Ping: [PATCH v2 1/2] x86/PoD: correctly handle non-order-0 decrease-reservation requests

["Jan Beulich" <JBeulich@suse.com>]

>>> On 20.12.17 at 10:34, <JBeulich@suse.com> wrote:
> p2m_pod_decrease_reservation() at the moment only returns a boolean
> value: true for "nothing more to do", false for "something more to do".
> If it returns false, decrease_reservation() will loop over the entire
> range, calling guest_remove_page() for each page.
> 
> Unfortunately, in the case p2m_pod_decrease_reservation() succeeds
> partially, some of the memory in the range will be not-present; at which
> point guest_remove_page() will return an error, and the entire operation
> will fail.
> 
> Fix this by:
> 1. Having p2m_pod_decrease_reservation() return exactly the number of
>    gpfn pages it has handled (i.e., replaced with 'not present').
> 2. Making guest_remove_page() return -ENOENT in the case that the gpfn
>    in question was already empty (and in no other cases).
> 3. When looping over guest_remove_page(), expect the number of -ENOENT
>    failures to be no larger than the number of pages
>    p2m_pod_decrease_reservation() removed.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Signed-off-by: George Dunlap <george.dunlap@citrix.com>
> ---
> v2: Re-written description (by George). Add comments (as suggested
>     by George). Formatting.
> 
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -388,10 +388,10 @@ int guest_physmap_mark_populate_on_deman
>      return -ENOSYS;
>  }
>  
> -int p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn,
> -                                 unsigned int order)
> +unsigned long p2m_pod_decrease_reservation(struct domain *d, gfn_t gfn,
> +                                           unsigned int order)
>  {
> -    return -ENOSYS;
> +    return 0;
>  }
>  
>  static void p2m_set_permission(lpae_t *e, p2m_type_t t, p2m_access_t a)

Stefano, Julien?

Jan


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