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UEFI Memory V E820 Memory

I use the EFI STUB method to boot Fedora 17 directly from a UEFI shell without using GRUB. When I got a new Lenovo T430 laptop in July, I found that when I installed a UEFI shell and tried to boot Fedora 17, it simply hung and I had to power cycle the laptop. The problem turned out to be due to the way memory is reported to the Linux kernel by the laptop firmware.

Some background information first before I provide the solution. One of the most vital pieces of information that an operating system (OS) needs in order to initialize itself is a map of available RAM. The only practical way an OS could get that information up to recently on a PC was via the BIOS. E820 is a nickname that refers to the facility by which the BIOS of an x86-based computer system reports the memory map to an operating system or a boot loader.

The nickname comes from the fact that it is accessed via the BIOS INT 15h call, by setting the AX register to the value OxE820 (Query System Address Map function.) This function has been available on all PCs since 2002 and was available on most PCs for a long time before that. It reports which memory address ranges (both RAM and ROM) are usable and which are reserved for use only by the BIOS. E820 memory (see arch/x86/kernel/e820.c) is one of the first things looked for by a booting Linux kernel (see ../arch/i386/boot/setup.S.)

The idea of using E820 to query platform physical memory was fine while BIOS was the predominant platform firmware. With the arrival of UEFI firmware, things changed. A UEFI-based OS typically gets the platform physical memory map using the UEFI GetMemoryMap interface. This did not sit easily with many Linux kernel developers. According to Linus Torvalds in an email dated July 25th, 2006:

On Mon, 24 Jul 2006, Andrew Morton wrote:
>
> > This Patch add an efi e820 memory mapping.
> >
>
> Why?

EFI is this other Intel brain-damage (the first one being ACPI). It’s totally different from a normal BIOS, and was brought on by ia64, which never had a BIOS, of course.

Sadly, Apple bought into the whole “BIOS bad, EFI good” hype, so we now have x86 machines with EFI as the native boot protocol.

The original EFI code in the kernel basically duplicates all the BIOS interfaces (ie everything that looks at a memory map comes in two varieties: the normal and tested BIOS e820 variety, and the usually broken and hacked-up EFI memory map variety).

Translating the EFI memory map to e820 is very much the sane thing to do, and should have been done by ia64 in the first place. Sadly, EFI people (a) think that their stinking mess is better than a BIOS and (b) are historically ia64-only, so they didn’t do that, but went the “we’ll just duplicate everything using our inferior EFI interfaces” way.

Despite E820 being BIOS-specific, the Linux kernel continues to use the E820 map for the in-kernel representation of the memory address map under EFI as well. This caused (and seems to still cause) much pain and angst amongst kernel developers. For example, in a proposal in 2010 by Bill Richardson to “allow empty e820 map if EFI map will be provided later”, H Peter Anvin’s response was:

o! Bloody **** hell no!

This is yet another attempt at doing more of the wrong thing, which not
only will make it harder to push things that should be earlier in the
kernel there.

This was settled in 2007 — it is the boot loaders duty to provide a
memory map. The fact that we allowed a hack in to let the kernel itself
add additional ranges from EFI has proven to be an utter mistake, and
this is yet another example of it.

Vetoed in the extreme.

-hpa

The solution (hack), arrived at by the Linux kernel developers in 2009 after a number of false starts was to add a kernel command line option, add_efi_memmap – to tell the kernel to look at the EFI memory map and use it to fix up various entries in the E820 memory map.

From …/arch/xx86/platform/efi/efi.c:

static void __init do_add_efi_memmap(void)
{
   void *p;

   for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
       efi_memory_desc_t *md = p;
       unsigned long long start = md->phys_addr;
       unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
       int e820_type;

       switch (md->type) {
           case EFI_LOADER_CODE:
           case EFI_LOADER_DATA:
           case EFI_BOOT_SERVICES_CODE:
           case EFI_BOOT_SERVICES_DATA:
           case EFI_CONVENTIONAL_MEMORY:
               if (md->attribute & EFI_MEMORY_WB)
                   e820_type = E820_RAM;
               else
                   e820_type = E820_RESERVED;
               break;
           case EFI_ACPI_RECLAIM_MEMORY:
               e820_type = E820_ACPI;
               break;
           case EFI_ACPI_MEMORY_NVS:
               e820_type = E820_NVS;
               break;
           case EFI_UNUSABLE_MEMORY:
               e820_type = E820_UNUSABLE;
               break;
           default:
               /*
                * EFI_RESERVED_TYPE EFI_RUNTIME_SERVICES_CODE
                * EFI_RUNTIME_SERVICES_DATA EFI_MEMORY_MAPPED_IO
                * EFI_MEMORY_MAPPED_IO_PORT_SPACE EFI_PAL_CODE
                */
                e820_type = E820_RESERVED;
                break;
        }
        e820_add_region(start, size, e820_type);
    }
    sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
}


Whereas E820 was limited to 128 (E820MAX) memory regions due to the constrained space in the zeropage, EFI has no such limit. The do_add_efi_memmap function adds the memory regions reported by EFI to the kernel’s E820 map, modifies some entries and then sorts and removes overlaps and duplicates. See …/arch/x86/kernel/e820.c for more information.

