svn commit: r348306 - head/sys/amd64/amd64

[Konstantin Belousov]

Author: kib
Date: Mon May 27 15:21:26 2019
New Revision: 348306
URL: https://svnweb.freebsd.org/changeset/base/348306

Log:
  Correct some inconsistencies in the earliest created kernel page
  tables which affect demotion.
  
  The last last-level page table under 2M mappings below KERNend was
  only partially initialized.  When that page was used as the hardware
  page table for demotion of the 2M mapping, the result was not
  consistent.  Since pmap_demote_pde() is switched to use PG_PROMOTED as
  the test for the validity of the saved last level page table page, we
  can keep page table pages zero-initialized instead.  Demotion would
  fill them as needed.
  
  Only map the created page tables beyond KERNend, there is no need to
  pre-promote PTmap after KERNend, because the extra mapping is not used.
  
  Only round up *firstaddr to 2M boundary when it is below rounded
  KERNend.  Sometimes the allocpages() calls advance *firstaddr past the
  end of the last 2MB page mapping. In that case, this conditional
  avoids wasting an average of 1MB of physical memory.
  
  Update comments to explain action in more clean and direct language.
  
  Reported and tested by:	pho
  In collaboration with:	alc
  Sponsored by:	The FreeBSD Foundation (kib)
  MFC after:	1 week
  Differential revision:	https://reviews.freebsd.org/D20380

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

Modified: head/sys/amd64/amd64/pmap.c
==============================================================================
--- head/sys/amd64/amd64/pmap.c	Mon May 27 13:14:22 2019	(r348305)
+++ head/sys/amd64/amd64/pmap.c	Mon May 27 15:21:26 2019	(r348306)
@@ -1338,7 +1338,6 @@ static void
 create_pagetables(vm_paddr_t *firstaddr)
 {
 	int i, j, ndm1g, nkpdpe, nkdmpde;
-	pt_entry_t *pt_p;
 	pd_entry_t *pd_p;
 	pdp_entry_t *pdp_p;
 	pml4_entry_t *p4_p;
@@ -1399,20 +1398,21 @@ create_pagetables(vm_paddr_t *firstaddr)
 	KPTphys = allocpages(firstaddr, nkpt);
 	KPDphys = allocpages(firstaddr, nkpdpe);
 
-	/* Fill in the underlying page table pages */
-	/* XXX not fully used, underneath 2M pages */
-	pt_p = (pt_entry_t *)KPTphys;
-	for (i = 0; ptoa(i) < *firstaddr; i++)
-		pt_p[i] = ptoa(i) | X86_PG_V | pg_g | bootaddr_rwx(ptoa(i));
-
-	/* Now map the page tables at their location within PTmap */
+	/*
+	 * Connect the zero-filled PT pages to their PD entries.  This
+	 * implicitly maps the PT pages at their correct locations within
+	 * the PTmap.
+	 */
 	pd_p = (pd_entry_t *)KPDphys;
 	for (i = 0; i < nkpt; i++)
 		pd_p[i] = (KPTphys + ptoa(i)) | X86_PG_RW | X86_PG_V;
 
-	/* Map from zero to end of allocations under 2M pages */
-	/* This replaces some of the KPTphys entries above */
-	for (i = 0; (i << PDRSHIFT) < *firstaddr; i++)
+	/*
+	 * Map from physical address zero to the end of loader preallocated
+	 * memory using 2MB pages.  This replaces some of the PD entries
+	 * created above.
+	 */
+	for (i = 0; (i << PDRSHIFT) < KERNend; i++)
 		/* Preset PG_M and PG_A because demotion expects it. */
 		pd_p[i] = (i << PDRSHIFT) | X86_PG_V | PG_PS | pg_g |
 		    X86_PG_M | X86_PG_A | bootaddr_rwx(i << PDRSHIFT);
@@ -1422,7 +1422,8 @@ create_pagetables(vm_paddr_t *firstaddr)
 	 * to record the physical blocks we've actually mapped into kernel
 	 * virtual address space.
 	 */
-	*firstaddr = round_2mpage(*firstaddr);
+	if (*firstaddr < round_2mpage(KERNend))
+		*firstaddr = round_2mpage(KERNend);
 
 	/* And connect up the PD to the PDP (leaving room for L4 pages) */
 	pdp_p = (pdp_entry_t *)(KPDPphys + ptoa(KPML4I - KPML4BASE));
@@ -1529,7 +1530,10 @@ pmap_bootstrap(vm_paddr_t *firstaddr)
 	 */
 	vm_phys_add_seg(KPTphys, KPTphys + ptoa(nkpt));
 
-	virtual_avail = (vm_offset_t) KERNBASE + *firstaddr;
+	/*
+	 * Account for the virtual addresses mapped by create_pagetables().
+	 */
+	virtual_avail = (vm_offset_t)KERNBASE + round_2mpage(KERNend);
 	virtual_end = VM_MAX_KERNEL_ADDRESS;
 
 	/*