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

- Fix typos.

- Move the compiler barrier comment to the top, because it's valid for the
  whole function, not just the legacy branch.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200818053130.GA3161093@gmail.com
Reviewed-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>

Author: ingomolnar

arch/x86/include/asm/sync_core.h

@@ -47,16 +47,19 @@ static inline void iret_to_self(void)
  *
  *  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();
@@ -67,10 +70,10 @@ static inline void sync_core(void)
 	 * For all other processors, there are quite a few ways to do this.
 	 * IRET-to-self is nice because it works on every CPU, at any CPL
 	 * (so it's compatible with paravirtualization), and it never exits
-	 * to a hypervisor. The only down sides are that it's a bit slow
+	 * 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,
@@ -81,9 +84,6 @@ static inline void sync_core(void)
 	 * 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();
 }