--- zzzz-none-000/linux-3.10.107/arch/arm64/kernel/fpsimd.c 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/arch/arm64/kernel/fpsimd.c 2021-02-04 17:41:59.000000000 +0000 @@ -17,10 +17,13 @@ * along with this program. If not, see . */ +#include +#include #include #include #include #include +#include #include #include @@ -33,6 +36,60 @@ #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) @@ -70,38 +127,220 @@ void fpsimd_thread_switch(struct task_struct *next) { - /* check if not kernel threads */ - if (current->mm) + /* + * 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) - fpsimd_load_state(&next->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) { - preempt_disable(); memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); - fpsimd_load_state(¤t->thread.fpsimd_state); + fpsimd_flush_task_state(current); + 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 */ + +#ifdef CONFIG_HOTPLUG_CPU +static int fpsimd_cpu_hotplug_notifier(struct notifier_block *nfb, + unsigned long action, + void *hcpu) +{ + unsigned int cpu = (long)hcpu; + + switch (action) { + case CPU_DEAD: + case CPU_DEAD_FROZEN: + per_cpu(fpsimd_last_state, cpu) = NULL; + break; + } + return NOTIFY_OK; +} + +static struct notifier_block fpsimd_cpu_hotplug_notifier_block = { + .notifier_call = fpsimd_cpu_hotplug_notifier, +}; + +static inline void fpsimd_hotplug_init(void) +{ + register_cpu_notifier(&fpsimd_cpu_hotplug_notifier_block); +} + +#else +static inline void fpsimd_hotplug_init(void) { } +#endif + +/* * FP/SIMD support code initialisation. */ static int __init fpsimd_init(void) { - u64 pfr = read_cpuid(ID_AA64PFR0_EL1); - - if (pfr & (0xf << 16)) { + if (elf_hwcap & HWCAP_FP) { + fpsimd_pm_init(); + fpsimd_hotplug_init(); + } else { pr_notice("Floating-point is not implemented\n"); - return 0; } - elf_hwcap |= HWCAP_FP; - if (pfr & (0xf << 20)) + if (!(elf_hwcap & HWCAP_ASIMD)) pr_notice("Advanced SIMD is not implemented\n"); - else - elf_hwcap |= HWCAP_ASIMD; return 0; }