From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: [PATCH v4 3/3] xen/arm: introduce
	XENFEAT_grant_map_identity
Date: Mon, 28 Jul 2014 13:05:47 +0100
Message-ID: <53D63C9B.5090300@linaro.org>
References: <alpine.DEB.2.02.1407281111250.2293@kaball.uk.xensource.com>
	<1406542610-18724-3-git-send-email-stefano.stabellini@eu.citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
In-Reply-To: <1406542610-18724-3-git-send-email-stefano.stabellini@eu.citrix.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: Stefano Stabellini <stefano.stabellini@eu.citrix.com>, xen-devel@lists.xensource.com
Cc: julien.grall@citrix.com, Ian.Campbell@citrix.com
List-Id: xen-devel@lists.xenproject.org

Hi Stefano,

On 07/28/2014 11:16 AM, Stefano Stabellini wrote:
> The flag specifies that the hypervisor maps a grant page to guest
> physical address == machine address of the page in addition to the
> normal grant mapping address.
> 
> Frontends are allowed to map the same page multiple times using multiple
> grant references. On the backend side it can be difficult to find out
> the physical address corresponding to a particular machine address,
> especially at the completation of a dma operation. To simplify address

completion

[..]

>          if ( err )
>          {
> @@ -941,9 +951,18 @@ __gnttab_unmap_common(
>          int err = 0;
>          mapcount(lgt, rd, op->frame, &wrc, &rdc);
>          if ( (wrc + rdc) == 0 )
> -            err = iommu_unmap_page(ld, op->frame);
> -        else if ( wrc == 0 )
> -            err = iommu_map_page(ld, op->frame, op->frame, IOMMUF_readable);
> +        {
> +            if ( is_domain_direct_mapped(ld) )
> +                err = arch_grant_unmap_page_identity(ld, op->frame);
> +            else
> +                err = iommu_unmap_page(ld, op->frame);
> +        } else if ( wrc == 0 )
> +        {
> +            if ( is_domain_direct_mapped(ld) )
> +                err = arch_grant_map_page_identity(ld, op->frame, 0);
> +            else
> +                err = iommu_map_page(ld, op->frame, op->frame, IOMMUF_readable);

With this solution, iommu_map_page will never be called on ARM. It's
because gnttab_need_iommu_mapping is checking the domain is using direct
mapping.

So, I think you can drop the iommu_map_page callback of the SMMU in
patch #2.

Regards,

-- 
Julien Grall