linux-kernel - [PATCH v3 0/2] efi: Fix EFI boot with kexec handover (KHO)

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Message-ID: <cover.1755721529.git.epetron@amazon.de>
Date: Thu, 21 Aug 2025 17:58:58 +0000
From: Evangelos Petrongonas <epetron@...zon.de>
To: Ard Biesheuvel <ardb@...nel.org>, Mike Rapoport <rppt@...nel.org>
CC: Evangelos Petrongonas <epetron@...zon.de>, Alexander Graf
	<graf@...zon.com>, Changyuan Lyu <changyuanl@...gle.com>, Andrew Morton
	<akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
	<kexec@...ts.infradead.org>, <linux-mm@...ck.org>,
	<linux-efi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nh-open-source@...zon.com>
Subject: [PATCH v3 0/2] efi: Fix EFI boot with kexec handover (KHO)

This patch series fixes a kernel panic that occurs when booting with
both EFI and KHO (Kexec HandOver) enabled.

The issue arises because EFI's `reserve_regions()` clears all memory
regions with `memblock_remove(0, PHYS_ADDR_MAX)` before rebuilding them
from EFI data. This destroys KHO scratch regions that were set up early
during device tree scanning, causing a panic as the kernel has no valid
memory regions for early allocations.

The first patch introduces `is_kho_boot()` to allow early boot
components to reliably detect if the kernel was booted via KHO-enabled
kexec. The existing `kho_is_enabled()` only checks the command line and
doesn't verify if an actual KHO FDT was passed.

The second patch modifies EFI's `reserve_regions()` to selectively
remove only non-KHO memory regions when KHO is active, preserving the
critical scratch regions while still allowing EFI to rebuild its memory
map.

The patchset was developed/tested on arm64.

Main Changes in v3 (smaller changes can be found in individual patches):
    - Condition is_kho_boot only on the existence of a KHO FDT
    - Add Reviewed-by/Acked-by

Main Changes in v2:
    - Introduce is_kho_boot()
    - Replace manual loop with for_each_mem_region macro

Evangelos Petrongonas (2):
  kexec: introduce is_kho_boot()
  efi: Support booting with kexec handover (KHO)

 drivers/firmware/efi/efi-init.c | 29 +++++++++++++++++++++++++----
 include/linux/kexec_handover.h  |  6 ++++++
 kernel/kexec_handover.c         | 20 ++++++++++++++++++++
 3 files changed, 51 insertions(+), 4 deletions(-)

-- 
2.47.3

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