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Tue, 22 Jul 2025 01:40:05 +0000 Message-ID: Date: Mon, 21 Jul 2025 18:40:04 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/2] x86/fpu: Update the debug flow for x86_task_fpu() Content-Language: en-US To: Dave Hansen , Dave Hansen , CC: Borislav Petkov , "H . Peter Anvin" , "Thomas Gleixner" , Ingo Molnar , "Sean Christopherson" , Peter Zijlstra , Vignesh Balasubramanian , Rick Edgecombe , Oleg Nesterov , "Chang S . 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There are quite a few checks that special case PF_KTHREAD along with PF_USER_WORKER. For example, FPSTATE allocation and freeing as well as some context switch paths. Did I misinterpret something? I believe it originates here: https://lore.kernel.org/all/560c844c-f128-555b-40c6-31baff27537f@kernel.dk/ switch_fpu(): if (!test_tsk_thread_flag(old, TIF_NEED_FPU_LOAD) && cpu_feature_enabled(X86_FEATURE_FPU) && !(old->flags & (PF_KTHREAD | PF_USER_WORKER))) { struct fpu *old_fpu = x86_task_fpu(old); arch_release_task_struct(): if (fpu_state_size_dynamic() && !(tsk->flags & (PF_KTHREAD | PF_USER_WORKER))) fpstate_free(x86_task_fpu(tsk)); fpregs_restore_userregs(): if (WARN_ON_ONCE(current->flags & (PF_KTHREAD | PF_USER_WORKER))) return; kernel_fpu_begin_mask(): if (!(current->flags & (PF_KTHREAD | PF_USER_WORKER)) && !test_thread_flag(TIF_NEED_FPU_LOAD)) { set_thread_flag(TIF_NEED_FPU_LOAD); save_fpregs_to_fpstate(x86_task_fpu(current)); }