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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Jul 2025 08:35:04.0777 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f1d4496f-4250-4fba-6e98-08ddc8faa7f7 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: DU6PEPF0000B61D.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR08MB6347 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250722_013511_658941_50093792 X-CRM114-Status: GOOD ( 25.22 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Mark, > > Current futex atomic operations are implemented with ll/sc instructions and > > clearing PSTATE.PAN. > > > > Since Armv9.6, FEAT_LSUI supplies not only load/store instructions but > > also atomic operation for user memory access in kernel it doesn't need > > to clear PSTATE.PAN bit anymore. > > > > With theses instructions some of futex atomic operations don't need to > > be implmented with ldxr/stlxr pair instead can be implmented with > > one atomic operation supplied by FEAT_LSUI. > > > > However, some of futex atomic operations still need to use ll/sc way > > via ldtxr/stltxr supplied by FEAT_LSUI since there is no correspondant > > atomic instruction or doesn't support word size operation > > (i.e) eor, cas{mb}t But It's good to work without clearing PSTATE.PAN bit. > > That's unfortunate; have we fed back to Arm's architecture folks that we > care about those cases? I haven’t done so yet. If you don’t mind, could you let me know the appropriate person to give the feedback to? > > > Signed-off-by: Yeoreum Yun > > --- > > arch/arm64/include/asm/futex_lsui.h | 132 ++++++++++++++++++++++++++++ > > 1 file changed, 132 insertions(+) > > create mode 100644 arch/arm64/include/asm/futex_lsui.h > > This logic is introduced unused, and TBH I don't think this needs to be > in a separate header. > > I reckon it's be better to keep all of this in and rework > the series to: > > (1) Factor out the existing LL/SC logic into separate LL/SC helpers in > , with an __llsc_ prefix, called by the existing > functions. > > (2) Add the new __lsui_ futex operations to , along with > code to select between the __llsc_ and __lsui_ versions. > > We split the regular atomics different becuase there are *many* generic > atomic operations, but I don't think it's worthwhile to split the futex > logic over several headers. > > Maybe it's worth having , but for now I reckon it's best to > also fold that into , and we can split it out later if we > need it for something else. Thanks for your suggestion. I’ll rework it while keeping this implementation. Thanks! -- Sincerely, Yeoreum Yun