Here is the source code for a simple UEFI command line utility to print out the the EFI memory regions:

//
//   Copyright (c) 2012  Finnbarr P. Murphy   All rights reserved.
//
//   License: BSD
//

#include <efi.h>
#include <efilib.h>

#define PAGE_SIZE 4096

const CHAR16 *memory_types[] = {
    L"EfiReservedMemoryType",
    L"EfiLoaderCode",
    L"EfiLoaderData",
    L"EfiBootServicesCode",
    L"EfiBootServicesData",
    L"EfiRuntimeServicesCode",
    L"EfiRuntimeServicesData",
    L"EfiConventionalMemory",
    L"EfiUnusableMemory",
    L"EfiACPIReclaimMemory",
    L"EfiACPIMemoryNVS",
    L"EfiMemoryMappedIO",
    L"EfiMemoryMappedIOPortSpace",
    L"EfiPalCode",
};


const CHAR16 *
memory_type_to_str(UINT32 type)
{
    if (type > sizeof(memory_types)/sizeof(CHAR16 *))
        return L"Unknown";

    return memory_types[type];
}

                 
EFI_STATUS
memory_map(EFI_MEMORY_DESCRIPTOR **map_buf, UINTN *map_size,
           UINTN *map_key, UINTN *desc_size, UINT32 *desc_version)
{
    EFI_STATUS err = EFI_SUCCESS;

    *map_size = sizeof(**map_buf) * 31;

get_map:
    *map_size += sizeof(**map_buf);

    err = uefi_call_wrapper(BS->AllocatePool, 3, EfiLoaderData, *map_size, (void **)map_buf);
    if (err != EFI_SUCCESS) {
        Print(L"ERROR: Failed to allocate pool for memory map");
        return err;
    }

    err = uefi_call_wrapper(BS->GetMemoryMap, 5, map_size, *map_buf, map_key, desc_size, desc_version);
    if (err != EFI_SUCCESS) {
        if (err == EFI_BUFFER_TOO_SMALL) {
            uefi_call_wrapper(BS->FreePool, 1, (void *)*map_buf);
            goto get_map;
        }
        Print(L"ERROR: Failed to get memory map");
    }
    return err;
}


EFI_STATUS 
print_memory_map(void)
{
    EFI_MEMORY_DESCRIPTOR *buf;
    UINTN desc_size;
    UINT32 desc_version;
    UINTN size, map_key, mapping_size;
    EFI_MEMORY_DESCRIPTOR *desc;
    EFI_STATUS err = EFI_SUCCESS;
    int i = 0;

    err = memory_map(&buf, &size, &map_key, &desc_size, &desc_version);
    if (err != EFI_SUCCESS)
        return err;

    Print(L"Memory Map Size: %d\n", size);
    Print(L"Map Key: %d\n", map_key);
    Print(L"Descriptor Version: %d\n", desc_version);
    Print(L"Descriptor Size: %d\n\n", desc_size);

    desc = buf;
    while ((void *)desc < (void *)buf + size) {
        mapping_size = desc->NumberOfPages * PAGE_SIZE;

        Print(L"[#%02d] Type: %s  Attr: 0x%x\n", i, memory_type_to_str(desc->Type), desc->Attribute);
        Print(L"      Phys: %016llx-%016llx\n", desc->PhysicalStart, desc->PhysicalStart + mapping_size);
        Print(L"      Virt: %016llx-%016llx\n\n", desc->VirtualStart, desc->VirtualStart + mapping_size);

        desc = (void *)desc + desc_size;
        i++;
    }

    uefi_call_wrapper(BS->FreePool, 1, buf);
    return err;
}


EFI_STATUS
efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *systab)
{
    InitializeLib(image, systab);

    print_memory_map();

    return EFI_SUCCESS;
}


You need the gnu_efi package installed in order to be able to compile the code. I have placed the above source code and a Makefile on GitHub.

