Re: [Xen-devel] [PATCH 3/4] xen/arm: create_p2m_entries should not call free_domheap_page

[Tim Deegan <tim@xxxxxxx>]

At 12:05 +0100 on 04 Jul (1341403533), Stefano Stabellini wrote:
> The guest is entitled to use valid memory pages as pfns for grant_table
> usage.
> 
> In these cases we shouldn't call free_domheap_page to free the existing
> page from create_p2m_entries, because it resets the reference counting
> but the page is still allocated to the guest (even if not in the p2m
> anymore) and common grant_table code is also going to call put_page on
> it.

Does this break other users?  I guess this answers my earlier question
about needing refcounts, anyway -- we'll need to use them everywhere
to keep the grant-table code consistent.

Cheers,

Tim.

> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> ---
>  xen/arch/arm/p2m.c |    5 -----
>  1 files changed, 0 insertions(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 7c23b7d..7ae4515 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -189,12 +189,7 @@ static int create_p2m_entries(struct domain *d,
>          /* else: third already valid */
>  
>          if ( third[third_table_offset(addr)].p2m.valid )
> -        {
> -            /* p2m entry already present */
> -            free_domheap_page(
> -                    mfn_to_page(third[third_table_offset(addr)].p2m.base));
>              flush_tlb_all_local();
> -        }
>  
>          /* Allocate a new RAM page and attach */
>          switch (op) {
> -- 
> 1.7.2.5
> 
> 
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