vm: verbatim import of x15's physical page allocator

2 files changed, 915 insertions, 0 deletions

diff --git a/i386/i386at/biosmem.c b/i386/i386at/biosmem.c
new file mode 100644
index 0000000..f626df8
--- /dev/null
+++ b/i386/i386at/biosmem.c
@@ -0,0 +1,831 @@
+/*
+ * Copyright (c) 2010-2014 Richard Braun.
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <kern/assert.h>
+#include <kern/init.h>
+#include <kern/macros.h>
+#include <kern/panic.h>
+#include <kern/param.h>
+#include <kern/printk.h>
+#include <kern/stddef.h>
+#include <kern/stdint.h>
+#include <kern/string.h>
+#include <kern/types.h>
+#include <machine/biosmem.h>
+#include <machine/boot.h>
+#include <machine/cpu.h>
+#include <machine/elf.h>
+#include <machine/multiboot.h>
+#include <vm/vm_kmem.h>
+#include <vm/vm_page.h>
+
+/*
+ * Maximum number of entries in the BIOS memory map.
+ *
+ * Because of adjustments of overlapping ranges, the memory map can grow
+ * to twice this size.
+ */
+#define BIOSMEM_MAX_MAP_SIZE 128
+
+/*
+ * Memory range types.
+ */
+#define BIOSMEM_TYPE_AVAILABLE  1
+#define BIOSMEM_TYPE_RESERVED   2
+#define BIOSMEM_TYPE_ACPI       3
+#define BIOSMEM_TYPE_NVS        4
+#define BIOSMEM_TYPE_UNUSABLE   5
+#define BIOSMEM_TYPE_DISABLED   6
+
+/*
+ * Memory map entry.
+ */
+struct biosmem_map_entry {
+    uint64_t base_addr;
+    uint64_t length;
+    unsigned int type;
+};
+
+/*
+ * Contiguous block of physical memory.
+ *
+ * Tha "available" range records what has been passed to the VM system as
+ * available inside the segment.
+ */
+struct biosmem_segment {
+    phys_addr_t start;
+    phys_addr_t end;
+    phys_addr_t avail_start;
+    phys_addr_t avail_end;
+};
+
+/*
+ * Memory map built from the information passed by the boot loader.
+ *
+ * If the boot loader didn't pass a valid memory map, a simple map is built
+ * based on the mem_lower and mem_upper multiboot fields.
+ */
+static struct biosmem_map_entry biosmem_map[BIOSMEM_MAX_MAP_SIZE * 2]
+    __bootdata;
+static unsigned int biosmem_map_size __bootdata;
+
+/*
+ * Physical segment boundaries.
+ */
+static struct biosmem_segment biosmem_segments[VM_PAGE_MAX_SEGS] __bootdata;
+
+/*
+ * Boundaries of the simple bootstrap heap.
+ *
+ * This heap is located above BIOS memory.
+ */
+static uint32_t biosmem_heap_start __bootdata;
+static uint32_t biosmem_heap_cur __bootdata;
+static uint32_t biosmem_heap_end __bootdata;
+
+static char biosmem_panic_toobig_msg[] __bootdata
+    = "biosmem: too many memory map entries";
+static char biosmem_panic_setup_msg[] __bootdata
+    = "biosmem: unable to set up the early memory allocator";
+static char biosmem_panic_noseg_msg[] __bootdata
+    = "biosmem: unable to find any memory segment";
+static char biosmem_panic_inval_msg[] __bootdata
+    = "biosmem: attempt to allocate 0 page";
+static char biosmem_panic_nomem_msg[] __bootdata
+    = "biosmem: unable to allocate memory";
+
+static void __boot
+biosmem_map_build(const struct multiboot_raw_info *mbi)
+{
+    struct multiboot_raw_mmap_entry *mb_entry, *mb_end;
+    struct biosmem_map_entry *start, *entry, *end;
+    unsigned long addr;
+
+    addr = mbi->mmap_addr;
+    mb_entry = (struct multiboot_raw_mmap_entry *)addr;
+    mb_end = (struct multiboot_raw_mmap_entry *)(addr + mbi->mmap_length);
+    start = biosmem_map;
+    entry = start;
+    end = entry + BIOSMEM_MAX_MAP_SIZE;
+
+    while ((mb_entry < mb_end) && (entry < end)) {