Here is what this utility outputted on my Lenovo T430:

fs0:>efimemory
Memory Map Size: 2736
Map Key: 31803
Descriptor Version: 1
Descriptor Size: 48

[#00] Type: EfiBootServicesCode  Attr: 0xF
      Phys: 0000000000000000-0000000000001000
      Virt: 0000000000000000-0000000000001000

[#01] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 0000000000001000-000000000005B000
      Virt: 0000000000000000-000000000005A000

[#02] Type: EfiBootServicesData  Attr: 0xF
      Phys: 000000000005B000-000000000005C000
      Virt: 0000000000000000-0000000000001000

[#03] Type: EfiBootServicesCode  Attr: 0xF
      Phys: 000000000005C000-0000000000087000
      Virt: 0000000000000000-000000000002B000

[#04] Type: EfiBootServicesData  Attr: 0xF
      Phys: 0000000000087000-0000000000088000
      Virt: 0000000000000000-0000000000001000

[#05] Type: EfiBootServicesCode  Attr: 0xF
      Phys: 0000000000088000-0000000000090000
      Virt: 0000000000000000-0000000000008000

[#06] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 0000000000090000-00000000000A0000
      Virt: 0000000000000000-0000000000010000

[#07] Type: EfiBootServicesCode  Attr: 0xF
      Phys: 0000000000100000-0000000000110000
      Virt: 0000000000000000-0000000000010000

[#08] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 0000000000110000-0000000020000000
      Virt: 0000000000000000-000000001FEF0000

[#09] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 0000000020000000-0000000020200000
      Virt: 0000000000000000-0000000000200000

[#10] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 0000000020200000-0000000040004000
      Virt: 0000000000000000-000000001FE04000

[#11] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 0000000040004000-0000000040005000
      Virt: 0000000000000000-0000000000001000

[#12] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 0000000040005000-00000000D0489000
      Virt: 0000000000000000-0000000090484000

[#13] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D0489000-00000000D04A9000
      Virt: 0000000000000000-0000000000020000

[#14] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D04A9000-00000000D2AA2000
      Virt: 0000000000000000-00000000025F9000

[#15] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D2AA2000-00000000D2AB8000
      Virt: 0000000000000000-0000000000016000

[#16] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 00000000D2AB8000-00000000D2CBA000
      Virt: 0000000000000000-0000000000202000

[#17] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D2CBA000-00000000D3479000
      Virt: 0000000000000000-00000000007BF000

[#18] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D3479000-00000000D347D000
      Virt: 0000000000000000-0000000000004000

[#19] Type: EfiLoaderData  Attr: 0xF
      Phys: 00000000D347D000-00000000D348D000
      Virt: 0000000000000000-0000000000010000

[#20] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D348D000-00000000D3490000
      Virt: 0000000000000000-0000000000003000

[#21] Type: EfiLoaderData  Attr: 0xF
      Phys: 00000000D3490000-00000000D3492000
      Virt: 0000000000000000-0000000000002000

[#22] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D3492000-00000000D3497000
      Virt: 0000000000000000-0000000000005000

[#23] Type: EfiLoaderData  Attr: 0xF
      Phys: 00000000D3497000-00000000D34A6000
      Virt: 0000000000000000-000000000000F000

[#24] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D34A6000-00000000D398C000
      Virt: 0000000000000000-00000000004E6000

[#25] Type: EfiLoaderCode  Attr: 0xF
      Phys: 00000000D398C000-00000000D3A5A000
      Virt: 0000000000000000-00000000000CE000

[#26] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D3A5A000-00000000D4A76000
      Virt: 0000000000000000-000000000101C000

[#27] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D4A76000-00000000D55E4000
      Virt: 0000000000000000-0000000000B6E000

[#28] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D55E4000-00000000D570F000
      Virt: 0000000000000000-000000000012B000

[#29] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D570F000-00000000D5C8F000
      Virt: 0000000000000000-0000000000580000

[#30] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D5C8F000-00000000D5DBF000
      Virt: 0000000000000000-0000000000130000

[#31] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D5DBF000-00000000D617E000
      Virt: 0000000000000000-00000000003BF000

[#32] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D617E000-00000000D617F000
      Virt: 0000000000000000-0000000000001000

[#33] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D617F000-00000000D6180000
      Virt: 0000000000000000-0000000000001000

[#34] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D6180000-00000000D6188000
      Virt: 0000000000000000-0000000000008000

[#35] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000D6188000-00000000D7A5A000
      Virt: 0000000000000000-00000000018D2000

