svn commit: r334799 - head/sys/amd64/amd64

[Konstantin Belousov]

Author: kib
Date: Thu Jun  7 17:04:34 2018
New Revision: 334799
URL: https://svnweb.freebsd.org/changeset/base/334799

Log:
  Account for dmap limit when selecting the pages for the bootstrap
  pagetables.
  
  physmap[] can be inconsistent with the physical memory limit due to
  buggy bios, or to the hw.physmem tunable. Since bootstrap pagetables
  are initialized by accesses through the DMAP, we must ensure that DMAP
  really cover the selected pages. This is only relevant when machine
  has less than 4G RAM and buggy BIOS, which is the combination on Acer
  Chromebook 720.
  
  The call to mp_bootaddress() is moved later to have Maxmem initialized.
  
  An alternative could be to always cover 4G for DMAP, but this change
  seems to be simpler.
  
  Reported and tested by:	grembo
  Reviewed by:	royger
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week
  Differential revision:	https://reviews.freebsd.org/D15675

Modified:
  head/sys/amd64/amd64/machdep.c
  head/sys/amd64/amd64/mp_machdep.c

Modified: head/sys/amd64/amd64/machdep.c
==============================================================================
--- head/sys/amd64/amd64/machdep.c	Thu Jun  7 16:35:09 2018	(r334798)
+++ head/sys/amd64/amd64/machdep.c	Thu Jun  7 17:04:34 2018	(r334799)
@@ -1248,15 +1248,6 @@ getmemsize(caddr_t kmdp, u_int64_t first)
 	}
 
 	/*
-	 * Make hole for "AP -> long mode" bootstrap code.  The
-	 * mp_bootaddress vector is only available when the kernel
-	 * is configured to support APs and APs for the system start
-	 * in real mode mode (e.g. SMP bare metal).
-	 */
-	if (init_ops.mp_bootaddress)
-		init_ops.mp_bootaddress(physmap, &physmap_idx);
-
-	/*
 	 * Maxmem isn't the "maximum memory", it's one larger than the
 	 * highest page of the physical address space.  It should be
 	 * called something like "Maxphyspage".  We may adjust this
@@ -1293,6 +1284,15 @@ getmemsize(caddr_t kmdp, u_int64_t first)
 	if (atop(physmap[physmap_idx + 1]) != Maxmem &&
 	    (boothowto & RB_VERBOSE))
 		printf("Physical memory use set to %ldK\n", Maxmem * 4);
+
+	/*
+	 * Make hole for "AP -> long mode" bootstrap code.  The
+	 * mp_bootaddress vector is only available when the kernel
+	 * is configured to support APs and APs for the system start
+	 * in real mode mode (e.g. SMP bare metal).
+	 */
+	if (init_ops.mp_bootaddress)
+		init_ops.mp_bootaddress(physmap, &physmap_idx);
 
 	/* call pmap initialization to make new kernel address space */
 	pmap_bootstrap(&first);

Modified: head/sys/amd64/amd64/mp_machdep.c
==============================================================================
--- head/sys/amd64/amd64/mp_machdep.c	Thu Jun  7 16:35:09 2018	(r334798)
+++ head/sys/amd64/amd64/mp_machdep.c	Thu Jun  7 17:04:34 2018	(r334799)
@@ -113,12 +113,16 @@ mp_bootaddress(vm_paddr_t *physmap, unsigned int *phys
 	allocated = false;
 	for (i = *physmap_idx; i <= *physmap_idx; i -= 2) {
 		/*
-		 * Find a memory region big enough below the 4GB boundary to
-		 * store the initial page tables. Note that it needs to be
-		 * aligned to a page boundary.
+		 * Find a memory region big enough below the 4GB
+		 * boundary to store the initial page tables.  Region
+		 * must be mapped by the direct map.
+		 *
+		 * Note that it needs to be aligned to a page
+		 * boundary.
 		 */
-		if (physmap[i] >= GiB(4) ||
-		    (physmap[i + 1] - round_page(physmap[i])) < (PAGE_SIZE * 3))
+		if (physmap[i] >= GiB(4) || physmap[i + 1] -
+		    round_page(physmap[i]) < PAGE_SIZE * 3 ||
+		    physmap[i + 1] > Maxmem)
 			continue;
 
 		allocated = true;