+        entry->base_addr = mb_entry->base_addr;
+        entry->length = mb_entry->length;
+        entry->type = mb_entry->type;
+
+        mb_entry = (void *)mb_entry + sizeof(mb_entry->size) + mb_entry->size;
+        entry++;
+    }
+
+    biosmem_map_size = entry - start;
+}
+
+static void __boot
+biosmem_map_build_simple(const struct multiboot_raw_info *mbi)
+{
+    struct biosmem_map_entry *entry;
+
+    entry = biosmem_map;
+    entry->base_addr = 0;
+    entry->length = mbi->mem_lower << 10;
+    entry->type = BIOSMEM_TYPE_AVAILABLE;
+
+    entry++;
+    entry->base_addr = BIOSMEM_END;
+    entry->length = mbi->mem_upper << 10;
+    entry->type = BIOSMEM_TYPE_AVAILABLE;
+
+    biosmem_map_size = 2;
+}
+
+static int __boot
+biosmem_map_entry_is_invalid(const struct biosmem_map_entry *entry)
+{
+    return (entry->base_addr + entry->length) <= entry->base_addr;
+}
+
+static void __boot
+biosmem_map_filter(void)
+{
+    struct biosmem_map_entry *entry;
+    unsigned int i;
+
+    i = 0;
+
+    while (i < biosmem_map_size) {
+        entry = &biosmem_map[i];
+
+        if (biosmem_map_entry_is_invalid(entry)) {
+            biosmem_map_size--;
+            boot_memmove(entry, entry + 1,
+                         (biosmem_map_size - i) * sizeof(*entry));
+            continue;
+        }
+
+        i++;
+    }
+}
+
+static void __boot
+biosmem_map_sort(void)
+{
+    struct biosmem_map_entry tmp;
+    unsigned int i, j;
+
+    /*
+     * Simple insertion sort.
+     */
+    for (i = 1; i < biosmem_map_size; i++) {
+        tmp = biosmem_map[i];
+
+        for (j = i - 1; j < i; j--) {
+            if (biosmem_map[j].base_addr < tmp.base_addr)
+                break;
+
+            biosmem_map[j + 1] = biosmem_map[j];
+        }
+
+        biosmem_map[j + 1] = tmp;
+    }
+}
+
+static void __boot
+biosmem_map_adjust(void)
+{
+    struct biosmem_map_entry tmp, *a, *b, *first, *second;
+    uint64_t a_end, b_end, last_end;
+    unsigned int i, j, last_type;
+
+    biosmem_map_filter();
+
+    /*
+     * Resolve overlapping areas, giving priority to most restrictive
+     * (i.e. numerically higher) types.
+     */
+    for (i = 0; i < biosmem_map_size; i++) {
+        a = &biosmem_map[i];
+        a_end = a->base_addr + a->length;
+
+        j = i + 1;
+
+        while (j < biosmem_map_size) {
+            b = &biosmem_map[j];
+            b_end = b->base_addr + b->length;
+
+            if ((a->base_addr >= b_end) || (a_end <= b->base_addr)) {
+                j++;
+                continue;
+            }
+
+            if (a->base_addr < b->base_addr) {
+                first = a;
+                second = b;
+            } else {
+                first = b;
+                second = a;
+            }
+
+            if (a_end > b_end) {
+                last_end = a_end;
+                last_type = a->type;
+            } else {
+                last_end = b_end;
+                last_type = b->type;
+            }
+
+            tmp.base_addr = second->base_addr;
+            tmp.length = MIN(a_end, b_end) - tmp.base_addr;
+            tmp.type = MAX(a->type, b->type);
+            first->length = tmp.base_addr - first->base_addr;
+            second->base_addr += tmp.length;
+            second->length = last_end - second->base_addr;
+            second->type = last_type;
+
+            /*
+             * Filter out invalid entries.