[#36] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 00000000D7A5A000-00000000D7C39000
      Virt: 0000000000000000-00000000001DF000

[#37] Type: EfiBootServicesCode  Attr: 0xF
      Phys: 00000000D7C39000-00000000D845A000
      Virt: 0000000000000000-0000000000821000

[#38] Type: EfiRuntimeServicesCode  Attr: 0xF
      Phys: 00000000D845A000-00000000D8505000
      Virt: 0000000000000000-00000000000AB000

[#39] Type: EfiRuntimeServicesCode  Attr: 0xF
      Phys: 00000000D8505000-00000000D865A000
      Virt: 0000000000000000-0000000000155000

[#40] Type: EfiRuntimeServicesData  Attr: 0xF
      Phys: 00000000D865A000-00000000D8BEB000
      Virt: 0000000000000000-0000000000591000

[#41] Type: EfiRuntimeServicesData  Attr: 0xF
      Phys: 00000000D8BEB000-00000000DA65A000
      Virt: 0000000000000000-0000000001A6F000

[#42] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 00000000DA65A000-00000000DAE35000
      Virt: 0000000000000000-00000000007DB000

[#43] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 00000000DAE35000-00000000DAE9B000
      Virt: 0000000000000000-0000000000066000

[#44] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 00000000DAE9B000-00000000DAE9D000
      Virt: 0000000000000000-0000000000002000

[#45] Type: EfiReservedMemoryType  Attr: 0xF
      Phys: 00000000DAE9D000-00000000DAE9F000
      Virt: 0000000000000000-0000000000002000

[#46] Type: EfiACPIMemoryNVS  Attr: 0xF
      Phys: 00000000DAE9F000-00000000DAEF6000
      Virt: 0000000000000000-0000000000057000

[#47] Type: EfiACPIMemoryNVS  Attr: 0xF
      Phys: 00000000DAEF6000-00000000DAF9F000
      Virt: 0000000000000000-00000000000A9000

[#48] Type: EfiACPIReclaimMemory  Attr: 0xF
      Phys: 00000000DAF9F000-00000000DAFDB000
      Virt: 0000000000000000-000000000003C000

[#49] Type: EfiACPIReclaimMemory  Attr: 0xF
      Phys: 00000000DAFDB000-00000000DAFFF000
      Virt: 0000000000000000-0000000000024000

[#50] Type: EfiBootServicesData  Attr: 0xF
      Phys: 00000000DAFFF000-00000000DB000000
      Virt: 0000000000000000-0000000000001000

[#51] Type: EfiConventionalMemory  Attr: 0xF
      Phys: 0000000100000000-000000021E600000
      Virt: 0000000000000000-000000011E600000

[#52] Type: EfiReservedMemoryType  Attr: 0x0
      Phys: 00000000000A0000-00000000000C0000
      Virt: 0000000000000000-0000000000020000

[#53] Type: EfiReservedMemoryType  Attr: 0x0
      Phys: 00000000DB000000-00000000DFA00000
      Virt: 0000000000000000-0000000004A00000

[#54] Type: EfiMemoryMappedIO  Attr: 0x1
      Phys: 00000000F80F8000-00000000F80F9000
      Virt: 0000000000000000-0000000000001000

[#55] Type: EfiMemoryMappedIO  Attr: 0x1
      Phys: 00000000FED1C000-00000000FED20000
      Virt: 0000000000000000-0000000000004000

[#56] Type: EfiReservedMemoryType  Attr: 0x0
      Phys: 000000021E600000-000000021E800000
      Virt: 0000000000000000-0000000000200000
fs0>

So back to my original problem. Why I was encountering this problem now for the first time and what was the solution or workaround? After all I have been using UEFI booting for a number of years and have been using the EFI STUB method of booting the kernel since it became available in the Linux kernel. It would appear that all the UEFI firmware I previously used had a CSM (Compatibility Support Module) that could have provided a suitable E820-style memory map to the kernel. Furthermore, until recently I was using either GRUB2 or Red Hat’s EFI-aware GRUB Legacy which both seem to provide an E820-style memory map to the kernel (however I have not checked the source code to ascertain.)

