1.. SPDX-License-Identifier: GPL-2.0 2 3===================================== 4General note on [U]EFI x86_64 support 5===================================== 6 7The nomenclature EFI and UEFI are used interchangeably in this document. 8 9Although the tools below are _not_ needed for building the kernel, 10the needed bootloader support and associated tools for x86_64 platforms 11with EFI firmware and specifications are listed below. 12 131. UEFI specification: http://www.uefi.org 14 152. Booting Linux kernel on UEFI x86_64 platform can either be 16 done using the <Documentation/admin-guide/efi-stub.rst> or using a 17 separate bootloader. 18 193. x86_64 platform with EFI/UEFI firmware. 20 21Mechanics 22--------- 23 24Refer to <Documentation/admin-guide/efi-stub.rst> to learn how to use the EFI stub. 25 26Below are general EFI setup guidelines on the x86_64 platform, 27regardless of whether you use the EFI stub or a separate bootloader. 28 29- Build the kernel with the following configuration:: 30 31 CONFIG_FB_EFI=y 32 CONFIG_FRAMEBUFFER_CONSOLE=y 33 34 If EFI runtime services are expected, the following configuration should 35 be selected:: 36 37 CONFIG_EFI=y 38 CONFIG_EFIVAR_FS=y or m # optional 39 40- Create a VFAT partition on the disk with the EFI System flag 41 You can do this with fdisk with the following commands: 42 43 1. g - initialize a GPT partition table 44 2. n - create a new partition 45 3. t - change the partition type to "EFI System" (number 1) 46 4. w - write and save the changes 47 48 Afterwards, initialize the VFAT filesystem by running mkfs:: 49 50 mkfs.fat /dev/<your-partition> 51 52- Copy the boot files to the VFAT partition: 53 If you use the EFI stub method, the kernel acts also as an EFI executable. 54 55 You can just copy the bzImage to the EFI/boot/bootx64.efi path on the partition 56 so that it will automatically get booted, see the <Documentation/admin-guide/efi-stub.rst> page 57 for additional instructions regarding passage of kernel parameters and initramfs. 58 59 If you use a custom bootloader, refer to the relevant documentation for help on this part. 60 61- If some or all EFI runtime services don't work, you can try following 62 kernel command line parameters to turn off some or all EFI runtime 63 services. 64 65 noefi 66 turn off all EFI runtime services 67 reboot_type=k 68 turn off EFI reboot runtime service 69 70- If the EFI memory map has additional entries not in the E820 map, 71 you can include those entries in the kernels memory map of available 72 physical RAM by using the following kernel command line parameter. 73 74 add_efi_memmap 75 include EFI memory map of available physical RAM 76