From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [PATCH 2/4] xen: introduce grant_map_exists
Date: Thu, 02 Oct 2014 11:45:14 +0100
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References: <alpine.DEB.2.02.1410021029170.17038@kaball.uk.xensource.com>
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: julien.grall@citrix.com, xen-devel <xen-devel@lists.xenproject.org>, tim@xen.org, Ian.Campbell@citrix.com
List-Id: xen-devel@lists.xenproject.org

>>> On 02.10.14 at 12:02, <stefano.stabellini@eu.citrix.com> wrote:
> --- a/xen/common/grant_table.c
> +++ b/xen/common/grant_table.c
> @@ -484,6 +484,38 @@ static int _set_status(unsigned gt_version,
>          return _set_status_v2(domid, readonly, mapflag, shah, act, status);
>  }
>  
> +bool_t grant_map_exists(struct domain *ld,
> +                        struct grant_table *rgt,
> +                        unsigned long mfn)
> +{
> +    struct active_grant_entry *act;
> +    grant_ref_t ref;
> +    bool_t ret = 0;
> +
> +    spin_lock(&rgt->lock);
> +
> +    for ( ref = 0; ref != nr_grant_entries(rgt); ref++ )
> +    {
> +        act = &active_entry(rgt, ref);
> +
> +        if ( !act->pin )
> +            continue;
> +
> +        if ( act->domid != ld->domain_id )
> +            continue;
> +
> +        if ( act->frame != mfn )
> +            continue;
> +        
> +        ret = 1;
> +        break;
> +    }
> +
> +    spin_unlock(&rgt->lock);
> +
> +    return ret;

By the time you get here the information you return is stale. Is that
not a problem for the caller? And if it's not, why would it check in the
first place?

Jan