diff options
Diffstat (limited to 'arch/arm64/kernel/fpsimd.c')
| -rw-r--r-- | arch/arm64/kernel/fpsimd.c | 187 |
1 files changed, 19 insertions, 168 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index ad8aebb1cdef..522df9c7f3a4 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -22,7 +22,6 @@ #include <linux/init.h> #include <linux/sched.h> #include <linux/signal.h> -#include <linux/hardirq.h> #include <asm/fpsimd.h> #include <asm/cputype.h> @@ -35,60 +34,6 @@ #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) @@ -126,137 +71,43 @@ void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs) 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)) + /* check if not kernel threads */ + if (current->mm) 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); - } + if (next->mm) + fpsimd_load_state(&next->thread.fpsimd_state); } 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(); - } + memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); + fpsimd_load_state(¤t->thread.fpsimd_state); 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) +void kernel_neon_begin(void) { - if (in_interrupt()) { - struct fpsimd_partial_state *s = this_cpu_ptr( - in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate); + /* Avoid using the NEON in interrupt context */ + BUG_ON(in_interrupt()); + preempt_disable(); - 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); - } + if (current->mm) + fpsimd_save_state(¤t->thread.fpsimd_state); } -EXPORT_SYMBOL(kernel_neon_begin_partial); +EXPORT_SYMBOL(kernel_neon_begin); 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(); - } + if (current->mm) + fpsimd_load_state(¤t->thread.fpsimd_state); + + preempt_enable(); } EXPORT_SYMBOL(kernel_neon_end); @@ -268,12 +119,12 @@ static int fpsimd_cpu_pm_notifier(struct notifier_block *self, { switch (cmd) { case CPU_PM_ENTER: - if (current->mm && !test_thread_flag(TIF_FOREIGN_FPSTATE)) + if (current->mm) fpsimd_save_state(¤t->thread.fpsimd_state); break; case CPU_PM_EXIT: if (current->mm) - set_thread_flag(TIF_FOREIGN_FPSTATE); + fpsimd_load_state(¤t->thread.fpsimd_state); break; case CPU_PM_ENTER_FAILED: default: |