+             */
+            if (biosmem_map_entry_is_invalid(a)
+                && biosmem_map_entry_is_invalid(b)) {
+                *a = tmp;
+                biosmem_map_size--;
+                memmove(b, b + 1, (biosmem_map_size - j) * sizeof(*b));
+                continue;
+            } else if (biosmem_map_entry_is_invalid(a)) {
+                *a = tmp;
+                j++;
+                continue;
+            } else if (biosmem_map_entry_is_invalid(b)) {
+                *b = tmp;
+                j++;
+                continue;
+            }
+
+            if (tmp.type == a->type)
+                first = a;
+            else if (tmp.type == b->type)
+                first = b;
+            else {
+
+                /*
+                 * If the overlapping area can't be merged with one of its
+                 * neighbors, it must be added as a new entry.
+                 */
+
+                if (biosmem_map_size >= ARRAY_SIZE(biosmem_map))
+                    boot_panic(biosmem_panic_toobig_msg);
+
+                biosmem_map[biosmem_map_size] = tmp;
+                biosmem_map_size++;
+                j++;
+                continue;
+            }
+
+            if (first->base_addr > tmp.base_addr)
+                first->base_addr = tmp.base_addr;
+
+            first->length += tmp.length;
+            j++;
+        }
+    }
+
+    biosmem_map_sort();
+}
+
+static int __boot
+biosmem_map_find_avail(phys_addr_t *phys_start, phys_addr_t *phys_end)
+{
+    const struct biosmem_map_entry *entry, *map_end;
+    phys_addr_t seg_start, seg_end;
+    uint64_t start, end;
+
+    seg_start = (phys_addr_t)-1;
+    seg_end = (phys_addr_t)-1;
+    map_end = biosmem_map + biosmem_map_size;
+
+    for (entry = biosmem_map; entry < map_end; entry++) {
+        if (entry->type != BIOSMEM_TYPE_AVAILABLE)
+            continue;
+
+        start = vm_page_round(entry->base_addr);
+
+        if (start >= *phys_end)
+            break;
+
+        end = vm_page_trunc(entry->base_addr + entry->length);
+
+        if ((start < end) && (start < *phys_end) && (end > *phys_start)) {
+            if (seg_start == (phys_addr_t)-1)
+                seg_start = start;
+
+            seg_end = end;
+        }
+    }
+
+    if ((seg_start == (phys_addr_t)-1) || (seg_end == (phys_addr_t)-1))
+        return -1;
+
+    if (seg_start > *phys_start)
+        *phys_start = seg_start;
+
+    if (seg_end < *phys_end)
+        *phys_end = seg_end;
+
+    return 0;
+}
+
+static void __boot
+biosmem_set_segment(unsigned int seg_index, phys_addr_t start, phys_addr_t end)
+{
+    biosmem_segments[seg_index].start = start;
+    biosmem_segments[seg_index].end = end;
+}
+
+static phys_addr_t __boot
+biosmem_segment_end(unsigned int seg_index)
+{
+    return biosmem_segments[seg_index].end;
+}
+
+static phys_addr_t __boot
+biosmem_segment_size(unsigned int seg_index)
+{
+    return biosmem_segments[seg_index].end - biosmem_segments[seg_index].start;
+}
+
+static void __boot
+biosmem_save_cmdline_sizes(struct multiboot_raw_info *mbi)
+{
+    struct multiboot_raw_module *mod;
+    uint32_t i;
+
+    if (mbi->flags & MULTIBOOT_LOADER_CMDLINE)
+        mbi->unused0 = boot_strlen((char *)(unsigned long)mbi->cmdline) + 1;
+
+    if (mbi->flags & MULTIBOOT_LOADER_MODULES) {
+        unsigned long addr;
+
+        addr = mbi->mods_addr;
+
+        for (i = 0; i < mbi->mods_count; i++) {
+            mod = (struct multiboot_raw_module *)addr + i;
+            mod->reserved = boot_strlen((char *)(unsigned long)mod->string) + 1;
+        }
+    }
+}
+
+static void __boot
+biosmem_find_boot_data_update(uint32_t min, uint32_t *start, uint32_t *end,
+                              uint32_t data_start, uint32_t data_end)
+{
+    if ((min <= data_start) && (data_start < *start)) {
+        *start = data_start;
+        *end = data_end;
+    }
+}
+
+/*
+ * Find the first boot data in the given range, and return their containing
+ * area (start address is returned directly, end address is returned in end).
+ * The following are considered boot data :
+ *  - the kernel
+ *  - the kernel command line
+ *  - the module table
+ *  - the modules
+ *  - the modules command lines
+ *  - the ELF section header table
+ *  - the ELF .shstrtab, .symtab and .strtab sections
+ *
+ * If no boot data was found, 0 is returned, and the end address isn't set.
