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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: MdS81Emzv7M9jHcJoX2aO+ROOxgFDHfK8lQ2Ljn0hi+69BO+bTCEbcqGwZ7HvagxD5Wp2CU8M+d8H8ZEY+6aWi2w0CRg0GbxL09KsP1JDdXcbTM8w4HIfBoDbVNclzVSM0BXjRiHEeptpHcD/ew0JM5hYDWhevUwJOrCS74D7Aejygf7lgBv45TtvbwswDeELIe7/GCxrNU71Y3ycqbktVVceTO2GK+fQQGYK4qRagTdZ2cxzoNLg11XzSL0M/B+8rmZuDd7TirEFlA+qQxVmwzKE1RTpz0N6FGmkhFVsvKr5gd5yNeyk2mtbiuhLjElDjmdgAYkFYIVc+Nfrpk+CyrUetZRbTem0IgNIhA716oCtVASY5BiWptqs+XCNJliQsYJGxmfkv5XCMqyh5HeUhoSQFfqQBJ1CXivTYpJFhbqpcQH1WSADy4LLsB/iTGq X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Sep 2026 11:28:15.8882 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f0f98e52-f381-4b5d-b336-08df1253450a 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: AMS0EPF0000056B.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAXPR08MB6558 Reminder On 24/08/2026 5:04 pm, Muhammad Usama Anjum wrote: > With Hardware Tag-Based KASAN in asynchronous or asymmetric mode, kernel > nofault loops currently set and clear PSTATE.TCO around every access. > > Introduce bare nofault accessors, batching hooks, and an internal scope > guard. Convert maccess page-fault cleanup to scoped form. Skip > page-fault setup for zero-sized kernel nofault copies and zero-length > BPF string operations. Then use bare primitives in the maccess and BPF > loops. For non-empty operations, this reduces the code-derived dynamic > MSR TCO execution count from 2N to 2. Two-string BPF comparisons fall > from 4N to 2. > > The BPF changes and an earlier maccess implementation with explicit > cleanup were tested with QEMU arm64 using Hardware Tag-Based KASAN in > synchronous, asynchronous, and asymmetric modes. All nine arm64 MTE > kselftests passed in each mode, as did the 138 focused BPF string_kfuncs > and varlen subtests. The focused BPF tests also passed with the default > non-MTE arm64 CPU model. Both final maccess scoped-guard patches were > arm64 cross-built. Runtime tests have not been rerun after that > conversion. > > Muhammad Usama Anjum (7): > arm64: uaccess: Add batched kernel nofault accessors > uaccess: Add scope guard for bare kernel nofault regions > maccess: Skip setup for zero-sized kernel nofault copies > maccess: Use a scoped guard for page faults > maccess: Batch TCO handling in kernel nofault loops > bpf: Skip setup for zero-length string kfunc operations > bpf: Batch TCO handling in string kfuncs > > arch/arm64/include/asm/uaccess.h | 71 ++++++++++++++++++++++++-------- > include/linux/uaccess.h | 20 +++++++++ > kernel/bpf/helpers.c | 41 ++++++++++++------ > mm/maccess.c | 68 ++++++++++++++++-------------- > 4 files changed, 139 insertions(+), 61 deletions(-) > -- Thanks, Usama