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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Jul 2025 04:24:39.7631 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 39a7838f-6be2-42d0-f9a4-08ddcb332c00 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS0EPF000001A3.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB10453 X-Stat-Signature: n3z3zt6eutkmkho68u5k8o3iay6a63jw X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: EF61FC0002 X-Rspam-User: X-HE-Tag: 1753417485-168940 X-HE-Meta: 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 gUIKc9Ha 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 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: List-Subscribe: List-Unsubscribe: On 24/07/25 5:28 pm, Catalin Marinas wrote: > On Thu, Jul 24, 2025 at 04:10:18PM +0530, Dev Jain wrote: >> On 24/07/25 1:49 pm, Catalin Marinas wrote: >>> On Thu, Jul 03, 2025 at 08:44:41PM +0530, Dev Jain wrote: >>>> arm64 currently changes permissions on vmalloc objects locklessly, via >>>> apply_to_page_range, whose limitation is to deny changing permissions for >>>> block mappings. Therefore, we move away to use the generic pagewalk API, >>>> thus paving the path for enabling huge mappings by default on kernel space >>>> mappings, thus leading to more efficient TLB usage. However, the API >>>> currently enforces the init_mm.mmap_lock to be held. To avoid the >>>> unnecessary bottleneck of the mmap_lock for our usecase, this patch >>>> extends this generic API to be used locklessly, so as to retain the >>>> existing behaviour for changing permissions. >>> Is it really a significant bottleneck if we take the lock? I suspect if >>> we want to make this generic and allow splitting, we'll need a lock >>> anyway (though maybe for shorter intervals if we only split the edges). >> The splitting primitive may or may not require a lock, Ryan and Yang had >> some discussion on the linear map block mapping thread. I am assuming >> that since we didn't need a lock in the past, there is no need to take it now, >> since we are only changing the pagetable walk API being used. > I vaguely remember Ryan's and Yang's discussion. I'd have to revisit it. > In the past we were not replacing block/table entries since there was no > page table splitting. If we are to add some splitting, even at the > edges, what would prevent some other caller of this API overlapping and > attempting to do the same split? It's not just vmalloc ranges but the > linear map as well that's touched by __change_memory_common(). Sorry I wasn't clear enough, what I meant to say was that the locking will be the concernment of the splitting primitive - once that is done, update_range_prot() does not need to take the lock. >