When KHO (Kexec HandOver) is enabled, it sets up scratch memory regions early during device tree scanning. After kexec, the new kernel exclusively uses this region for memory allocations during boot up to the initialization of the page allocator
However, when booting with EFI, EFI's reserve_regions() uses memblock_remove(0, PHYS_ADDR_MAX) to clear all memory regions before rebuilding them from EFI data. This destroys KHO scratch regions and their flags, thus causing a kernel panic, as there are no scratch memory regions. Instead of wholesale removal, iterate through memory regions and only remove non-KHO ones. This preserves KHO scratch regions while still allowing EFI to rebuild its memory map. Signed-off-by: Evangelos Petrongonas <epet...@amazon.de> --- Reproduction/Verification Steps The issue and the fix can be reproduced/verified by booting a VM with EFI and attempting to perform a KHO enabled kexec. The fix was developed/tested on arm64. drivers/firmware/efi/efi-init.c | 31 +++++++++++++++++++++++++++---- 1 file changed, 27 insertions(+), 4 deletions(-) diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c index a00e07b853f22..2f08b1ab764f6 100644 --- a/drivers/firmware/efi/efi-init.c +++ b/drivers/firmware/efi/efi-init.c @@ -164,12 +164,35 @@ static __init void reserve_regions(void) pr_info("Processing EFI memory map:\n"); /* - * Discard memblocks discovered so far: if there are any at this - * point, they originate from memory nodes in the DT, and UEFI - * uses its own memory map instead. + * Discard memblocks discovered so far except for KHO scratch regions. + * Most memblocks at this point originate from memory nodes in the DT, + * and UEFI uses its own memory map instead. However, if KHO is enabled, + * scratch regions must be preserved. */ memblock_dump_all(); - memblock_remove(0, PHYS_ADDR_MAX); + + if (IS_ENABLED(CONFIG_MEMBLOCK_KHO_SCRATCH)) { + struct memblock_region *reg; + phys_addr_t start, size; + int i; + + /* Remove all non-KHO regions */ + for (i = memblock.memory.cnt - 1; i >= 0; i--) { + reg = &memblock.memory.regions[i]; + if (!memblock_is_kho_scratch(reg)) { + start = reg->base; + size = reg->size; + memblock_remove(start, size); + } + } + } else { + /* + * KHO is disabled. Discard memblocks discovered so far: if there + * are any at this point, they originate from memory nodes in the + * DT, and UEFI uses its own memory map instead. + */ + memblock_remove(0, PHYS_ADDR_MAX); + } for_each_efi_memory_desc(md) { paddr = md->phys_addr; -- 2.43.0 Amazon Web Services Development Center Germany GmbH Tamara-Danz-Str. 13 10243 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597