diff options
| -rw-r--r-- | arch/x86/include/asm/fpu/api.h | 17 | ||||
| -rw-r--r-- | arch/x86/kernel/fpu/core.c | 17 |
2 files changed, 20 insertions, 14 deletions
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index f86ad3335529..f42de5f05e7e 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -16,10 +16,9 @@ /* * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It - * disables preemption so be careful if you intend to use it for long periods - * of time. - * If you intend to use the FPU in irq/softirq you need to check first with - * irq_fpu_usable() if it is possible. + * disables preemption and softirq processing, so be careful if you intend to + * use it for long periods of time. Kernel-mode FPU cannot be used in all + * contexts -- see irq_fpu_usable() for details. */ /* Kernel FPU states to initialize in kernel_fpu_begin_mask() */ @@ -50,10 +49,10 @@ static inline void kernel_fpu_begin(void) } /* - * Use fpregs_lock() while editing CPU's FPU registers or fpu->fpstate. - * A context switch will (and softirq might) save CPU's FPU registers to - * fpu->fpstate.regs and set TIF_NEED_FPU_LOAD leaving CPU's FPU registers in - * a random state. + * Use fpregs_lock() while editing CPU's FPU registers or fpu->fpstate, or while + * using the FPU in kernel mode. A context switch will (and softirq might) save + * CPU's FPU registers to fpu->fpstate.regs and set TIF_NEED_FPU_LOAD leaving + * CPU's FPU registers in a random state. * * local_bh_disable() protects against both preemption and soft interrupts * on !RT kernels. @@ -63,8 +62,6 @@ static inline void kernel_fpu_begin(void) * preemptible. Disabling preemption is the right choice here as bottom * half processing is always in thread context on RT kernels so it * implicitly prevents bottom half processing as well. - * - * Disabling preemption also serializes against kernel_fpu_begin(). */ static inline void fpregs_lock(void) { diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 36df548acc40..422c98ca6eb8 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -60,9 +60,16 @@ bool irq_fpu_usable(void) if (WARN_ON_ONCE(in_nmi())) return false; - /* In kernel FPU usage already active? */ - if (this_cpu_read(in_kernel_fpu)) + /* + * In kernel FPU usage already active? This detects any explicitly + * nested usage in task or softirq context, which is unsupported. It + * also detects attempted usage in a hardirq that has interrupted a + * kernel-mode FPU section. + */ + if (this_cpu_read(in_kernel_fpu)) { + WARN_ON_FPU(!in_hardirq()); return false; + } /* * When not in NMI or hard interrupt context, FPU can be used in: @@ -420,7 +427,8 @@ EXPORT_SYMBOL_GPL(fpu_copy_uabi_to_guest_fpstate); void kernel_fpu_begin_mask(unsigned int kfpu_mask) { - preempt_disable(); + if (!irqs_disabled()) + fpregs_lock(); WARN_ON_FPU(!irq_fpu_usable()); WARN_ON_FPU(this_cpu_read(in_kernel_fpu)); @@ -448,7 +456,8 @@ void kernel_fpu_end(void) WARN_ON_FPU(!this_cpu_read(in_kernel_fpu)); this_cpu_write(in_kernel_fpu, false); - preempt_enable(); + if (!irqs_disabled()) + fpregs_unlock(); } EXPORT_SYMBOL_GPL(kernel_fpu_end); |