[Xen-devel] Re: [PATCH] xen-gntdev: Fix unmap notify on PV domains

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Feb 08, 2011 at 09:14:06AM -0500, Daniel De Graaf wrote:
> In paravirtualized guests, the struct page* for mappings is only a
> placeholder, and cannot be used to access the granted memory. Use the
> userspace mapping that we have set up in order to implement
> UNMAP_NOTIFY_CLEAR_BYTE.
>     
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 06de2c0..2b67f15 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -287,7 +287,12 @@ static int unmap_grant_pages(struct grant_map *map, int 
> offset, int pages)
>  
>       if (map->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
>               int pgno = (map->notify.addr >> PAGE_SHIFT);
> -             if (pgno >= offset && pgno < offset + pages) {
> +             if (pgno >= offset && pgno < offset + pages && use_ptemod) {
> +                     void __user *tmp;
> +                     tmp = map->vma->vm_start + map->notify.addr;
> +                     copy_to_user(tmp, &err, 1);

The compiler really hates that. You could use a uninitialized_value macro
to ignore it.

> +                     map->notify.flags &= ~UNMAP_NOTIFY_CLEAR_BYTE;
> +             } else if (pgno >= offset && pgno < offset + pages) {
>                       uint8_t *tmp = kmap(map->pages[pgno]);
>                       tmp[map->notify.addr & (PAGE_SIZE-1)] = 0;
>                       kunmap(map->pages[pgno]);
> @@ -296,7 +301,7 @@ static int unmap_grant_pages(struct grant_map *map, int 
> offset, int pages)
>       }
>  
>       pr_debug("map %d+%d [%d+%d]\n", map->index, map->count, offset, pages);
> -     err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages, pages);
> +     err = gnttab_unmap_refs(map->unmap_ops + offset, map->pages + offset, 
> pages);
>       if (err)
>               return err;
>  

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