Once I understood the problem, the solution was simple – provide the additional kernel command line option, add_efi_memmap, on the kernel command line.

add_efi_memmap - Include EFI memory map of available physical RAM
                 
                 If the EFI memory map has additional entries not in the E820 map,
                 include those entries in the kernels memory map of available physical RAM 


Here is how I created a suitable UEFI BootXXXX variable containing this kernel option using efibootmgr:

# echo  " root=UUID=5716419d-0fe4-47a3-bed5-83aeb1c80a5a rd.md=0 rd.lvm=0 rd.dm=0 " \
        " KEYTABLE=us SYSFONT=True rd.luks=0 ro LANG=en_US.UTF-8 add_efi_memmap " \
        " rhgb quiet initrd=\initramfs.img" | iconv -f ascii -t ucs2 | 
  efibootmgr --create --gpt --label "Fedora 17 (EFISTUB)"  --loader vmlinuz.efi --disk /dev/sdb --append-binary-args -


In case you are wondering after looking at the above, I simply copy the latest initramfs-* and vmlinux-* to /boot/efi/initramfs and /boot/efi/vmlinux.efi respectively. I find this easier to do rather than delete and recreate the BootXXXX variable. I do not bother placing my Fedora kernel in a subdirectory such as \EFI\FEDORA\ in the ESP (EFI System Partition.) Furthermore the kernel options must be encoded as UCS2 instead of ASCII or UTF8 because that is what the UEFI specification calls for.

Here is the output from efibootmgr -v after adding the new boot variable.

# efibootmgr -v
BootCurrent: 001A
Timeout: 0 seconds
BootOrder: 001A,0019,0018,000A,0000,0001,0002,0003,0007,0008,0009,000B,000C,000D,000E,000F,0011,0010,0012
Boot0000  Setup	
Boot0001  Boot Menu	
Boot0002  Diagnostic Splash Screen	
Boot0003  Lenovo Diagnostics	
Boot0004  Startup Interrupt Menu	
Boot0005  ME Configuration Menu	
Boot0006  Rescue and Recovery	
Boot0007* USB CD	030a2400d23878bc820f604d8316c068ee79d25b86701296aa5a7848b66cd49dd3ba6a55
Boot0008* USB FDD	030a2400d23878bc820f604d8316c068ee79d25b6ff015a28830b543a8b8641009461e49
Boot0009* ATAPI CD0	030a2500d23878bc820f604d8316c068ee79d25baea2090adfde214e8b3a5e471856a35401
Boot000A* ATA HDD0	030a2500d23878bc820f604d8316c068ee79d25b91af625956449f41a7b91f4f892ab0f600
Boot000B* ATA HDD1	030a2500d23878bc820f604d8316c068ee79d25b91af625956449f41a7b91f4f892ab0f601
Boot000C* ATA HDD2	030a2500d23878bc820f604d8316c068ee79d25b91af625956449f41a7b91f4f892ab0f602
Boot000D* USB HDD	030a2400d23878bc820f604d8316c068ee79d25b33e821aaaf33bc4789bd419f88c50803
Boot000E* PCI LAN	030a2400d23878bc820f604d8316c068ee79d25b78a84aaf2b2afc4ea79cf5cc8f3d3803
Boot000F* ATAPI CD1	030a2500d23878bc820f604d8316c068ee79d25baea2090adfde214e8b3a5e471856a35404
Boot0010  Other CD	030a2500d23878bc820f604d8316c068ee79d25baea2090adfde214e8b3a5e471856a35406
Boot0011* ATA HDD3	030a2500d23878bc820f604d8316c068ee79d25b91af625956449f41a7b91f4f892ab0f604
Boot0012  Other HDD	030a2500d23878bc820f604d8316c068ee79d25b91af625956449f41a7b91f4f892ab0f606
Boot0013* IDER BOOT CDROM	ACPI(a0341d0,0)PCI(16,2)ATAPI(0,1,0)
Boot0014* IDER BOOT Floppy	ACPI(a0341d0,0)PCI(16,2)ATAPI(0,0,0)
Boot0015* ATA HDD	030a2400d23878bc820f604d8316c068ee79d25b91af625956449f41a7b91f4f892ab0f6
Boot0016* ATAPI CD:	030a2400d23878bc820f604d8316c068ee79d25baea2090adfde214e8b3a5e471856a354
Boot0017* PCI LAN	030a2400d23878bc820f604d8316c068ee79d25b78a84aaf2b2afc4ea79cf5cc8f3d3803
Boot0018* Fedora	HD(1,1000,200000,9e81061f-b31f-4a4b-993c-23047ef6ac57)File(\EFI\redhat\grub.efi)
Boot0019* UEFI Shell	HD(1,1000,200000,9e81061f-b31f-4a4b-993c-23047ef6ac57)File(\EFI\fpmurphy\shell.efi)
Boot001A* Fedora 17 (EFISTUB)	HD(1,1000,200000,9e81061f-b31f-4a4b-993c-23047ef6ac57)File(vmlinuz.efi) .r.o.o.t.=.U.U.I.D.=.5.7.1.6.4.1.9.d.-.0.f.e.4.-.4.7.a.3.-.b.e.d.5.-.8.3.a.e.b.1.c.8.0.a.5.a. .r.d...m.d.=.0. .r.d...l.v.m.=.0. .r.d...d.m.=.0. . .K.E.Y.T.A.B.L.E.=.u.s. .S.Y.S.F.O.N.T.=.T.r.u.e. .r.d...l.u.k.s.=.0. .r.o. .L.A.N.G.=.e.n._.U.S...U.T.F.-.8. .a.d.d._.e.f.i._.m.e.m.m.a.p. .r.h.g.b. .q.u.i.e.t. .i.n.i.t.r.d.=.\.i.n.i.t.r.a.m.f.s...i.m.g...


