[Xen-devel] Re: [PATCH v2] xen/gntdev, gntalloc: Remove unneeded VM flags

Ian Campbell
Tue, 08 Mar 2011 09:54:00 -0000

On Mon, 2011-03-07 at 20:18 +0000, Daniel De Graaf
wrote:
> The only time when granted pages need to be treated specially is when
> using Xen''s PTE modification for grant mappings owned by another
domain
> (that is, only gntdev on PV guests).  Otherwise, the area does not
> require VM_DONTCOPY and VM_PFNMAP, since it can be accessed just like
> any other page of RAM.
>
> Since the vm_operations_struct close operations decrement reference
> counts, a corresponding open function that increments them is required
> now that it is possible to have multiple references to a single area.
>
> Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>

Looks good, thanks.

Acked-by: Ian Campbell <ian.campbell@citrix.com>

> ---
>  drivers/xen/gntalloc.c |   14 ++++++++++++--
>  drivers/xen/gntdev.c   |   16 ++++++++++++++--
>  2 files changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/xen/gntalloc.c b/drivers/xen/gntalloc.c
> index a7ffdfe..f6832f4 100644
> --- a/drivers/xen/gntalloc.c
> +++ b/drivers/xen/gntalloc.c
> @@ -427,6 +427,17 @@ static long gntalloc_ioctl(struct file *filp, unsigned
int cmd,
>  	return 0;
>  }
>
> +static void gntalloc_vma_open(struct vm_area_struct *vma)
> +{
> +	struct gntalloc_gref *gref = vma->vm_private_data;
> +	if (!gref)
> +		return;
> +
> +	spin_lock(&gref_lock);
> +	gref->users++;
> +	spin_unlock(&gref_lock);
> +}
> +
>  static void gntalloc_vma_close(struct vm_area_struct *vma)
>  {
>  	struct gntalloc_gref *gref = vma->vm_private_data;
> @@ -441,6 +452,7 @@ static void gntalloc_vma_close(struct vm_area_struct
*vma)
>  }
>
>  static struct vm_operations_struct gntalloc_vmops = {
> +	.open = gntalloc_vma_open,
>  	.close = gntalloc_vma_close,
>  };
>
> @@ -471,8 +483,6 @@ static int gntalloc_mmap(struct file *filp, struct
vm_area_struct *vma)
>  	vma->vm_private_data = gref;
>
>  	vma->vm_flags |= VM_RESERVED;
> -	vma->vm_flags |= VM_DONTCOPY;
> -	vma->vm_flags |= VM_PFNMAP | VM_PFN_AT_MMAP;
>
>  	vma->vm_ops = &gntalloc_vmops;
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 2faf797..69c787a 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -334,17 +334,26 @@ static int unmap_grant_pages(struct grant_map *map,
int offset, int pages)
>
>  /* ------------------------------------------------------------------ */
>
> +static void gntdev_vma_open(struct vm_area_struct *vma)
> +{
> +	struct grant_map *map = vma->vm_private_data;
> +
> +	pr_debug("gntdev_vma_open %p\n", vma);
> +	atomic_inc(&map->users);
> +}
> +
>  static void gntdev_vma_close(struct vm_area_struct *vma)
>  {
>  	struct grant_map *map = vma->vm_private_data;
>
> -	pr_debug("close %p\n", vma);
> +	pr_debug("gntdev_vma_close %p\n", vma);
>  	map->vma = NULL;
>  	vma->vm_private_data = NULL;
>  	gntdev_put_map(map);
>  }
>
>  static struct vm_operations_struct gntdev_vmops = {
> +	.open = gntdev_vma_open,
>  	.close = gntdev_vma_close,
>  };
>
> @@ -656,7 +665,10 @@ static int gntdev_mmap(struct file *flip, struct
vm_area_struct *vma)
>
>  	vma->vm_ops = &gntdev_vmops;
>
> -	vma->vm_flags |= VM_RESERVED|VM_DONTCOPY|VM_DONTEXPAND|VM_PFNMAP;
> +	vma->vm_flags |= VM_RESERVED|VM_DONTEXPAND;
> +
> +	if (use_ptemod)
> +		vma->vm_flags |= VM_DONTCOPY|VM_PFNMAP;
>
>  	vma->vm_private_data = map;