15.3. UEFI GetMemoryMap() Boot Services Function¶
EFI enabled systems use the UEFI GetMemoryMap() boot services function to convey memory resources to the OS loader. These resources must then be conveyed by the OS loader to OSPM.
The GetMemoryMap interface is only available at boot services time. It is not available as a run-time service after OSPM is loaded. The OS or its loader initiates the transition from boot services to run-time services by calling ExitBootServices() . After the call to ExitBootServices() all system memory map information must be derived from objects in the ACPI Namespace.
The GetMemoryMap() interface returns an array of UEFI memory descriptors. These memory descriptors define a system memory map of all the installed RAM, and of physical memory ranges reserved by the firmware. Each descriptor contains a type field that dictates how the physical address range is to be treated by the operating system. The table below defines the mapping from UEFI memory types (see UEFI Specification) to ACPI Address Range Types that:
Platform boot firmware shall follow if describing the memory range in both UEFI and legacy BIOS modes; and
aAn OS loader should use if it conveys that information to the OS using an ACPI E820h system address map table.
Type |
Mnemonic |
ACPI Address Range Type |
|---|---|---|
0 |
EfiReservedMemoryType |
AddressRangeReserved |
1 |
EfiLoaderCode |
AddressRangeMemory |
2 |
EfiLoaderData |
AddressRangeMemory |
3 |
EfiBootServicesCode |
AddressRangeMemory |
4 |
EfiBootServicesData |
AddressRangeMemory |
5 |
EfiRuntimeServiceCode |
AddressRangeReserved |
6 |
EfiRuntimeServicesDat a |
AddressRangeReserved |
7 |
EfiConventionalMemory |
AddressRangeMemory |
8 |
EfiUnusableMemory |
AddressRangeReserved |
9 |
EfiACPIReclaimMemory |
AddressRangeACPI |
10 |
EfiACPIMemoryNVS |
AddressRangeNVS |
11 |
EfiMemoryMappedIO |
AddressRangeReserved |
12 |
EfiMemoryMappedIOPort Space |
AddressRangeReserved |
13 |
EfiPalCode |
AddressRangeReserved |
14 |
EfiPersistentMemory |
AddressRangePersistentMemory |
15 to 0x6FFFFFFF |
Reserved. |
AddressRangeReserved |
0x70000000 to 0x7FFFFFFF |
Reserved for OEM used |
An OS should not use a memory type in the vendor-defined range because collisions may occur between different vendors. |
0x80000000 to 0xFFFFFFFF |
Reserved for use by UEFI OS loaders that are provided by operating system vendors |
OSV defined |
The table above applies to system firmware that supports legacy BIOS mode plus UEFI mode, and OS loaders.