Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 pti updates from Ingo Molnar:
 "The main changes:

   - Make the IBPB barrier more strict and add STIBP support (Jiri
     Kosina)

   - Micro-optimize and clean up the entry code (Andy Lutomirski)

   - ... plus misc other fixes"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation: Propagate information about RSB filling mitigation to sysfs
  x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation
  x86/speculation: Apply IBPB more strictly to avoid cross-process data leak
  x86/speculation: Add RETPOLINE_AMD support to the inline asm CALL_NOSPEC variant
  x86/CPU: Fix unused variable warning when !CONFIG_IA32_EMULATION
  x86/pti/64: Remove the SYSCALL64 entry trampoline
  x86/entry/64: Use the TSS sp2 slot for SYSCALL/SYSRET scratch space
  x86/entry/64: Document idtentry

arch/x86/include/asm/processor.h

@@ -316,7 +316,13 @@ struct x86_hw_tss {
 	 */
 	u64			sp1;
 
+	/*
+	 * Since Linux does not use ring 2, the 'sp2' slot is unused by
+	 * hardware.  entry_SYSCALL_64 uses it as scratch space to stash
+	 * the user RSP value.
+	 */
 	u64			sp2;
+
 	u64			reserved2;
 	u64			ist[7];
 	u32			reserved3;