Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: [PATCH 6/6] xen/x86: restrict PV Dom0 identity mapping
From:   Jan Beulich <jbeulich@suse.com>
To:     Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
References: <022b1a5e-4121-6bae-f07c-4ad5eac12481@suse.com>
Message-ID: <038b8c02-3621-d66a-63ae-982ccf67ae88@suse.com>
Date:   Thu, 30 Sep 2021 14:37:19 +0200
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.14.0
In-Reply-To: <022b1a5e-4121-6bae-f07c-4ad5eac12481@suse.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?M2p2R1N1S3czTkRsYXdxQ2MwZjdXdlAzVlYrVkRFWmNXVzhveTlQWlo4cWpE?=
 =?utf-8?B?dE1tNmNZUEcrU244WGl0c2Q5eWhhMXQ2WHQ5ck9qVDlEb1VCZnNaS0RCT0Vt?=
 =?utf-8?B?K2dXWWtLMm1DYWF4cjd4NDA1MEEvWXlnaU9jY0NkME9iTzFVbk01c2o0b2lW?=
 =?utf-8?B?MlJrK3R5d2Z0Y0kvTW1yck1PWHhEM3lIeUVmdVFscjZnZXFPMHJUcVFDV3kw?=
 =?utf-8?B?cjM4K0V5dEQrajhZT2dWMzhPdWNUWVZsUU9OSTlQTzNNL2tENlhMcld3NWRF?=
 =?utf-8?B?VWRaVCtKdnBrdmo3NkE3SWRQeUhURy9tV0YwcjlLYmdxZkVGTm9hTGdCdkFn?=
 =?utf-8?B?WUwwQmFpZDE3RUlDck8rdW53QWRERzJuRm51YVI3QTk0WlNGTWZWMFE3VXJY?=
 =?utf-8?B?aWRTdnBwWE9oZFhvLy9aMitGRUxUZENJcVhSRnhscC9pZUM5aVRZdlRyaWZU?=
 =?utf-8?B?cnYyUFVCS2NIcmxnNm05L2diNUVhaTN4NnFUeng4OWlpSGpjem9hcjI0MXhL?=
 =?utf-8?B?ZHp3MWRMQXc2QmhwK21XUVBHTHAxS2dwZ2Znc1pEbWY5eHdkYm9icmJFa09I?=
 =?utf-8?B?aU01ZGF0Qm13K3VsQnJYUHlQRSt5bENUeDRHcGFyNDg3WEZvd0M2V05oTk1W?=
 =?utf-8?B?STd3T1c1ZkcvSjdrSmJxRjFkNVBqZm5vdjVvWTFWRlRpNXpaakJ4NnlJTFdJ?=
 =?utf-8?B?dTlsMjV1N1JTQ01NWllUZW0wbUJZZ3NucnBzYno4a2dpT2JneVRFTURaQnZm?=
 =?utf-8?B?Ym9pbXdwUURvL0VvcEkxNEVIRHJDQWRIbmIzbXZseDNIZURDZ1FtaTNDUUh6?=
 =?utf-8?B?RjlGUGJKK1RYLzZGN29TYSs2eUg3dHhYNkJwR2pPeTZjRDhNM0Jsc2FFUTVt?=
 =?utf-8?B?Um9kRUxGU0E5c0QrRDBadis0VkVoa1Vqc3VzK0plMFE1R2UzNGJxZlZWZjd6?=
 =?utf-8?B?UWVrTVY1SS9nQmtTYkF6N1hFUW5iSVIxK0xxWWZwYmMrbnlxNlZ6c3g4ajNm?=
 =?utf-8?B?dzJsWGlYemxKWVhTRjhnVWhqVEJ2M3B2QmJoR0toNXZxNy9mdUNZZlhmRzlG?=
 =?utf-8?B?cjB1NTFEaklGcU1rTWQrc3dod2pEanpybWVhTzI3WEZEY1phQU9vbW9vT3dL?=
 =?utf-8?B?UGhCSFNIWU1JcDRPbnhmV05OYkNRRFRjY1R1Z2xRVHFSdHBCNXM3RWRWV3pk?=
 =?utf-8?B?UXYwL2prWnJ2R2VxZ055bXp5cGxzZVlKaFFrZTZWUXpEeCsrbUxtN3NRNVN3?=
 =?utf-8?B?d1ZMbEk1NTIzL2ZFalJ4Tm5vVmZBV1RPWUlOQWR6NXlkNFg5OGFIN1FsVlE5?=
 =?utf-8?B?WklRckQvRVV4aEJXUUdjQjJhSDJlc00xVmpvUW9Ba2pwSS95dzVtL3JlNm82?=
 =?utf-8?B?S3NNL0kwVDA5azBYOXNZdlVld1RuY0dnN2I2ZDkvYmRUY01FWVN3OExYUHAr?=
 =?utf-8?B?TkJpbk1XdXZEZVVheXh6UW45VFdqQUJQT0VjczYyNlVsTmlCVmozd21FMzJB?=
 =?utf-8?B?cmtkYzBrRCttcXlOK0h4eEo0aFIzZldyajA0UWN1WkxiRXBiMkgwZXdHWG9G?=
 =?utf-8?B?RkpnZWh2QXhTdHJPRnlJbEhkM1o4ZnJKczVMYmNwd1Vldk5GYWJ3TExIZ2xh?=
 =?utf-8?B?SUx1aC94eXIvTGNlWEhlNERJeEpyYVRuN3c0eWtweU5XYjI5TW5ZL0pzemY4?=
 =?utf-8?B?WFBEYXlEZFVqRmFHclJQRndWNzBpUEU0NFM4bEpRM0xaVWVCQ3ZzMGgySXgx?=
 =?utf-8?Q?93ZKV8oWsM+vckc/XhkCzli11oCJHU6m/B8ieBu?=
X-OriginatorOrg: suse.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 2cfb7984-2657-4317-0ae4-08d9840f0c60
X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB5600.eurprd04.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Sep 2021 12:37:21.8021
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: N+68ucEy+pC2zMfLvWa3YBirMpv4MDFLr5fQVKEKl3arg/Yr/kg/vljVeeZ6LHuxaQ1Uv2OjsEoU6X25wHf1UQ==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR04MB5600
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

When moving away RAM pages, there having been a mapping of those is not
a proper indication that instead MMIO should be mapped there. At the
point in time this effectively covers the low megabyte only. Mapping of
that is, however, the job of init_mem_mapping(). Comparing the two one
can also spot that we've been wrongly (or at least inconsistently) using
PAGE_KERNEL_IO here.

Simply zap any such mappings instead.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -425,13 +425,13 @@ static unsigned long __init xen_set_iden
 	}
 
 	/*
-	 * If the PFNs are currently mapped, the VA mapping also needs
-	 * to be updated to be 1:1.
+	 * If the PFNs are currently mapped, their VA mappings need to be
+	 * zapped.
 	 */
 	for (pfn = start_pfn; pfn <= max_pfn_mapped && pfn < end_pfn; pfn++)
 		(void)HYPERVISOR_update_va_mapping(
 			(unsigned long)__va(pfn << PAGE_SHIFT),
-			mfn_pte(pfn, PAGE_KERNEL_IO), 0);
+			native_make_pte(0), 0);
 
 	return remap_pfn;
 }