You can see lots of useful information about both the E820 and EFI memory regions using the dmesg utility. Here is the relevant output for Fedora 17 on my T430 laptop:

[    0.000000] Initializing cgroup subsys cpuset
[    0.000000] Initializing cgroup subsys cpu
[    0.000000] Linux version 3.5.4-2.fc17.x86_64 (mockbuild@) (gcc version 4.7.2 20120921 (Red Hat 4.7.2-2) (GCC) ) #1 SMP Wed Sep 26 21:58:50 UTC 2012
[    0.000000] Command line:  root=UUID=48c9b731-d284-436d-b152-39a62240813d rd.md=0 rd.lvm=0 rd.dm=0  KEYTABLE=us SYSFONT=True rd.luks=0 ro LANG=en_US.UTF-8 add_efi_memmap rhgb quiet initrd=\initramfs.img
[    0.000000] e820: BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000008ffff] usable
[    0.000000] BIOS-e820: [mem 0x0000000000090000-0x00000000000bffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000001fffffff] usable
[    0.000000] BIOS-e820: [mem 0x0000000020000000-0x00000000201fffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000020200000-0x0000000040003fff] usable
[    0.000000] BIOS-e820: [mem 0x0000000040004000-0x0000000040004fff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000040005000-0x00000000d1067fff] usable
[    0.000000] BIOS-e820: [mem 0x00000000d1068000-0x00000000d1269fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000d126a000-0x00000000d6a09fff] usable
[    0.000000] BIOS-e820: [mem 0x00000000d6a0a000-0x00000000dae9efff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000dae9f000-0x00000000daf9efff] ACPI NVS
[    0.000000] BIOS-e820: [mem 0x00000000daf9f000-0x00000000daffefff] ACPI data
[    0.000000] BIOS-e820: [mem 0x00000000dafff000-0x00000000daffffff] usable
[    0.000000] BIOS-e820: [mem 0x00000000db000000-0x00000000df9fffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000f80f8000-0x00000000f80f8fff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000fed1c000-0x00000000fed1ffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000021e5fffff] usable
[    0.000000] BIOS-e820: [mem 0x000000021e600000-0x000000021e7fffff] reserved
[    0.000000] NX (Execute Disable) protection: active
[    0.000000] efi: EFI v2.31 by Lenovo
[    0.000000] efi:  ACPI 2.0=0xdaffe014  ACPI=0xdaffe000  SMBIOS=0xdae9e000 
[    0.000000] efi: mem00: type=3, attr=0xf, range=[0x0000000000000000-0x0000000000001000) (0MB)
[    0.000000] efi: mem01: type=2, attr=0xf, range=[0x0000000000001000-0x0000000000008000) (0MB)
[    0.000000] efi: mem02: type=7, attr=0xf, range=[0x0000000000008000-0x000000000005a000) (0MB)
[    0.000000] efi: mem03: type=4, attr=0xf, range=[0x000000000005a000-0x000000000005c000) (0MB)
[    0.000000] efi: mem04: type=3, attr=0xf, range=[0x000000000005c000-0x0000000000087000) (0MB)
[    0.000000] efi: mem05: type=4, attr=0xf, range=[0x0000000000087000-0x0000000000088000) (0MB)
[    0.000000] efi: mem06: type=3, attr=0xf, range=[0x0000000000088000-0x0000000000090000) (0MB)
[    0.000000] efi: mem07: type=0, attr=0xf, range=[0x0000000000090000-0x00000000000a0000) (0MB)
[    0.000000] efi: mem08: type=3, attr=0xf, range=[0x0000000000100000-0x0000000000110000) (0MB)
[    0.000000] efi: mem09: type=7, attr=0xf, range=[0x0000000000110000-0x0000000001000000) (14MB)
[    0.000000] efi: mem10: type=2, attr=0xf, range=[0x0000000001000000-0x00000000023bb000) (19MB)
[    0.000000] efi: mem11: type=7, attr=0xf, range=[0x00000000023bb000-0x0000000020000000) (476MB)
