x86/cpu: Fix typos and improve the comments in sync_core()

 *

 *  b) Text was modified on a different CPU, may subsequently be

 *     executed on this CPU, and you want to make sure the new version

 *     gets executed.  This generally means you're calling this in a IPI.

 *     gets executed.  This generally means you're calling this in an IPI.

 *

 * If you're calling this for a different reason, you're probably doing

 * it wrong.

 *

 * Like all of Linux's memory ordering operations, this is a

 * compiler barrier as well.

 */

static inline void sync_core(void)

{

	/*

	 * The SERIALIZE instruction is the most straightforward way to

	 * do this but it not universally available.

	 * do this, but it is not universally available.

	 */

	if (static_cpu_has(X86_FEATURE_SERIALIZE)) {

		serialize();

	 * (so it's compatible with paravirtualization), and it never exits

	 * to a hypervisor.  The only downsides are that it's a bit slow

	 * (it seems to be a bit more than 2x slower than the fastest

	 * options) and that it unmasks NMIs.  The "push %cs" is needed

	 * because, in paravirtual environments, __KERNEL_CS may not be a

	 * options) and that it unmasks NMIs.  The "push %cs" is needed,

	 * because in paravirtual environments __KERNEL_CS may not be a

	 * valid CS value when we do IRET directly.

	 *

	 * In case NMI unmasking or performance ever becomes a problem,

	 * CPUID is the conventional way, but it's nasty: it doesn't

	 * exist on some 486-like CPUs, and it usually exits to a

	 * hypervisor.

	 *

	 * Like all of Linux's memory ordering operations, this is a

	 * compiler barrier as well.

	 */

	iret_to_self();

}