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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Sep 2025 12:58:10.7574 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a6de652d-0818-4e50-97b7-08ddf5e9db1a 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: DB1PEPF000509F7.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PR3PR08MB5708 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250917_055823_990525_A8C61EB2 X-CRM114-Status: GOOD ( 14.10 ) 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, > +LSUI_FUTEX_ATOMIC_OP(add, ldtadd, al) > +LSUI_FUTEX_ATOMIC_OP(or, ldtset, al) > +LSUI_FUTEX_ATOMIC_OP(andnot, ldtclr, al) > +LSUI_FUTEX_ATOMIC_OP(set, swpt, al) > + > +static __always_inline int > +__lsui_cmpxchg64(u64 __user *uaddr, u64 *oldval, u64 newval) > +{ > + int ret = 0; > + > + asm volatile("// __lsui_cmpxchg64\n" > + __LSUI_PREAMBLE > +"1: casalt %x2, %x3, %1\n" > +"2:\n" > + _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w0) > + : "+r" (ret), "+Q" (*uaddr), "+r" (*oldval) > + : "r" (newval) > + : "memory"); > + > + return ret; > +} > + > +static __always_inline int > +__lsui_cmpxchg32(u32 __user *uaddr, u32 oldval, u32 newval, u32 *oval) > +{ > + u64 __user *uaddr_al; > + u64 oval64, nval64, tmp; > + static const u64 hi_mask = IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? > + GENMASK_U64(63, 32): GENMASK_U64(31, 0); > + static const u8 hi_shift = IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? 32 : 0; > + static const u8 lo_shift = IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? 0 : 32; > + > + uaddr_al = (u64 __user *) PTR_ALIGN_DOWN(uaddr, sizeof(u64)); > + if (get_user(oval64, uaddr_al)) > + return -EFAULT; > + > + if ((u32 __user *)uaddr_al != uaddr) { > + nval64 = ((oval64 & ~hi_mask) | ((u64)newval << hi_shift)); > + oval64 = ((oval64 & ~hi_mask) | ((u64)oldval << hi_shift)); > + } else { > + nval64 = ((oval64 & hi_mask) | ((u64)newval << lo_shift)); > + oval64 = ((oval64 & hi_mask) | ((u64)oldval << lo_shift)); > + } > + > + tmp = oval64; > + > + if (__lsui_cmpxchg64(uaddr_al, &oval64, nval64)) > + return -EFAULT; > + > + if (tmp != oval64) > + return -EAGAIN; > + > + *oval = oldval; > + > + return 0; > +} > + While I see the code I couldn't erase some suspicion because of below questions...: 1. Suppose there is structure: struct s_test { u32 futex; u32 others; }; Before CPU0 executing casalt futex, CPU1 executes the store32_rel() on others. Then, Can CPU0 can observe the CPU1's store32_rel() since casalt operates with &futex, but CPU1 operates with &others. CPU0 CPU1 ... store32_rel(&s_test->others); /// can this see CPU1's modification? casalt(..., ..., &s_test->futex); 2. Suppose there is structure: struct s_test { u32 others; u32 futex; }; Then, can below "ldtr" be reordered after casalt? ldtr(&s_test->futex); ... casalt(..., ..., &s_test->others); I think the both cases can break the memory consistency unintensionaly in the view of user... Well, the dmb ish; could be solved the above problem before casalt, However, It seems it's much better to return former ll/sc method...? Thanks! -- Sincerely, Yeoreum Yun