The EFI stub in the ARM kernel runs in the context of the firmware, which means it usually runs with the caches and MMU on. Currently, we relocate the zImage so it appears in the first 128 MiB, disable the MMU and caches and invoke the decompressor via its ordinary entry point. However, since we can pass the base of DRAM directly, there is no need to relocate the zImage, which also means there is no need to disable and re-enable the caches and create new page tables etc. This simplification is implemented by patch #5. Patches #1 - #4 are prerequisite changes to permit the decompressor startup code to be invoked past its ordinary entry point, and execute from the offset where the UEFI firmware happened to load it. Note that this applies onto rmk/for-next as of today. Changes since v3: - rebase onto rmk/for-next with Geert's DT memory node patch [0] removed, as it has been reverted again due to regressions Changes since v2: - Set the LSB of the image address if we are entering with MMU and caches off, so that the decompressor will install its own page tables as it usually does. This might happen on U-Boot platforms that call 'bootefi' without enabling the caches (which technically violates the UEFI spec, but might be working fine today) - Add Nico's ack to the series Changes since v1: - Tweak some asm sequences in #2 to fix the Thumb2 build - Switch immediately to the new stack in #5 Cc: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> Cc: Nicolas Pitre <nico@xxxxxxxxxxx> Cc: Linus Walleij <linus.walleij@xxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxx> Cc: Heinrich Schuchardt <xypron.glpk@xxxxxx> [0] https://lore.kernel.org/linux-arm-kernel/20200429082120.16259-1-geert+renesas@xxxxxxxxx/ Ard Biesheuvel (5): ARM: decompressor: move headroom variable out of LC0 ARM: decompressor: split off _edata and stack base into separate object ARM: decompressor: defer loading of the contents of the LC0 structure ARM: decompressor: move GOT into .data for EFI enabled builds ARM: decompressor: run decompressor in place if loaded via UEFI arch/arm/boot/compressed/head.S | 79 ++++++++------------ arch/arm/boot/compressed/vmlinux.lds.S | 5 ++ drivers/firmware/efi/libstub/arm32-stub.c | 45 ++--------- 3 files changed, 43 insertions(+), 86 deletions(-) -- 2.17.1
