svn commit: r334003 - head/sys/amd64/amd64

[Konstantin Belousov]

Author: kib
Date: Mon May 21 21:05:55 2018
New Revision: 334003
URL: https://svnweb.freebsd.org/changeset/base/334003

Log:
  Preserve other bits in IA32_SPEC_CTL MSR when changing the IBRS and
  STIBP states.
  
  Tested by:	emaste (previous version)
  Sponsored by:	The FreeBSD Foundation
  MFC after:	3 days

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

Modified: head/sys/amd64/amd64/support.S
==============================================================================
--- head/sys/amd64/amd64/support.S	Mon May 21 21:04:31 2018	(r334002)
+++ head/sys/amd64/amd64/support.S	Mon May 21 21:05:55 2018	(r334003)
@@ -958,8 +958,9 @@ ENTRY(handle_ibrs_entry)
 	cmpb	$0,hw_ibrs_active(%rip)
 	je	1f
 	movl	$MSR_IA32_SPEC_CTRL,%ecx
-	movl	$(IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP),%eax
-	movl	$(IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP)>>32,%edx
+	rdmsr
+	orl	$(IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP),%eax
+	orl	$(IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP)>>32,%edx
 	wrmsr
 	movb	$1,PCPU(IBPB_SET)
 	testl	$CPUID_STDEXT_SMEP,cpu_stdext_feature(%rip)
@@ -972,8 +973,9 @@ ENTRY(handle_ibrs_exit)
 	cmpb	$0,PCPU(IBPB_SET)
 	je	1f
 	movl	$MSR_IA32_SPEC_CTRL,%ecx
-	xorl	%eax,%eax
-	xorl	%edx,%edx
+	rdmsr
+	andl	$~(IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP),%eax
+	andl	$~((IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP)>>32),%edx
 	wrmsr
 	movb	$0,PCPU(IBPB_SET)
 1:	ret
@@ -987,8 +989,9 @@ ENTRY(handle_ibrs_exit_rs)
 	pushq	%rdx
 	pushq	%rcx
 	movl	$MSR_IA32_SPEC_CTRL,%ecx
-	xorl	%eax,%eax
-	xorl	%edx,%edx
+	rdmsr
+	andl	$~(IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP),%eax
+	andl	$~((IA32_SPEC_CTRL_IBRS|IA32_SPEC_CTRL_STIBP)>>32),%edx
 	wrmsr
 	popq	%rcx
 	popq	%rdx