/* * FP/SIMD context switching and fault handling * * Copyright (C) 2012 ARM Ltd. * Author: Catalin Marinas <catalin.marinas@arm.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ #include <linux/cpu_pm.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/sched.h> #include <linux/signal.h> #include <linux/hardirq.h> #include <asm/fpsimd.h> #include <asm/cputype.h> #define FPEXC_IOF (1 << 0) #define FPEXC_DZF (1 << 1) #define FPEXC_OFF (1 << 2) #define FPEXC_UFF (1 << 3) #define FPEXC_IXF (1 << 4) #define FPEXC_IDF (1 << 7) /* * In order to reduce the number of times the FPSIMD state is needlessly saved * and restored, we need to keep track of two things: * (a) for each task, we need to remember which CPU was the last one to have * the task's FPSIMD state loaded into its FPSIMD registers; * (b) for each CPU, we need to remember which task's userland FPSIMD state has * been loaded into its FPSIMD registers most recently, or whether it has * been used to perform kernel mode NEON in the meantime. * * For (a), we add a 'cpu' field to struct fpsimd_state, which gets updated to * the id of the current CPU everytime the state is loaded onto a CPU. For (b), * we add the per-cpu variable 'fpsimd_last_state' (below), which contains the * address of the userland FPSIMD state of the task that was loaded onto the CPU * the most recently, or NULL if kernel mode NEON has been performed after that. * * With this in place, we no longer have to restore the next FPSIMD state right * when switching between tasks. Instead, we can defer this check to userland * resume, at which time we verify whether the CPU's fpsimd_last_state and the * task's fpsimd_state.cpu are still mutually in sync. If this is the case, we * can omit the FPSIMD restore. * * As an optimization, we use the thread_info flag TIF_FOREIGN_FPSTATE to * indicate whether or not the userland FPSIMD state of the current task is * present in the registers. The flag is set unless the FPSIMD registers of this * CPU currently contain the most recent userland FPSIMD state of the current * task. * * For a certain task, the sequence may look something like this: * - the task gets scheduled in; if both the task's fpsimd_state.cpu field * contains the id of the current CPU, and the CPU's fpsimd_last_state per-cpu * variable points to the task's fpsimd_state, the TIF_FOREIGN_FPSTATE flag is * cleared, otherwise it is set; * * - the task returns to userland; if TIF_FOREIGN_FPSTATE is set, the task's * userland FPSIMD state is copied from memory to the registers, the task's * fpsimd_state.cpu field is set to the id of the current CPU, the current * CPU's fpsimd_last_state pointer is set to this task's fpsimd_state and the * TIF_FOREIGN_FPSTATE flag is cleared; * * - the task executes an ordinary syscall; upon return to userland, the * TIF_FOREIGN_FPSTATE flag will still be cleared, so no FPSIMD state is * restored; * * - the task executes a syscall which executes some NEON instructions; this is * preceded by a call to kernel_neon_begin(), which copies the task's FPSIMD * register contents to memory, clears the fpsimd_last_state per-cpu variable * and sets the TIF_FOREIGN_FPSTATE flag; * * - the task gets preempted after kernel_neon_end() is called; as we have not * returned from the 2nd syscall yet, TIF_FOREIGN_FPSTATE is still set so * whatever is in the FPSIMD registers is not saved to memory, but discarded. */ static DEFINE_PER_CPU(struct fpsimd_state *, fpsimd_last_state); /* * Trapped FP/ASIMD access. */ void do_fpsimd_acc(unsigned int esr, struct pt_regs *regs) { /* TODO: implement lazy context saving/restoring */ WARN_ON(1); } /* * Raise a SIGFPE for the current process. */ void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs) { siginfo_t info; unsigned int si_code = 0; if (esr & FPEXC_IOF) si_code = FPE_FLTINV; else if (esr & FPEXC_DZF) si_code = FPE_FLTDIV; else if (esr & FPEXC_OFF) si_code = FPE_FLTOVF; else if (esr & FPEXC_UFF) si_code = FPE_FLTUND; else if (esr & FPEXC_IXF) si_code = FPE_FLTRES; memset(&info, 0, sizeof(info)); info.si_signo = SIGFPE; info.si_code = si_code; info.si_addr = (void __user *)instruction_pointer(regs); send_sig_info(SIGFPE, &info, current); } void fpsimd_thread_switch(struct task_struct *next) { /* * Save the current FPSIMD state to memory, but only if whatever is in * the registers is in fact the most recent userland FPSIMD state of * 'current'. */ if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) fpsimd_save_state(¤t->thread.fpsimd_state); if (next->mm) { /* * If we are switching to a task whose most recent userland * FPSIMD state is already in the registers of *this* cpu, * we can skip loading the state from memory. Otherwise, set * the TIF_FOREIGN_FPSTATE flag so the state will be loaded * upon the next return to userland. */ struct fpsimd_state *st = &next->thread.fpsimd_state; if (__this_cpu_read(fpsimd_last_state) == st && st->cpu == smp_processor_id()) clear_ti_thread_flag(task_thread_info(next), TIF_FOREIGN_FPSTATE); else set_ti_thread_flag(task_thread_info(next), TIF_FOREIGN_FPSTATE); } } void fpsimd_flush_thread(void) { memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); set_thread_flag(TIF_FOREIGN_FPSTATE); } /* * Save the userland FPSIMD state of 'current' to memory, but only if the state * currently held in the registers does in fact belong to 'current' */ void fpsimd_preserve_current_state(void) { preempt_disable(); if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) fpsimd_save_state(¤t->thread.fpsimd_state); preempt_enable(); } /* * Load the userland FPSIMD state of 'current' from memory, but only if the * FPSIMD state already held in the registers is /not/ the most recent FPSIMD * state of 'current' */ void fpsimd_restore_current_state(void) { preempt_disable(); if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { struct fpsimd_state *st = ¤t->thread.fpsimd_state; fpsimd_load_state(st); this_cpu_write(fpsimd_last_state, st); st->cpu = smp_processor_id(); } preempt_enable(); } /* * Load an updated userland FPSIMD state for 'current' from memory and set the * flag that indicates that the FPSIMD register contents are the most recent * FPSIMD state of 'current' */ void fpsimd_update_current_state(struct fpsimd_state *state) { preempt_disable(); fpsimd_load_state(state); if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) { struct fpsimd_state *st = ¤t->thread.fpsimd_state; this_cpu_write(fpsimd_last_state, st); st->cpu = smp_processor_id(); } preempt_enable(); } /* * Invalidate live CPU copies of task t's FPSIMD state */ void fpsimd_flush_task_state(struct task_struct *t) { t->thread.fpsimd_state.cpu = NR_CPUS; } #ifdef CONFIG_KERNEL_MODE_NEON static DEFINE_PER_CPU(struct fpsimd_partial_state, hardirq_fpsimdstate); static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate); /* * Kernel-side NEON support functions */ void kernel_neon_begin_partial(u32 num_regs) { if (in_interrupt()) { struct fpsimd_partial_state *s = this_cpu_ptr( in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); BUG_ON(num_regs > 32); fpsimd_save_partial_state(s, roundup(num_regs, 2)); } else { /* * Save the userland FPSIMD state if we have one and if we * haven't done so already. Clear fpsimd_last_state to indicate * that there is no longer userland FPSIMD state in the * registers. */ preempt_disable(); if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE)) fpsimd_save_state(¤t->thread.fpsimd_state); this_cpu_write(fpsimd_last_state, NULL); } } EXPORT_SYMBOL(kernel_neon_begin_partial); void kernel_neon_end(void) { if (in_interrupt()) { struct fpsimd_partial_state *s = this_cpu_ptr( in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); fpsimd_load_partial_state(s); } else { preempt_enable(); } } EXPORT_SYMBOL(kernel_neon_end); #endif /* CONFIG_KERNEL_MODE_NEON */ #ifdef CONFIG_CPU_PM static int fpsimd_cpu_pm_notifier(struct notifier_block *self, unsigned long cmd, void *v) { switch (cmd) { case CPU_PM_ENTER: if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) fpsimd_save_state(¤t->thread.fpsimd_state); this_cpu_write(fpsimd_last_state, NULL); break; case CPU_PM_EXIT: if (current->mm) set_thread_flag(TIF_FOREIGN_FPSTATE); break; case CPU_PM_ENTER_FAILED: default: return NOTIFY_DONE; } return NOTIFY_OK; } static struct notifier_block fpsimd_cpu_pm_notifier_block = { .notifier_call = fpsimd_cpu_pm_notifier, }; static void fpsimd_pm_init(void) { cpu_pm_register_notifier(&fpsimd_cpu_pm_notifier_block); } #else static inline void fpsimd_pm_init(void) { } #endif /* CONFIG_CPU_PM */ /* * FP/SIMD support code initialisation. */ static int __init fpsimd_init(void) { u64 pfr = read_cpuid(ID_AA64PFR0_EL1); if (pfr & (0xf << 16)) { pr_notice("Floating-point is not implemented\n"); return 0; } elf_hwcap |= HWCAP_FP; if (pfr & (0xf << 20)) pr_notice("Advanced SIMD is not implemented\n"); else elf_hwcap |= HWCAP_ASIMD; fpsimd_pm_init(); return 0; } late_initcall(fpsimd_init);