Re: [Xen-devel] mem_sharing_nominate_page: p2mt should never change before p2m_change_type()

[Andres Lagar-Cavilla <andreslc@xxxxxxxxxxxxxx>]

> The p2mt change check for p2m_change_type() was first introduced when this 
> code path was not protected by p2m_lock().
> Now this code path is protected by p2m_lock. So p2mt should never change 
> before p2m_change_type().

Makes sense. You need to put a proper Signed-off-by line. In any case:
Acked-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

Andres
> 
> ---
> diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
> index 0364bb0..b3940cb 100644
> --- a/xen/arch/x86/mm/mem_sharing.c
> +++ b/xen/arch/x86/mm/mem_sharing.c
> @@ -900,20 +900,8 @@ int mem_sharing_nominate_page(struct domain *d,
>         goto out;
>     }
> 
> -    /* Change the p2m type */
> -    if ( p2m_change_type(d, gfn, p2mt, p2m_ram_shared) != p2mt )
> -    {
> -        /* This is unlikely, as the type must have changed since we've 
> checked
> -         * it a few lines above.
> -         * The mfn needs to revert back to rw type. This should never fail,
> -         * since no-one knew that the mfn was temporarily sharable */
> -        mem_sharing_gfn_destroy(page, d, gfn_info);
> -        xfree(page->sharing);
> -        page->sharing = NULL;
> -        /* NOTE: We haven't yet added this to the audit list. */
> -        BUG_ON(page_make_private(d, page) != 0);
> -        goto out;
> -    }
> +    /* Change the p2m type, should never fail with p2m locked. */
> +    BUG_ON(p2m_change_type(d, gfn, p2mt, p2m_ram_shared) != p2mt);
> 
>     /* Account for this page. */
>     atomic_inc(&nr_shared_mfns);
> 
> 
> 


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