diff options
Diffstat (limited to 'arch/arm64/kernel/fpsimd.c')
| -rw-r--r-- | arch/arm64/kernel/fpsimd.c | 172 |
1 files changed, 132 insertions, 40 deletions
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index c7b4995868e1..3a68cf38a6b3 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -17,16 +17,19 @@ * along with this program. If not, see <http://www.gnu.org/licenses/>. */ +#include <linux/bottom_half.h> #include <linux/cpu.h> #include <linux/cpu_pm.h> #include <linux/kernel.h> #include <linux/init.h> +#include <linux/percpu.h> +#include <linux/preempt.h> #include <linux/sched/signal.h> #include <linux/signal.h> -#include <linux/hardirq.h> #include <asm/fpsimd.h> #include <asm/cputype.h> +#include <asm/simd.h> #define FPEXC_IOF (1 << 0) #define FPEXC_DZF (1 << 1) @@ -62,6 +65,13 @@ * CPU currently contain the most recent userland FPSIMD state of the current * task. * + * In order to allow softirq handlers to use FPSIMD, kernel_neon_begin() may + * save the task's FPSIMD context back to task_struct from softirq context. + * To prevent this from racing with the manipulation of the task's FPSIMD state + * from task context and thereby corrupting the state, it is necessary to + * protect any manipulation of a task's fpsimd_state or TIF_FOREIGN_FPSTATE + * flag with local_bh_disable() unless softirqs are already masked. + * * 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 @@ -161,11 +171,14 @@ void fpsimd_flush_thread(void) { if (!system_supports_fpsimd()) return; - preempt_disable(); + + local_bh_disable(); + memset(¤t->thread.fpsimd_state, 0, sizeof(struct fpsimd_state)); fpsimd_flush_task_state(current); set_thread_flag(TIF_FOREIGN_FPSTATE); - preempt_enable(); + + local_bh_enable(); } /* @@ -176,10 +189,13 @@ void fpsimd_preserve_current_state(void) { if (!system_supports_fpsimd()) return; - preempt_disable(); + + local_bh_disable(); + if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) fpsimd_save_state(¤t->thread.fpsimd_state); - preempt_enable(); + + local_bh_enable(); } /* @@ -191,15 +207,18 @@ void fpsimd_restore_current_state(void) { if (!system_supports_fpsimd()) return; - preempt_disable(); + + local_bh_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); + __this_cpu_write(fpsimd_last_state, st); st->cpu = smp_processor_id(); } - preempt_enable(); + + local_bh_enable(); } /* @@ -211,15 +230,18 @@ void fpsimd_update_current_state(struct fpsimd_state *state) { if (!system_supports_fpsimd()) return; - preempt_disable(); + + local_bh_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); + __this_cpu_write(fpsimd_last_state, st); st->cpu = smp_processor_id(); } - preempt_enable(); + + local_bh_enable(); } /* @@ -232,52 +254,122 @@ void fpsimd_flush_task_state(struct task_struct *t) #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); +DEFINE_PER_CPU(bool, kernel_neon_busy); +EXPORT_PER_CPU_SYMBOL(kernel_neon_busy); /* * Kernel-side NEON support functions */ -void kernel_neon_begin_partial(u32 num_regs) + +/* + * kernel_neon_begin(): obtain the CPU FPSIMD registers for use by the calling + * context + * + * Must not be called unless may_use_simd() returns true. + * Task context in the FPSIMD registers is saved back to memory as necessary. + * + * A matching call to kernel_neon_end() must be made before returning from the + * calling context. + * + * The caller may freely use the FPSIMD registers until kernel_neon_end() is + * called. + */ +void kernel_neon_begin(void) { if (WARN_ON(!system_supports_fpsimd())) return; - 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); - } + BUG_ON(!may_use_simd()); + + local_bh_disable(); + + __this_cpu_write(kernel_neon_busy, true); + + /* Save unsaved task fpsimd state, if any: */ + if (current->mm && !test_and_set_thread_flag(TIF_FOREIGN_FPSTATE)) + fpsimd_save_state(¤t->thread.fpsimd_state); + + /* Invalidate any task state remaining in the fpsimd regs: */ + __this_cpu_write(fpsimd_last_state, NULL); + + preempt_disable(); + + local_bh_enable(); } -EXPORT_SYMBOL(kernel_neon_begin_partial); +EXPORT_SYMBOL(kernel_neon_begin); +/* + * kernel_neon_end(): give the CPU FPSIMD registers back to the current task + * + * Must be called from a context in which kernel_neon_begin() was previously + * called, with no call to kernel_neon_end() in the meantime. + * + * The caller must not use the FPSIMD registers after this function is called, + * unless kernel_neon_begin() is called again in the meantime. + */ void kernel_neon_end(void) { + bool busy; + if (!system_supports_fpsimd()) return; - 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(); - } + + busy = __this_cpu_xchg(kernel_neon_busy, false); + WARN_ON(!busy); /* No matching kernel_neon_begin()? */ + + preempt_enable(); } EXPORT_SYMBOL(kernel_neon_end); +static DEFINE_PER_CPU(struct fpsimd_state, efi_fpsimd_state); +static DEFINE_PER_CPU(bool, efi_fpsimd_state_used); + +/* + * EFI runtime services support functions + * + * The ABI for EFI runtime services allows EFI to use FPSIMD during the call. + * This means that for EFI (and only for EFI), we have to assume that FPSIMD + * is always used rather than being an optional accelerator. + * + * These functions provide the necessary support for ensuring FPSIMD + * save/restore in the contexts from which EFI is used. + * + * Do not use them for any other purpose -- if tempted to do so, you are + * either doing something wrong or you need to propose some refactoring. + */ + +/* + * __efi_fpsimd_begin(): prepare FPSIMD for making an EFI runtime services call + */ +void __efi_fpsimd_begin(void) +{ + if (!system_supports_fpsimd()) + return; + + WARN_ON(preemptible()); + + if (may_use_simd()) + kernel_neon_begin(); + else { + fpsimd_save_state(this_cpu_ptr(&efi_fpsimd_state)); + __this_cpu_write(efi_fpsimd_state_used, true); + } +} + +/* + * __efi_fpsimd_end(): clean up FPSIMD after an EFI runtime services call + */ +void __efi_fpsimd_end(void) +{ + if (!system_supports_fpsimd()) + return; + + if (__this_cpu_xchg(efi_fpsimd_state_used, false)) + fpsimd_load_state(this_cpu_ptr(&efi_fpsimd_state)); + else + kernel_neon_end(); +} + #endif /* CONFIG_KERNEL_MODE_NEON */ #ifdef CONFIG_CPU_PM |