svn commit: r354792 - head/sys/arm64/arm64

[Alan Cox]

Author: alc
Date: Sun Nov 17 17:38:53 2019
New Revision: 354792
URL: https://svnweb.freebsd.org/changeset/base/354792

Log:
  Achieve two goals at once: (1) Avoid an unnecessary broadcast TLB
  invalidation in pmap_remove_all(). (2) Prevent an "invalid ASID" assertion
  failure in pmap_remove_all().
  
  The architecture definition specifies that the TLB will not cache mappings
  that don't have the "AF" bit set, so pmap_remove_all() needn't issue a TLB
  invalidation for mappings that don't have the "AF" bit set.
  
  We allocate ASIDs lazily.  Specifically, we don't allocate an ASID for a
  pmap until we are activating it.  Now, consider what happens on a fork().
  Before we activate the child's pmap, we use pmap_copy() to copy mappings
  from the parent's pmap to the child's.  These new mappings have their "AF"
  bits cleared.  Suppose that the page daemon decides to reclaim a page that
  underlies one of these new mappings.  Previously, the pmap_invalidate_page()
  performed by pmap_remove_all() on a mapping in the child's pmap would fail
  an assertion because that pmap hasn't yet been assigned an ASID.  However,
  we don't need to issue a TLB invalidation for such mappings because they
  can't possibly be cached in the TLB.
  
  Reported by:	bob prohaska <fbsd at www.zefox.net>
  Reviewed by:	markj
  MFC after:	1 week
  X-MFC-before:	r354286
  Differential Revision:	https://reviews.freebsd.org/D22388

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

Modified: head/sys/arm64/arm64/pmap.c
==============================================================================
--- head/sys/arm64/arm64/pmap.c	Sun Nov 17 14:54:43 2019	(r354791)
+++ head/sys/arm64/arm64/pmap.c	Sun Nov 17 17:38:53 2019	(r354792)
@@ -2879,11 +2879,12 @@ retry:
 
 		pte = pmap_l2_to_l3(pde, pv->pv_va);
 		tpte = pmap_load_clear(pte);
-		pmap_invalidate_page(pmap, pv->pv_va);
 		if (tpte & ATTR_SW_WIRED)
 			pmap->pm_stats.wired_count--;
-		if ((tpte & ATTR_AF) != 0)
+		if ((tpte & ATTR_AF) != 0) {
+			pmap_invalidate_page(pmap, pv->pv_va);
 			vm_page_aflag_set(m, PGA_REFERENCED);
+		}
 
 		/*
 		 * Update the vm_page_t clean and reference bits.