[    0.000000] efi: mem12: type=0, attr=0xf, range=[0x0000000020000000-0x0000000020200000) (2MB)
[    0.000000] efi: mem13: type=7, attr=0xf, range=[0x0000000020200000-0x0000000040004000) (510MB)
[    0.000000] efi: mem14: type=0, attr=0xf, range=[0x0000000040004000-0x0000000040005000) (0MB)
[    0.000000] efi: mem15: type=7, attr=0xf, range=[0x0000000040005000-0x000000007efcf000) (1007MB)
[    0.000000] efi: mem16: type=2, attr=0xf, range=[0x000000007efcf000-0x0000000080000000) (16MB)
[    0.000000] efi: mem17: type=7, attr=0xf, range=[0x0000000080000000-0x00000000cea39000) (1258MB)
[    0.000000] efi: mem18: type=4, attr=0xf, range=[0x00000000cea39000-0x00000000cea59000) (0MB)
[    0.000000] efi: mem19: type=7, attr=0xf, range=[0x00000000cea59000-0x00000000d1052000) (37MB)
[    0.000000] efi: mem20: type=4, attr=0xf, range=[0x00000000d1052000-0x00000000d1068000) (0MB)
[    0.000000] efi: mem21: type=0, attr=0xf, range=[0x00000000d1068000-0x00000000d126a000) (2MB)
[    0.000000] efi: mem22: type=4, attr=0xf, range=[0x00000000d126a000-0x00000000d1a29000) (7MB)
[    0.000000] efi: mem23: type=7, attr=0xf, range=[0x00000000d1a29000-0x00000000d1a55000) (0MB)
[    0.000000] efi: mem24: type=2, attr=0xf, range=[0x00000000d1a55000-0x00000000d1a56000) (0MB)
[    0.000000] efi: mem25: type=7, attr=0xf, range=[0x00000000d1a56000-0x00000000d1b7a000) (1MB)
[    0.000000] efi: mem26: type=1, attr=0xf, range=[0x00000000d1b7a000-0x00000000d200a000) (4MB)
[    0.000000] efi: mem27: type=7, attr=0xf, range=[0x00000000d200a000-0x00000000d2f27000) (15MB)
[    0.000000] efi: mem28: type=4, attr=0xf, range=[0x00000000d2f27000-0x00000000d34d5000) (5MB)
[    0.000000] efi: mem29: type=7, attr=0xf, range=[0x00000000d34d5000-0x00000000d34ef000) (0MB)
[    0.000000] efi: mem30: type=4, attr=0xf, range=[0x00000000d34ef000-0x00000000d46b8000) (17MB)
[    0.000000] efi: mem31: type=7, attr=0xf, range=[0x00000000d46b8000-0x00000000d46ca000) (0MB)
[    0.000000] efi: mem32: type=4, attr=0xf, range=[0x00000000d46ca000-0x00000000d600a000) (25MB)
[    0.000000] efi: mem33: type=7, attr=0xf, range=[0x00000000d600a000-0x00000000d618c000) (1MB)
[    0.000000] efi: mem34: type=3, attr=0xf, range=[0x00000000d618c000-0x00000000d6a0a000) (8MB)
[    0.000000] efi: mem35: type=5, attr=0x800000000000000f, range=[0x00000000d6a0a000-0x00000000d6ab0000) (0MB)
[    0.000000] efi: mem36: type=5, attr=0x800000000000000f, range=[0x00000000d6ab0000-0x00000000d6c0a000) (1MB)
[    0.000000] efi: mem37: type=6, attr=0x800000000000000f, range=[0x00000000d6c0a000-0x00000000d77b3000) (11MB)
[    0.000000] efi: mem38: type=6, attr=0x800000000000000f, range=[0x00000000d77b3000-0x00000000da65a000) (46MB)
[    0.000000] efi: mem39: type=0, attr=0xf, range=[0x00000000da65a000-0x00000000dae35000) (7MB)
[    0.000000] efi: mem40: type=0, attr=0xf, range=[0x00000000dae35000-0x00000000dae9b000) (0MB)
[    0.000000] efi: mem41: type=0, attr=0xf, range=[0x00000000dae9b000-0x00000000dae9d000) (0MB)
[    0.000000] efi: mem42: type=0, attr=0xf, range=[0x00000000dae9d000-0x00000000dae9f000) (0MB)
[    0.000000] efi: mem43: type=10, attr=0xf, range=[0x00000000dae9f000-0x00000000daef6000) (0MB)
[    0.000000] efi: mem44: type=10, attr=0xf, range=[0x00000000daef6000-0x00000000daf9f000) (0MB)
[    0.000000] efi: mem45: type=9, attr=0xf, range=[0x00000000daf9f000-0x00000000dafda000) (0MB)
