svn commit: r338459 - head/sys/amd64/amd64

[Konstantin Belousov]

Author: kib
Date: Tue Sep  4 19:26:54 2018
New Revision: 338459
URL: https://svnweb.freebsd.org/changeset/base/338459

Log:
  amd64: For non-PTI mode, do not initialize PCPU kcr3 to KPML4phys.
  
  Non-PTI mode does not switch kcr3, which means that kcr3 is almost
  always stale.  This is important for the NMI handler, which reloads
  %cr3 with PCPU(kcr3) if the value is different from PMAP_NO_CR3.
  
  The end result is that curpmap in NMI handler does not match the page
  table loaded into hardware.  The manifestation was copyin(9) looping
  forever when a usermode access page fault cannot be resolved by
  vm_fault() updating a different page table.
  
  Reported by:	mmacy
  Reviewed by:	markj
  Sponsored by:	The FreeBSD Foundation
  MFC after:	3 days
  Approved by:	re (gjb)

Modified:
  head/sys/amd64/amd64/pmap.c

Modified: head/sys/amd64/amd64/pmap.c
==============================================================================
--- head/sys/amd64/amd64/pmap.c	Tue Sep  4 19:22:31 2018	(r338458)
+++ head/sys/amd64/amd64/pmap.c	Tue Sep  4 19:26:54 2018	(r338459)
@@ -7582,9 +7582,13 @@ pmap_activate_boot(pmap_t pmap)
 	CPU_SET(cpuid, &pmap->pm_active);
 #endif
 	PCPU_SET(curpmap, pmap);
-	kcr3 = pmap->pm_cr3;
-	if (pmap_pcid_enabled)
-		kcr3 |= pmap->pm_pcids[cpuid].pm_pcid | CR3_PCID_SAVE;
+	if (pti) {
+		kcr3 = pmap->pm_cr3;
+		if (pmap_pcid_enabled)
+			kcr3 |= pmap->pm_pcids[cpuid].pm_pcid | CR3_PCID_SAVE;
+	} else {
+		kcr3 = PMAP_NO_CR3;
+	}
 	PCPU_SET(kcr3, kcr3);
 	PCPU_SET(ucr3, PMAP_NO_CR3);
 }