+ */
+static uint32_t __boot
+biosmem_find_boot_data(const struct multiboot_raw_info *mbi, uint32_t min,
+                       uint32_t max, uint32_t *endp)
+{
+    struct multiboot_raw_module *mod;
+    struct elf_shdr *shdr;
+    uint32_t i, start, end = end;
+    unsigned long tmp;
+
+    start = max;
+
+    biosmem_find_boot_data_update(min, &start, &end, (unsigned long)&_boot,
+                                  BOOT_VTOP((unsigned long)&_end));
+
+    if ((mbi->flags & MULTIBOOT_LOADER_CMDLINE) && (mbi->cmdline != 0))
+        biosmem_find_boot_data_update(min, &start, &end, mbi->cmdline,
+                                      mbi->cmdline + mbi->unused0);
+
+    if (mbi->flags & MULTIBOOT_LOADER_MODULES) {
+        i = mbi->mods_count * sizeof(struct multiboot_raw_module);
+        biosmem_find_boot_data_update(min, &start, &end, mbi->mods_addr,
+                                      mbi->mods_addr + i);
+        tmp = mbi->mods_addr;
+
+        for (i = 0; i < mbi->mods_count; i++) {
+            mod = (struct multiboot_raw_module *)tmp + i;
+            biosmem_find_boot_data_update(min, &start, &end, mod->mod_start,
+                                          mod->mod_end);
+
+            if (mod->string != 0)
+                biosmem_find_boot_data_update(min, &start, &end, mod->string,
+                                              mod->string + mod->reserved);
+        }
+    }
+
+    if (mbi->flags & MULTIBOOT_LOADER_SHDR) {
+        tmp = mbi->shdr_num * mbi->shdr_size;
+        biosmem_find_boot_data_update(min, &start, &end, mbi->shdr_addr,
+                                      mbi->shdr_addr + tmp);
+        tmp = mbi->shdr_addr;
+
+        for (i = 0; i < mbi->shdr_num; i++) {
+            shdr = (struct elf_shdr *)(tmp + (i * mbi->shdr_size));
+
+            if ((shdr->type != ELF_SHT_SYMTAB)
+                && (shdr->type != ELF_SHT_STRTAB))
+                continue;
+
+            biosmem_find_boot_data_update(min, &start, &end, shdr->addr,
+                                          shdr->addr + shdr->size);
+        }
+    }
+
+    if (start == max)
+        return 0;
+
+    *endp = end;
+    return start;
+}
+
+static void __boot
+biosmem_setup_allocator(struct multiboot_raw_info *mbi)
+{
+    uint32_t heap_start, heap_end, max_heap_start, max_heap_end;
+    uint32_t mem_end, next;
+
+    /*
+     * Find some memory for the heap. Look for the largest unused area in
+     * upper memory, carefully avoiding all boot data.
+     */
+    mem_end = vm_page_trunc((mbi->mem_upper + 1024) << 10);
+
+#ifndef __LP64__
+    if (mem_end > VM_PAGE_DIRECTMAP_LIMIT)
+        mem_end = VM_PAGE_DIRECTMAP_LIMIT;
+#endif /* __LP64__ */
+
+    max_heap_start = 0;
+    max_heap_end = 0;
+    next = BIOSMEM_END;
+
+    do {
+        heap_start = next;
+        heap_end = biosmem_find_boot_data(mbi, heap_start, mem_end, &next);
+
+        if (heap_end == 0) {
+            heap_end = mem_end;
+            next = 0;
+        }
+
+        if ((heap_end - heap_start) > (max_heap_end - max_heap_start)) {
+            max_heap_start = heap_start;
+            max_heap_end = heap_end;
+        }
+    } while (next != 0);
+
+    max_heap_start = vm_page_round(max_heap_start);
+    max_heap_end = vm_page_trunc(max_heap_end);
+
+    if (max_heap_start >= max_heap_end)
+        boot_panic(biosmem_panic_setup_msg);
+
+    biosmem_heap_start = max_heap_start;
+    biosmem_heap_end = max_heap_end;
+    biosmem_heap_cur = biosmem_heap_end;
+}
+
+void __boot
