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Tue, 23 Mar 2021 11:07:25 +0000 From: Alistair Popple To: CC: David Hildenbrand , Miaohe Lin , , , , Subject: Re: [PATCH 3/5] mm/migrate.c: fix potential indeterminate pte entry in migrate_vma_insert_page() Date: Tue, 23 Mar 2021 22:07:23 +1100 Message-ID: <5999334.9xz1uWCbsP@nvdebian> In-Reply-To: <0bee2243-5771-4969-7b92-aaca67abc90c@redhat.com> References: <20210320093701.12829-1-linmiaohe@huawei.com> <20210320093701.12829-4-linmiaohe@huawei.com> <0bee2243-5771-4969-7b92-aaca67abc90c@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Originating-IP: [172.20.145.6] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 392122c8-7b54-49a3-fdfc-08d8edebd8d8 X-MS-TrafficTypeDiagnostic: BN8PR12MB3267: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:7691; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Mar 2021 11:07:28.3062 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 392122c8-7b54-49a3-fdfc-08d8edebd8d8 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT023.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR12MB3267 X-Stat-Signature: omhx1jg538ndckermz4fxbr8m1trtzqj X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: ABD6A4080F47 Received-SPF: none (nvidia.com>: No applicable sender policy available) receiver=imf17; identity=mailfrom; envelope-from=""; helo=NAM02-CY1-obe.outbound.protection.outlook.com; client-ip=40.107.76.53 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616497648-979831 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tuesday, 23 March 2021 9:26:43 PM AEDT David Hildenbrand wrote: > On 20.03.21 10:36, Miaohe Lin wrote: > > If the zone device page does not belong to un-addressable device memory, > > the variable entry will be uninitialized and lead to indeterminate pte > > entry ultimately. Fix this unexpectant case and warn about it. > > s/unexpectant/unexpected/ > > > > > Fixes: df6ad69838fc ("mm/device-public-memory: device memory cache coherent with CPU") > > Signed-off-by: Miaohe Lin > > --- > > mm/migrate.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/mm/migrate.c b/mm/migrate.c > > index 20a3bf75270a..271081b014cb 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -2972,6 +2972,13 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate, > > > > swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE); > > entry = swp_entry_to_pte(swp_entry); > > + } else { > > + /* > > + * For now we only support migrating to un-addressable > > + * device memory. > > + */ > > + WARN_ON(1); > > + goto abort; > > Fix it by crashing the kernel with panic_on_warn? :) > > If this case can actual happen, than no WARN_ON() - rather a > pr_warn_once(). If this case cannot happen, why do we even care (it's > not a fix then)? There is also already a check for this case in migrate_vma_pages(). The problem is it happens after the call to migrate_vma_insert_page(). I wonder if instead it would be better just to move the existing check to before that call?