Re: [Xen-devel] [PATCHv4 11/14] xen/gntdev: safely unmap grants in case they are still in use

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 26 Jan 2015, David Vrabel wrote:
> From: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>
> 
> Use gnttab_unmap_refs_async() to wait until the mapped pages are no
> longer in use before unmapping them.
> 
> This allows userspace programs to safely use Direct I/O and AIO to a
> network filesystem which may retain refs to pages in queued skbs after
> the filesystem I/O has completed.
> 
> Signed-off-by: Jennifer Herbert <jennifer.herbert@xxxxxxxxxx>
> Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>

Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


>  drivers/xen/gntdev.c |   36 +++++++++++++++++++++++++++++++-----
>  1 file changed, 31 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index c1a03fa..494bd06 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -311,9 +311,30 @@ static int map_grant_pages(struct grant_map *map)
>       return err;
>  }
>  
> +struct unmap_grant_pages_callback_data
> +{
> +     struct completion completion;
> +     int result;
> +};
> +
> +static void unmap_grant_callback(int result,
> +                              struct gntab_unmap_queue_data *data)
> +{
> +     struct unmap_grant_pages_callback_data* d = data->data;
> +
> +     d->result = result;
> +     complete(&d->completion);
> +}
> +
>  static int __unmap_grant_pages(struct grant_map *map, int offset, int pages)
>  {
>       int i, err = 0;
> +     struct gntab_unmap_queue_data unmap_data;
> +     struct unmap_grant_pages_callback_data data;
> +
> +     init_completion(&data.completion);
> +     unmap_data.data = &data;
> +     unmap_data.done= &unmap_grant_callback;
>  
>       if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
>               int pgno = (map->notify.addr >> PAGE_SHIFT);
> @@ -325,11 +346,16 @@ static int __unmap_grant_pages(struct grant_map *map, 
> int offset, int pages)
>               }
>       }
>  
> -     err = gnttab_unmap_refs(map->unmap_ops + offset,
> -                     use_ptemod ? map->kunmap_ops + offset : NULL, 
> map->pages + offset,
> -                     pages);
> -     if (err)
> -             return err;
> +     unmap_data.unmap_ops = map->unmap_ops + offset;
> +     unmap_data.kunmap_ops = use_ptemod ? map->kunmap_ops + offset : NULL;
> +     unmap_data.pages = map->pages + offset;
> +     unmap_data.count = pages;
> +
> +     gnttab_unmap_refs_async(&unmap_data);
> +
> +     wait_for_completion(&data.completion);
> +     if (data.result)
> +             return data.result;
>  
>       for (i = 0; i < pages; i++) {
>               if (map->unmap_ops[offset+i].status)
> -- 
> 1.7.10.4
> 
> 
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> 

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