+biosmem_bootstrap(struct multiboot_raw_info *mbi)
+{
+    phys_addr_t phys_start, phys_end;
+    int error;
+
+    if (mbi->flags & MULTIBOOT_LOADER_MMAP)
+        biosmem_map_build(mbi);
+    else
+        biosmem_map_build_simple(mbi);
+
+    biosmem_map_adjust();
+
+    phys_start = BIOSMEM_BASE;
+    phys_end = VM_PAGE_DMA_LIMIT;
+    error = biosmem_map_find_avail(&phys_start, &phys_end);
+
+    if (error)
+        boot_panic(biosmem_panic_noseg_msg);
+
+    biosmem_set_segment(VM_PAGE_SEG_DMA, phys_start, phys_end);
+
+    phys_start = VM_PAGE_DMA_LIMIT;
+#ifdef VM_PAGE_DMA32_LIMIT
+    phys_end = VM_PAGE_DMA32_LIMIT;
+    error = biosmem_map_find_avail(&phys_start, &phys_end);
+
+    if (error)
+        goto out;
+
+    biosmem_set_segment(VM_PAGE_SEG_DMA32, phys_start, phys_end);
+
+    phys_start = VM_PAGE_DMA32_LIMIT;
+#endif /* VM_PAGE_DMA32_LIMIT */
+    phys_end = VM_PAGE_DIRECTMAP_LIMIT;
+    error = biosmem_map_find_avail(&phys_start, &phys_end);
+
+    if (error)
+        goto out;
+
+    biosmem_set_segment(VM_PAGE_SEG_DIRECTMAP, phys_start, phys_end);
+
+    phys_start = VM_PAGE_DIRECTMAP_LIMIT;
+    phys_end = VM_PAGE_HIGHMEM_LIMIT;
+    error = biosmem_map_find_avail(&phys_start, &phys_end);
+
+    if (error)
+        goto out;
+
+    biosmem_set_segment(VM_PAGE_SEG_HIGHMEM, phys_start, phys_end);
+
+out:
+
+    /*
+     * The kernel and modules command lines will be memory mapped later
+     * during initialization. Their respective sizes must be saved.
+     */
+    biosmem_save_cmdline_sizes(mbi);
+    biosmem_setup_allocator(mbi);
+}
+
+void * __boot
+biosmem_bootalloc(unsigned int nr_pages)
+{
+    unsigned long addr, size;
+
+    size = vm_page_ptoa(nr_pages);
+
+    if (size == 0)
+        boot_panic(biosmem_panic_inval_msg);
+
+    /* Top-down allocation to avoid unnecessarily filling DMA segments */
+    addr = biosmem_heap_cur - size;
+
+    if ((addr < biosmem_heap_start) || (addr > biosmem_heap_cur))
+        boot_panic(biosmem_panic_nomem_msg);
+
+    biosmem_heap_cur = addr;
+    return boot_memset((void *)addr, 0, size);
+}
+
+phys_addr_t __boot
+biosmem_directmap_size(void)
+{
+    if (biosmem_segment_size(VM_PAGE_SEG_DIRECTMAP) != 0)
+        return biosmem_segment_end(VM_PAGE_SEG_DIRECTMAP);
+    else if (biosmem_segment_size(VM_PAGE_SEG_DMA32) != 0)
+        return biosmem_segment_end(VM_PAGE_SEG_DMA32);
+    else
+        return biosmem_segment_end(VM_PAGE_SEG_DMA);
+}
+
+static const char * __init
+biosmem_type_desc(unsigned int type)
+{
+    switch (type) {
+    case BIOSMEM_TYPE_AVAILABLE:
+        return "available";
+    case BIOSMEM_TYPE_RESERVED:
+        return "reserved";
+    case BIOSMEM_TYPE_ACPI:
+        return "ACPI";
+    case BIOSMEM_TYPE_NVS:
+        return "ACPI NVS";
+    case BIOSMEM_TYPE_UNUSABLE:
+        return "unusable";
+    default:
+        return "unknown (reserved)";
+    }
+}
+
+static void __init
+biosmem_map_show(void)
+{
+    const struct biosmem_map_entry *entry, *end;
+
+    printk("biosmem: physical memory map:\n");
+
+    for (entry = biosmem_map, end = entry + biosmem_map_size;
+         entry < end;
+         entry++)
+        printk("biosmem: %018llx:%018llx, %s\n", entry->base_addr,
+               entry->base_addr + entry->length,
+               biosmem_type_desc(entry->type));
+
+    printk("biosmem: heap: %x-%x\n", biosmem_heap_start, biosmem_heap_end);
+}
+
+static void __init
+biosmem_load_segment(struct biosmem_segment *seg, uint64_t max_phys_end,
