Index: sys/boot/i386/libi386/biosdisk.c
===================================================================
--- sys/boot/i386/libi386/biosdisk.c	(revision 276757)
+++ sys/boot/i386/libi386/biosdisk.c	(working copy)
@@ -496,8 +496,9 @@
 
     /* Decide whether we have to bounce */
     if (VTOP(dest) >> 20 != 0 || (BD(dev).bd_unit < 0x80 &&
+	(VTOP(dest + blks * BD(dev).bd_sectorsize) >= 16384 * 1024 ||
 	(VTOP(dest) >> 16) != (VTOP(dest +
-	blks * BD(dev).bd_sectorsize) >> 16))) {
+	blks * BD(dev).bd_sectorsize) >> 16)))) {
 
 	/* 
 	 * There is a 64k physical boundary somewhere in the
Index: sys/boot/i386/libi386/biosmem.c
===================================================================
--- sys/boot/i386/libi386/biosmem.c	(revision 276757)
+++ sys/boot/i386/libi386/biosmem.c	(working copy)
@@ -32,6 +32,7 @@
  */
 #include <stand.h>
 #include <machine/pc/bios.h>
+#include "bootstrap.h"
 #include "libi386.h"
 #include "btxv86.h"
 
@@ -38,9 +39,20 @@
 vm_offset_t	memtop, memtop_copyin, high_heap_base;
 uint32_t	bios_basemem, bios_extmem, high_heap_size;
 
-static struct bios_smap smap;
+static struct bios_smap_xattr smap;
 
 /*
+ * Used to track which method was used to set BIOS memory
+ * regions.
+ */
+uint8_t b_bios_probed = 0;
+#define	B_BASEMEM_E820 0x1
+#define	B_BASEMEM_12 0x2
+#define	B_EXTMEM_E820 0x4
+#define	B_EXTMEM_E801 0x8
+#define	B_EXTMEM_8800 0x10
+
+/*
  * The minimum amount of memory to reserve in bios_extmem for the heap.
  */
 #define	HEAP_MIN	(3 * 1024 * 1024)
@@ -56,7 +68,7 @@
 	v86.ctl = V86_FLAGS;
 	v86.addr = 0x15;		/* int 0x15 function 0xe820*/
 	v86.eax = 0xe820;
-	v86.ecx = sizeof(struct bios_smap);
+	v86.ecx = sizeof(struct bios_smap_xattr);
 	v86.edx = SMAP_SIG;
 	v86.es = VTOPSEG(&smap);
 	v86.edi = VTOPOFF(&smap);
@@ -65,11 +77,17 @@
 	    break;
 	/* look for a low-memory segment that's large enough */
 	if ((smap.type == SMAP_TYPE_MEMORY) && (smap.base == 0) &&
-	    (smap.length >= (512 * 1024)))
+	    (smap.length >= (512 * 1024))) {
 	    bios_basemem = smap.length;
+	    b_bios_probed |= B_BASEMEM_E820;
+	    	
+	}
 	/* look for the first segment in 'extended' memory */
-	if ((smap.type == SMAP_TYPE_MEMORY) && (smap.base == 0x100000)) {
+	/* we need it to be at least 32MiB or -HEAD won't load */
+	if ((smap.type == SMAP_TYPE_MEMORY) && (smap.base == 0x100000) &&
+	    (smap.length >= (32 * 1024 * 1024))) {
 	    bios_extmem = smap.length;
+	    b_bios_probed |= B_EXTMEM_E820;
 	}
 
 	/*
@@ -100,6 +118,7 @@
 	v86int();
 	
 	bios_basemem = (v86.eax & 0xffff) * 1024;
+	b_bios_probed |= B_BASEMEM_12;
     }
 
     /* Fall back through several compatibility functions for extended memory */
@@ -109,7 +128,29 @@
 	v86.eax = 0xe801;
 	v86int();
 	if (!(V86_CY(v86.efl))) {
-	    bios_extmem = ((v86.ecx & 0xffff) + ((v86.edx & 0xffff) * 64)) * 1024;
+	    /*
+	     * Clear high_heap; it may end up overlapping
+	     * with the segment we're determining here.
+	     * Let the default "steal stuff from top of
+	     * bios_extmem" code below pick up on it.
+	     */
+	    high_heap_size = 0;
+	    high_heap_base = 0;
+	    /*
+	     * cx is the number of 1KiB blocks between 1..16MiB.
+	     * It can only be up to 0x3c00; if it's smaller then
+	     * there's a PC AT memory hole so we can't treat
+	     * it as contiguous.
+	     */
+	    bios_extmem = (v86.ecx & 0xffff) * 1024;
+	    if (bios_extmem == (1024 * 0x3c00))
+	        bios_extmem += (v86.edx & 0xffff) * 64 * 1024;
+
+	    /* truncate bios_extmem */
+	    if (bios_extmem > 0x3ff00000)
+	        bios_extmem = 0x3ff00000;
+
+	    b_bios_probed |= B_EXTMEM_E801;
 	}
     }
     if (bios_extmem == 0) {
@@ -118,6 +159,7 @@
 	v86.eax = 0x8800;
 	v86int();
 	bios_extmem = (v86.eax & 0xffff) * 1024;
+	b_bios_probed |= B_EXTMEM_8800;
     }
 
     /* Set memtop to actual top of memory */
@@ -133,3 +175,32 @@
 	high_heap_base = memtop - HEAP_MIN;
     }
 }    
+
+static int
+command_biosmem(int argc, char *argv[])
+{
+
+	printf("bios_basemem: 0x%llx\n", (unsigned long long) bios_basemem);
+	printf("bios_extmem: 0x%llx\n", (unsigned long long) bios_extmem);
+	printf("memtop: 0x%llx\n", (unsigned long long) memtop);
+	printf("high_heap_base: 0x%llx\n", (unsigned long long) high_heap_base);
+	printf("high_heap_size: 0x%llx\n", (unsigned long long) high_heap_size);
+	printf("b_bios_probed: 0x%02x ", (int) b_bios_probed);
+	if (b_bios_probed & B_BASEMEM_E820)
+		printf(" B_BASEMEM_E820");
+	if (b_bios_probed & B_BASEMEM_12)
+		printf(" B_BASEMEM_12");
+	if (b_bios_probed & B_EXTMEM_E820)
+		printf(" B_EXTMEM_E820");
+	if (b_bios_probed & B_EXTMEM_E801)
+		printf(" B_EXTMEM_E801");
+	if (b_bios_probed & B_EXTMEM_8800)
+		printf(" B_EXTMEM_8800");
+	printf("\n");
+
+	return (CMD_OK);
+}
+
+COMMAND_SET(smap, "biosmem", "show BIOS memory setup", command_biosmem);
+
+