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Wed, 25 Jun 2025 16:06:29 -0700 Date: Wed, 25 Jun 2025 16:06:27 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "corbet@lwn.net" , "will@kernel.org" , "bagasdotme@gmail.com" , "robin.murphy@arm.com" , "joro@8bytes.org" , "thierry.reding@gmail.com" , "vdumpa@nvidia.com" , "jonathanh@nvidia.com" , "shuah@kernel.org" , "jsnitsel@redhat.com" , "nathan@kernel.org" , "peterz@infradead.org" , "Liu, Yi L" , "mshavit@google.com" , "praan@google.com" , "zhangzekun11@huawei.com" , "iommu@lists.linux.dev" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-tegra@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "patches@lists.linux.dev" , "mochs@nvidia.com" , "alok.a.tiwari@oracle.com" , "vasant.hegde@amd.com" , "dwmw2@infradead.org" , "baolu.lu@linux.intel.com" Subject: Re: [PATCH v6 10/25] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC ioctl Message-ID: References: <7dfb002613f224f57a069d27e7bf2b306b0a5ba0.1749884998.git.nicolinc@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Jun 2025 23:06:49.3675 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: cb8a59f8-8666-4583-07f8-08ddb43cf73e X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN1PEPF0000468C.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA5PPF9BB0D8619 On Wed, Jun 25, 2025 at 03:45:08AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Saturday, June 14, 2025 3:15 PM > > + > > + offset = > > + cmd->nesting_parent_iova - PAGE_ALIGN(cmd- > > >nesting_parent_iova); > > + max_npages = DIV_ROUND_UP(offset + cmd->length, PAGE_SIZE); > > + > > + /* > > + * FIXME allocation may fail when sizeof(*pages) * max_npages is > > + * larger than PAGE_SIZE. This might need a new API returning a > > + * bio_vec or something more efficient. > > + */ > > + pages = kcalloc(max_npages, sizeof(*pages), GFP_KERNEL); > > + if (!pages) > > + return ERR_PTR(-ENOMEM); > > + > > any allocation may fail... can you elaborate more here? How does > PAGE_SIZE become a boundary? Memory fragmentation can be the reason. It's easy to get one page but not for contiguous pages. Jason suggested to use kvcalloc, so I am adding this: @@ -249,11 +249,10 @@ iommufd_hw_queue_alloc_phys(struct iommu_hw_queue_alloc *cmd, max_npages = DIV_ROUND_UP(offset + cmd->length, PAGE_SIZE); /* - * FIXME allocation may fail when sizeof(*pages) * max_npages is - * larger than PAGE_SIZE. This might need a new API returning a - * bio_vec or something more efficient. + * Use kvcalloc() to avoid memory fragmentation for a large page array. + * Set __GFP_NOWARN to avoid syzkaller blowups */ - pages = kcalloc(max_npages, sizeof(*pages), GFP_KERNEL); + pages = kvcalloc(max_npages, sizeof(*pages), GFP_KERNEL | __GFP_NOWARN); if (!pages) return ERR_PTR(-ENOMEM); Thanks Nicolin