svn commit: r349442 - head/sys/arm64/arm64

[Alan Cox]

Author: alc
Date: Wed Jun 26 21:43:41 2019
New Revision: 349442
URL: https://svnweb.freebsd.org/changeset/base/349442

Log:
  Revert one of the changes from r349323.  Specifically, undo the change
  that replaced a pmap_invalidate_page() with a dsb(ishst) in
  pmap_enter_quick_locked().  Even though this change is in principle
  correct, I am seeing occasional, spurious bus errors that are only
  reproducible without this pmap_invalidate_page().  (None of adding an
  isb, "upgrading" the dsb to wait on loads as well as stores, or
  disabling superpage mappings eliminates the bus errors.)  Add an XXX
  comment explaining why the pmap_invalidate_page() is being performed.
  
  Discussed with:	     andrew, markj

Modified:
  head/sys/arm64/arm64/pmap.c

Modified: head/sys/arm64/arm64/pmap.c
==============================================================================
--- head/sys/arm64/arm64/pmap.c	Wed Jun 26 21:19:43 2019	(r349441)
+++ head/sys/arm64/arm64/pmap.c	Wed Jun 26 21:43:41 2019	(r349442)
@@ -3758,7 +3758,15 @@ pmap_enter_quick_locked(pmap_t pmap, vm_offset_t va, v
 		cpu_icache_sync_range(PHYS_TO_DMAP(pa), PAGE_SIZE);
 
 	pmap_load_store(l3, l3_val);
-	dsb(ishst);
+
+	/*
+	 * XXX In principle, because this L3 entry was invalid, we should not
+	 * need to perform a TLB invalidation here.  However, in practice,
+	 * when simply performing a "dsb ishst" here, processes are being
+	 * terminated due to bus errors and segmentation violations. 
+	 */
+	pmap_invalidate_page(pmap, va);
+
 	return (mpte);
 }