svn commit: r345225 - head/sys/amd64/amd64

[Konstantin Belousov]

Author: kib
Date: Sat Mar 16 11:12:02 2019
New Revision: 345225
URL: https://svnweb.freebsd.org/changeset/base/345225

Log:
  amd64: rewrite cpu_switch.S fragment to reload tss.rsp0 on context switch.
  
  New code avoids jumps.
  
  Reviewed by:	markj
  Tested by:	pho
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week
  Differential revision:	https://reviews.freebsd.org/D19514

Modified:
  head/sys/amd64/amd64/cpu_switch.S

Modified: head/sys/amd64/amd64/cpu_switch.S
==============================================================================
--- head/sys/amd64/amd64/cpu_switch.S	Sat Mar 16 10:51:11 2019	(r345224)
+++ head/sys/amd64/amd64/cpu_switch.S	Sat Mar 16 11:12:02 2019	(r345225)
@@ -209,14 +209,11 @@ do_kthread:
 done_tss:
 	movq	%r8,PCPU(RSP0)
 	movq	%r8,PCPU(CURPCB)
-	/* Update the TSS_RSP0 pointer for the next interrupt */
-	cmpq	$~0,PCPU(UCR3)
-	je	1f
 	movq	PCPU(PTI_RSP0),%rax
+	cmpq	$~0,PCPU(UCR3)
+	cmove	%r8,%rax
 	movq	%rax,TSS_RSP0(%rdx)
-	jmp	2f
-1:	movq	%r8,TSS_RSP0(%rdx)
-2:	movq	%r12,PCPU(CURTHREAD)		/* into next thread */
+	movq	%r12,PCPU(CURTHREAD)		/* into next thread */
 
 	/* Test if debug registers should be restored. */
 	testl	$PCB_DBREGS,PCB_FLAGS(%r8)