diff options
| -rw-r--r-- | arch/x86/kernel/fpu/core.c | 25 |
1 files changed, 21 insertions, 4 deletions
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 90f624d68b26..779813126f49 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -284,10 +284,27 @@ int fpstate_alloc_init(struct task_struct *curr) EXPORT_SYMBOL_GPL(fpstate_alloc_init); /* - * The _current_ task is using the FPU for the first time - * so initialize it and set the mxcsr to its default - * value at reset if we support XMM instructions and then - * remember the current task has used the FPU. + * This function is called before we modify a stopped child's + * FPU state context. + * + * If the child has not used the FPU before then initialize its + * FPU context. + * + * If the child has used the FPU before then unlazy it. + * + * [ After this function call, after the context is modified and + * the child task is woken up, the child task will restore + * the modified FPU state from the modified context. If we + * didn't clear its lazy status here then the lazy in-registers + * state pending on its former CPU could be restored, losing + * the modifications. ] + * + * This function is also called before we read a stopped child's + * FPU state - to make sure it's modified. + * + * TODO: A future optimization would be to skip the unlazying in + * the read-only case, it's not strictly necessary for + * read-only access to the context. */ static int fpu__unlazy_stopped(struct task_struct *child) { |