Re: [PATCH 4/6] xen-gntdev: Support mapping in HVM domains

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Feb 14, 2011 at 12:43:10PM -0500, Daniel De Graaf wrote:
> On 02/14/2011 10:51 AM, Konrad Rzeszutek Wilk wrote:
> >> +static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
> >> +
> >>  /* ------------------------------------------------------------------ */
> >>  
> >>  static void gntdev_print_maps(struct gntdev_priv *priv,
> >> @@ -179,11 +184,34 @@ static void gntdev_put_map(struct grant_map *map)
> >>  
> >>  	atomic_sub(map->count, &pages_mapped);
> >>  
> >> -	if (map->pages)
> >> +	if (map->pages) {
> >> +		if (!use_ptemod)
> >> +			unmap_grant_pages(map, 0, map->count);
> > 
> > In the past (before this patch) the unmap_grant_pages would be called
> > on the .ioctl, .release, and .close (on VMA). This adds it now also
> > on the mmu_notifier_ops paths. Why?
> > 
> This does not actually add the unmap on the mmu_notifier path. The MMU

Duh, you are right. I misread my notes. I meant that in the past the
.ioctl, .release, and .close would just do gntdev_put_map, but now they
are also calling the unmap_grant_pages (on the HVM path).

> notifier is used only if use_ptemod is true, and unmap_grant_pages is
> only called when use_ptemod is false.

.. and that would explain it - you need to call it on, and the MMU notifier
is unavailable for you on HVM case.

Not exactly sure why that wasn't clear before.

> 
> The HVM path for map and unmap is slightly different: HVM keeps the pages
> mapped until the area is deleted, while the PV case (use_ptemod being true)
> must unmap them when userspace unmaps the range. In the normal use case,
> this makes no difference to users since unmap time is deletion time.

<nods> Let me augment the path description to contain this.

> 
> -- 
> Daniel De Graaf
> National Security Agency