Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 6 Jul 2022 15:17:04 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Nicolin Chen <nicolinc@nvidia.com>
Cc:     kwankhede@nvidia.com, corbet@lwn.net, hca@linux.ibm.com,
        gor@linux.ibm.com, agordeev@linux.ibm.com,
        borntraeger@linux.ibm.com, svens@linux.ibm.com,
        zhenyuw@linux.intel.com, zhi.a.wang@intel.com,
        jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com,
        rodrigo.vivi@intel.com, tvrtko.ursulin@linux.intel.com,
        airlied@linux.ie, daniel@ffwll.ch, farman@linux.ibm.com,
        mjrosato@linux.ibm.com, pasic@linux.ibm.com, vneethv@linux.ibm.com,
        oberpar@linux.ibm.com, freude@linux.ibm.com,
        akrowiak@linux.ibm.com, jjherne@linux.ibm.com,
        alex.williamson@redhat.com, cohuck@redhat.com,
        kevin.tian@intel.com, hch@infradead.org, jchrist@linux.ibm.com,
        kvm@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
        intel-gvt-dev@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [RFT][PATCH v2 8/9] vfio/ccw: Add kmap_local_page() for memcpy
Message-ID: <20220706181704.GP693670@nvidia.com>
References: <20220706062759.24946-1-nicolinc@nvidia.com>
 <20220706062759.24946-9-nicolinc@nvidia.com>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220706062759.24946-9-nicolinc@nvidia.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?FW25mylLFsUnbbLT8GuwYAGaEQioW664t5vCnay2iSu3OQd+2u6/DkDH7qjI?=
 =?us-ascii?Q?Ek0cV7i3JV3XfPNAQiP0fJBSpBlDjcMfj3vjEw8J5EglI8S4rNWf3Q/6CcD0?=
 =?us-ascii?Q?PKphuhVwMhW/zIJ8P2fyM4mSXn2XhdP0gVGmlS6JiJ5JsnwatjmqQXzLqW6/?=
 =?us-ascii?Q?8oZZlNx0v1M9XcZUibQ0QGddVr+er4SdkukNda4sWU0Nsti0x+mCxm1SFLFa?=
 =?us-ascii?Q?zmPPMrul1K1850oHJ8W93Ka/loHPflZsVweFobJvR6Nb826D7qD9O2eF33wF?=
 =?us-ascii?Q?9WhAkDEymGOuIYTV7C+y52GdbHkQufFhhfSXp+zmNh2Iys7DHbPEcKl5IkRZ?=
 =?us-ascii?Q?jrMXPUDUjV2zPnIRRUqpn6Bgei2Hyr7bh6kv97rlOW7x9BTytq6T5gFIBpMn?=
 =?us-ascii?Q?O72FqHPxLPdxI9FN1T5RF6U8RILFYSa8YxA+LyVuphpf3oV6RosFpL+PxU26?=
 =?us-ascii?Q?zRzkRWMYkyNS+BIEcKCifVW5FzYaWDlyDtnL+AW2ULPNXS0+GL3zNS+hVqfA?=
 =?us-ascii?Q?5X6YZc0lWm4KkYNKJHlnYMdlOAhUeNWCQrZsjvI/SSd3m03MmS/zhAJrxLlg?=
 =?us-ascii?Q?9Kx4RV54uVqTCCGe0quqNkvENMv2Yg9fKI+DXWHOZOOC9MYiYbP0gVlzowxJ?=
 =?us-ascii?Q?J7qb2tfS5rJY86+i0rOd1QsmvMkyHh+GsxB382TB10kP8jf+3OA95njmd2ZY?=
 =?us-ascii?Q?QrY8DcKYGSpAnK4msb+4657yOkD6dWVArRy/uXEo/kgsG87u959niHCmwE+6?=
 =?us-ascii?Q?EoZ71IgHr8niNW3a07Wt7Hb+ciDBBxI6iy7NYiG25kZd6LXFDKv7qdHabrzJ?=
 =?us-ascii?Q?eBRbe3mczesu2zUY/76Ru701DXuipJsGCD4Wlo+nSN9fFy/Ssz8U/INbJeth?=
 =?us-ascii?Q?14vk3iAxp6Baq9u7hPYeQjKnUMuYof+Fg/nwyMDyOSTcavDMieO2gegvqC8k?=
 =?us-ascii?Q?ugJJJSTDhnyf1PrQKcbTTHhGOd5hV1l+BhrGwAiuEXldi9VTovGXi8BO86a2?=
 =?us-ascii?Q?J8V/APElEnYOVpD8G80jckvZFC58djyjJ5Gt1c9XL7vKOV/ef/vHXkkEMA6p?=
 =?us-ascii?Q?sdMgTlyrmYMUCitcmUVJScnqc4/IVXd5kBtFSvS8tE13cpgmPtDqbC9kBTkp?=
 =?us-ascii?Q?ylikwLBxW7QyngWXxjwnj5InqZeQPC99Gk0WBVwTtYkcr7Rea5jBi1U53gwP?=
 =?us-ascii?Q?ujCBJyZo0tACXECoFdKdhPR6RTafIkGRrpnyzCBLvnT7hdK1ZRESfaZmR95A?=
 =?us-ascii?Q?KQeHbq74sUkqs9yeCLmdgOEG3it+pYLB7iqJ8QTV/Lm51L4j210r0oNBQx3Z?=
 =?us-ascii?Q?XK0VsxaOSwGuAGr+Lh2Z+AR8eHK0n7e30iHOhI0VFBTVswsMJuRfHqGJpL+s?=
 =?us-ascii?Q?obc1VyF8phOecCuFcV4xMdbo202FhqdDgDO7vWRIottkcaLHcfOsEerXlwwq?=
 =?us-ascii?Q?k8K1OCvuEDvCmscIzpcGzO/JTV5kH1RJzHyU7IIZoHMTqboq4akWZOM25q9K?=
 =?us-ascii?Q?YYIPndM/Z+c0yigTr7ox8EYtwduj5Yazolf4jkt5Qu2IP39T+FbsI6KPNQsF?=
 =?us-ascii?Q?DJROoXT8hGBDA9SENdb66Bl7G0HQFRtP/QevXP+M?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: f95bc4ff-7b64-414a-86fc-08da5f7bbaf5
X-MS-Exchange-CrossTenant-AuthSource: MN2PR12MB4192.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Jul 2022 18:17:05.0646
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: O3a+ZyPY2LJd01cSjVrtFF5jWPWm/L5Fn056qIPPu+4tBX7vzDUfK4Mn7/tBjEKq
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR12MB4952
X-Spam-Status: No, score=-1.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,
        T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Jul 05, 2022 at 11:27:58PM -0700, Nicolin Chen wrote:
> A PFN is not secure enough to promise that the memory is not IO. And
> direct access via memcpy() that only handles CPU memory will crash on
> S390 if the PFN is an IO PFN, as we have to use the memcpy_to/fromio()
> that uses the special S390 IO access instructions. On the other hand,
> a "struct page *" is always a CPU coherent thing that fits memcpy().
> 
> Also, casting a PFN to "void *" for memcpy() is not a proper practice,
> kmap_local_page() is the correct API to call here, though S390 doesn't
> use highmem, which means kmap_local_page() is a NOP.
> 
> There's a following patch changing the vfio_pin_pages() API to return
> a list of "struct page *" instead of PFNs. It will block any IO memory
> from ever getting into this call path, for such a security purpose. In
> this patch, add kmap_local_page() to prepare for that.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason