, pinned_pages,
> + vm_write);
> }
>
> return rc;
> --
> 2.23.0
>