4f27f6a04f
The aim is to take advantage of SSE instructions such as AES-NI in the kernel by lazily saving and restoring FPU state across system calls and pagefaults. (everything can can do I/O) This is accomplished by the functions fpusave() and fpurestore(). fpusave() remembers the current state and disables the FPU if it was active by setting the TS flag. In case the FPU gets used, the current state gets saved and a new PFPU.fpslot is allocated by mathemu(). fpurestore() restores the previous FPU state, reenabling the FPU if fpusave() disabled it. In the most common case, when userspace is not using the FPU, then fpusave()/fpurestore() just toggle the FPpush bit in up->fpstate. When the FPU was active, but we do not use the FPU, then nothing needs to be saved or restored. We just switched the TS flag on and off agaian. Note, this is done for the amd64 kernel only. |
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