+                     phys_addr_t phys_start, phys_addr_t phys_end,
+                     phys_addr_t avail_start, phys_addr_t avail_end)
+{
+    unsigned int seg_index;
+
+    seg_index = seg - biosmem_segments;
+
+    if (phys_end > max_phys_end) {
+        if (max_phys_end <= phys_start) {
+            printk("biosmem: warning: segment %s physically unreachable, "
+                   "not loaded\n", vm_page_seg_name(seg_index));
+            return;
+        }
+
+        printk("biosmem: warning: segment %s truncated to %#llx\n",
+               vm_page_seg_name(seg_index), max_phys_end);
+        phys_end = max_phys_end;
+    }
+
+    if ((avail_start < phys_start) || (avail_start > phys_end))
+        avail_start = phys_start;
+
+    if ((avail_end < phys_start) || (avail_end > phys_end))
+        avail_end = phys_end;
+
+    seg->avail_start = avail_start;
+    seg->avail_end = avail_end;
+    vm_page_load(seg_index, phys_start, phys_end, avail_start, avail_end);
+}
+
+void __init
+biosmem_setup(void)
+{
+    uint64_t max_phys_end;
+    struct biosmem_segment *seg;
+    struct cpu *cpu;
+    unsigned int i;
+
+    biosmem_map_show();
+
+    cpu = cpu_current();
+    max_phys_end = (cpu->phys_addr_width == 0)
+                   ? (uint64_t)-1
+                   : (uint64_t)1 << cpu->phys_addr_width;
+
+    for (i = 0; i < ARRAY_SIZE(biosmem_segments); i++) {
+        if (biosmem_segment_size(i) == 0)
+            break;
+
+        seg = &biosmem_segments[i];
+        biosmem_load_segment(seg, max_phys_end, seg->start, seg->end,
+                             biosmem_heap_start, biosmem_heap_cur);
+    }
+}
+
+static void __init
+biosmem_free_usable_range(phys_addr_t start, phys_addr_t end)
+{
+    struct vm_page *page;
+
+    printk("biosmem: release to vm_page: %llx-%llx (%lluk)\n",
+           (unsigned long long)start, (unsigned long long)end,
+           (unsigned long long)((end - start) >> 10));
+
+    while (start < end) {
+        page = vm_page_lookup(start);
+        assert(page != NULL);
+        vm_page_manage(page);
+        start += PAGE_SIZE;
+    }
+}
+
+static void __init
+biosmem_free_usable_update_start(phys_addr_t *start, phys_addr_t res_start,
+                                 phys_addr_t res_end)
+{
+    if ((*start >= res_start) && (*start < res_end))
+        *start = res_end;
+}
+
+static phys_addr_t __init
+biosmem_free_usable_start(phys_addr_t start)
+{
+    const struct biosmem_segment *seg;
+    unsigned int i;
+
+    biosmem_free_usable_update_start(&start, (unsigned long)&_boot,
+                                     BOOT_VTOP((unsigned long)&_end));
+    biosmem_free_usable_update_start(&start, biosmem_heap_start,
+                                     biosmem_heap_end);
+
+    for (i = 0; i < ARRAY_SIZE(biosmem_segments); i++) {
+        seg = &biosmem_segments[i];
+        biosmem_free_usable_update_start(&start, seg->avail_start,
+                                         seg->avail_end);
+    }
+
+    return start;
+}
+
+static int __init
+biosmem_free_usable_reserved(phys_addr_t addr)
+{
+    const struct biosmem_segment *seg;
+    unsigned int i;
+
+    if ((addr >= (unsigned long)&_boot)
+        && (addr < BOOT_VTOP((unsigned long)&_end)))
+        return 1;
+
+    if ((addr >= biosmem_heap_start) && (addr < biosmem_heap_end))
+        return 1;
+
+    for (i = 0; i < ARRAY_SIZE(biosmem_segments); i++) {
+        seg = &biosmem_segments[i];
+
+        if ((addr >= seg->avail_start) && (addr < seg->avail_end))
+            return 1;
+    }
+
+    return 0;