[    0.000000] efi: mem46: type=9, attr=0xf, range=[0x00000000dafda000-0x00000000dafff000) (0MB)
[    0.000000] efi: mem47: type=4, attr=0xf, range=[0x00000000dafff000-0x00000000db000000) (0MB)
[    0.000000] efi: mem48: type=7, attr=0xf, range=[0x0000000100000000-0x000000021e600000) (4582MB)
[    0.000000] efi: mem49: type=0, attr=0x0, range=[0x00000000000a0000-0x00000000000c0000) (0MB)
[    0.000000] efi: mem50: type=0, attr=0x0, range=[0x00000000db000000-0x00000000dfa00000) (74MB)
[    0.000000] efi: mem51: type=11, attr=0x8000000000000001, range=[0x00000000f80f8000-0x00000000f80f9000) (0MB)
[    0.000000] efi: mem52: type=11, attr=0x8000000000000001, range=[0x00000000fed1c000-0x00000000fed20000) (0MB)
[    0.000000] efi: mem53: type=0, attr=0x0, range=[0x000000021e600000-0x000000021e800000) (2MB)
[    0.000000] DMI 2.7 present.
[    0.000000] DMI: LENOVO 2342CTO/2342CTO, BIOS G1ET69WW (2.05 ) 09/12/2012
[    0.000000] e820: update [mem 0x00000000-0x0000ffff] usable ==> reserved
[    0.000000] e820: remove [mem 0x000a0000-0x000fffff] usable
[    0.000000] No AGP bridge found
[    0.000000] e820: last_pfn = 0x21e600 max_arch_pfn = 0x400000000
[    0.000000] MTRR default type: uncachable
[    0.000000] MTRR fixed ranges enabled:
[    0.000000]   00000-9FFFF write-back
[    0.000000]   A0000-BFFFF uncachable
[    0.000000]   C0000-FFFFF write-protect
[    0.000000] MTRR variable ranges enabled:
[    0.000000]   0 base 0FFC00000 mask FFFC00000 write-protect
[    0.000000]   1 base 000000000 mask F80000000 write-back
[    0.000000]   2 base 080000000 mask FC0000000 write-back
[    0.000000]   3 base 0C0000000 mask FE0000000 write-back
[    0.000000]   4 base 0DC000000 mask FFC000000 uncachable
[    0.000000]   5 base 0DB000000 mask FFF000000 uncachable
[    0.000000]   6 base 100000000 mask F00000000 write-back
[    0.000000]   7 base 200000000 mask FE0000000 write-back
[    0.000000]   8 base 21F000000 mask FFF000000 uncachable
[    0.000000]   9 base 21E800000 mask FFF800000 uncachable
[    0.000000] x86 PAT enabled: cpu 0, old 0x7040600070406, new 0x7010600070106
[    0.000000] e820: last_pfn = 0xdb000 max_arch_pfn = 0x400000000
[    0.000000] initial memory mapped: [mem 0x00000000-0x1fffffff]
[    0.000000] Base memory trampoline at [ffff880000054000] 54000 size 24576
[    0.000000] init_memory_mapping: [mem 0x00000000-0xdaffffff]
[    0.000000]  [mem 0x00000000-0xdaffffff] page 2M
[    0.000000] kernel direct mapping tables up to 0xdaffffff @ [mem 0x1f923000-0x1fffffff]
[    0.000000] init_memory_mapping: [mem 0x100000000-0x21e5fffff]


Well, by now you shold now have a fairly good understanding of the difference between E820 and EFI memory maps amd how to solve the problem of booting your Linux kernel if your particular UEFI implementation causes a problem in this area.

As an aside, I see no reason to use GRUB, Lilo or any other boot loader when you are on a UEFI-enabled platform. Typically, UEFI comes with its own boot manager that is capable of booting Windows, Linux, BSD and more. Moreover, your boot time is significantly faster when you eliminate the GRUB bootloader.

1 comment to UEFI Memory V E820 Memory

  • saskia

    Interesting that the solution is actually that hack which the kernel developer called an “utter mistake.” What option would he have preferred, I wonder?