From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v6] x86/p2m: use large pages for MMIO
	mappings
Date: Mon, 1 Feb 2016 15:00:04 +0000
Message-ID: <56AF72F4.7020708@citrix.com>
References: <56AF301402000078000CCC63@prv-mh.provo.novell.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta14.messagelabs.com ([193.109.254.103])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <prvs=832ee56b7=Andrew.Cooper3@citrix.com>)
	id 1aQFxZ-0000Cb-9F
	for xen-devel@lists.xenproject.org; Mon, 01 Feb 2016 15:00:09 +0000
In-Reply-To: <56AF301402000078000CCC63@prv-mh.provo.novell.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xenproject.org>
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, George Dunlap <George.Dunlap@eu.citrix.com>, Tim Deegan <tim@xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Jun Nakajima <jun.nakajima@intel.com>, Keir Fraser <keir@xen.org>
List-Id: xen-devel@lists.xenproject.org

On 01/02/16 09:14, Jan Beulich wrote:
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -899,48 +899,64 @@ void p2m_change_type_range(struct domain
>      p2m_unlock(p2m);
>  }
>  
> -/* Returns: 0 for success, -errno for failure */
> +/*
> + * Returns:
> + *    0              for success
> + *    -errno         for failure
> + *    1 + new order  for caller to retry with smaller order (guaranteed
> + *                   to be smaller than order passed in)
> + */
>  static int set_typed_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn,
> -                               p2m_type_t gfn_p2mt, p2m_access_t access)
> +                               unsigned int order, p2m_type_t gfn_p2mt,
> +                               p2m_access_t access)
>  {
>      int rc = 0;
>      p2m_access_t a;
>      p2m_type_t ot;
>      mfn_t omfn;
> +    unsigned int cur_order = 0;
>      struct p2m_domain *p2m = p2m_get_hostp2m(d);
>  
>      if ( !paging_mode_translate(d) )
>          return -EIO;
>  
> -    gfn_lock(p2m, gfn, 0);
> -    omfn = p2m->get_entry(p2m, gfn, &ot, &a, 0, NULL, NULL);
> +    gfn_lock(p2m, gfn, order);
> +    omfn = p2m->get_entry(p2m, gfn, &ot, &a, 0, &cur_order, NULL);
> +    if ( cur_order < order )
> +    {
> +        gfn_unlock(p2m, gfn, order);
> +        return cur_order + 1;
> +    }
>      if ( p2m_is_grant(ot) || p2m_is_foreign(ot) )
>      {
> -        gfn_unlock(p2m, gfn, 0);
> +        gfn_unlock(p2m, gfn, order);
>          domain_crash(d);
>          return -ENOENT;
>      }
>      else if ( p2m_is_ram(ot) )
>      {
> -        ASSERT(mfn_valid(omfn));
> -        set_gpfn_from_mfn(mfn_x(omfn), INVALID_M2P_ENTRY);
> +        unsigned long i;
> +
> +        for ( i = 0; i < (1UL << order); ++i )
> +        {
> +            ASSERT(mfn_valid(_mfn(mfn_x(omfn) + i)));
> +            set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);

On further consideration, shouldn't we have a preemption check here? 
Removing a 1GB superpage's worth of RAM mappings is going to execute for
an unreasonably long time.

~Andrew