+}
+
+static phys_addr_t __init
+biosmem_free_usable_end(phys_addr_t start, phys_addr_t entry_end)
+{
+    while (start < entry_end) {
+        if (biosmem_free_usable_reserved(start))
+            break;
+
+        start += PAGE_SIZE;
+    }
+
+    return start;
+}
+
+static void __init
+biosmem_free_usable_entry(phys_addr_t start, phys_addr_t end)
+{
+    phys_addr_t entry_end;
+
+    entry_end = end;
+
+    for (;;) {
+        start = biosmem_free_usable_start(start);
+
+        if (start >= entry_end)
+            return;
+
+        end = biosmem_free_usable_end(start, entry_end);
+        biosmem_free_usable_range(start, end);
+        start = end;
+    }
+}
+
+void __init
+biosmem_free_usable(void)
+{
+    struct biosmem_map_entry *entry;
+    uint64_t start, end;
+    unsigned int i;
+
+    for (i = 0; i < biosmem_map_size; i++) {
+        entry = &biosmem_map[i];
+
+        if (entry->type != BIOSMEM_TYPE_AVAILABLE)
+            continue;
+
+        start = vm_page_round(entry->base_addr);
+
+        if (start >= VM_PAGE_HIGHMEM_LIMIT)
+            break;
+
+        end = vm_page_trunc(entry->base_addr + entry->length);
+
+        if (start < BIOSMEM_BASE)
+            start = BIOSMEM_BASE;
+
+        biosmem_free_usable_entry(start, end);
+    }
+}
diff --git a/i386/i386at/biosmem.h b/i386/i386at/biosmem.h
new file mode 100644
index 0000000..b32e027
--- /dev/null
+++ b/i386/i386at/biosmem.h
@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2010-2014 Richard Braun.
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _X86_BIOSMEM_H
+#define _X86_BIOSMEM_H
+
+#include <kern/types.h>
+#include <machine/multiboot.h>
+
+/*
+ * Address where the address of the Extended BIOS Data Area segment can be
+ * found.
+ */
+#define BIOSMEM_EBDA_PTR 0x40e
+
+/*
+ * Significant low memory addresses.
+ *
+ * The first 64 KiB are reserved for various reasons (e.g. to preserve BIOS
+ * data and to work around data corruption on some hardware).
+ */
+#define BIOSMEM_BASE        0x010000
+#define BIOSMEM_BASE_END    0x0a0000
+#define BIOSMEM_EXT_ROM     0x0e0000
+#define BIOSMEM_ROM         0x0f0000
+#define BIOSMEM_END         0x100000
+
+/*
+ * Early initialization of the biosmem module.
+ *
+ * This function processes the given multiboot data for BIOS-provided
+ * memory information, and sets up a bootstrap physical page allocator.
+ *
+ * It is called before paging is enabled.
+ */
+void biosmem_bootstrap(struct multiboot_raw_info *mbi);
+
+/*
+ * Allocate contiguous physical pages during bootstrap.
+ *
+ * This function is called before paging is enabled. It should only be used
+ * to allocate initial page table pages. Those pages are later loaded into
+ * the VM system (as reserved pages) which means they can be freed like other
+ * regular pages. Users should fix up the type of those pages once the VM
+ * system is initialized.
+ */
+void * biosmem_bootalloc(unsigned int nr_pages);
+
+/*
+ * Return the amount of physical memory that can be directly mapped.
+ *
+ * This includes the size of both the DMA/DMA32 and DIRECTMAP segments.
+ */
+phys_addr_t biosmem_directmap_size(void);
+
+/*
+ * Set up physical memory based on the information obtained during bootstrap
+ * and load it in the VM system.
+ */
+void biosmem_setup(void);
+
+/*
+ * Free all usable memory.
+ *
+ * This includes ranges that weren't part of the bootstrap allocator initial
+ * heap, e.g. because they contained boot data.
+ */
+void biosmem_free_usable(void);
+
+#endif /* _X86_BIOSMEM_H */