[pcbios] Restrict external memory allocations to the low 4GB

When running the 64-bit BIOS version of iPXE, restrict external memory
allocations to the low 4GB to ensure that allocations (such as for
initrds) fall within our identity-mapped memory region, and will be
accessible to the potentially 32-bit operating system.

Move largest_memblock() back to memtop_umalloc.c, since this change
imposes a restriction that applies only to BIOS builds.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/x86/interface/pcbios/memtop_umalloc.c

@@ -38,6 +38,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/memblock.h>
 #include <ipxe/umalloc.h>
 
+/** Maximum usable address for external allocated memory */
+#define EM_MAX_ADDRESS 0xffffffffUL
+
 /** Alignment of external allocated memory */
 #define EM_ALIGN ( 4 * 1024 )
 
@@ -61,6 +64,56 @@ static userptr_t bottom = UNULL;
 /** Remaining space on heap */
 static size_t heap_size;
 
+/**
+ * Find largest usable memory region
+ *
+ * @ret start		Start of region
+ * @ret len		Length of region
+ */
+size_t largest_memblock ( userptr_t *start ) {
+	struct memory_map memmap;
+	struct memory_region *region;
+	physaddr_t max = EM_MAX_ADDRESS;
+	physaddr_t region_start;
+	physaddr_t region_end;
+	size_t region_len;
+	unsigned int i;
+	size_t len = 0;
+
+	/* Avoid returning uninitialised data on error */
+	*start = UNULL;
+
+	/* Scan through all memory regions */
+	get_memmap ( &memmap );
+	for ( i = 0 ; i < memmap.count ; i++ ) {
+		region = &memmap.regions[i];
+		DBG ( "Considering [%llx,%llx)\n", region->start, region->end );
+
+		/* Truncate block to maximum physical address */
+		if ( region->start > max ) {
+			DBG ( "...starts after maximum address %lx\n", max );
+			continue;
+		}
+		region_start = region->start;
+		if ( region->end > max ) {
+			DBG ( "...end truncated to maximum address %lx\n", max);
+			region_end = 0; /* =max, given the wraparound */
+		} else {
+			region_end = region->end;
+		}
+		region_len = ( region_end - region_start );
+
+		/* Use largest block */
+		if ( region_len > len ) {
+			DBG ( "...new best block found\n" );
+			*start = phys_to_user ( region_start );
+			len = region_len;
+		}
+	}
+
+	return len;
+}
+
 /**
  * Initialise external heap
  *

src/core/memblock.c

@@ -1,85 +0,0 @@
-/*
- * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License as
- * published by the Free Software Foundation; either version 2 of the
- * License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
- * General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
- * 02110-1301, USA.
- *
- * You can also choose to distribute this program under the terms of
- * the Unmodified Binary Distribution Licence (as given in the file
- * COPYING.UBDL), provided that you have satisfied its requirements.
- */
-
-FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
-
-/** @file
- *
- * Largest memory block
- *
- */
-
-#include <stdint.h>
-#include <ipxe/uaccess.h>
-#include <ipxe/io.h>
-#include <ipxe/memblock.h>
-
-/**
- * Find largest usable memory region
- *
- * @ret start		Start of region
- * @ret len		Length of region
- */
-size_t largest_memblock ( userptr_t *start ) {
-	struct memory_map memmap;
-	struct memory_region *region;
-	physaddr_t max = ~( ( physaddr_t ) 0 );
-	physaddr_t region_start;
-	physaddr_t region_end;
-	size_t region_len;
-	unsigned int i;
-	size_t len = 0;
-
-	/* Avoid returning uninitialised data on error */
-	*start = UNULL;
-
-	/* Scan through all memory regions */
-	get_memmap ( &memmap );
-	for ( i = 0 ; i < memmap.count ; i++ ) {
-		region = &memmap.regions[i];
-		DBG ( "Considering [%llx,%llx)\n", region->start, region->end );
-
-		/* Truncate block to maximum physical address */
-		if ( region->start > max ) {
-			DBG ( "...starts after maximum address %lx\n", max );
-			continue;
-		}
-		region_start = region->start;
-		if ( region->end > max ) {
-			DBG ( "...end truncated to maximum address %lx\n", max);
-			region_end = 0; /* =max, given the wraparound */
-		} else {
-			region_end = region->end;
-		}
-		region_len = ( region_end - region_start );
-
-		/* Use largest block */
-		if ( region_len > len ) {
-			DBG ( "...new best block found\n" );
-			*start = phys_to_user ( region_start );
-			len = region_len;
-		}
-	}
-
-	return len;
-}