During early initialisation, after a kexec, other components, like EFI need to know if a KHO enabled kexec is performed. The `kho_is_enabled` function is not enough as in the early stages, it only reflects whether the cmdline has KHO enabled, not if an actual KHO FDT exists. Extend the KHO API with `is_kho_boot()` to provide a way for components to check if a KHO enabled kexec is performed. Signed-off-by: Evangelos Petrongonas --- include/linux/kexec_handover.h | 6 ++++++ kernel/kexec_handover.c | 20 ++++++++++++++++++++ 2 files changed, 26 insertions(+) diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h index 348844cffb13..559d13a3bc44 100644 --- a/include/linux/kexec_handover.h +++ b/include/linux/kexec_handover.h @@ -40,6 +40,7 @@ struct kho_serialization; #ifdef CONFIG_KEXEC_HANDOVER bool kho_is_enabled(void); +bool is_kho_boot(void); int kho_preserve_folio(struct folio *folio); int kho_preserve_phys(phys_addr_t phys, size_t size); @@ -60,6 +61,11 @@ static inline bool kho_is_enabled(void) return false; } +static inline bool is_kho_boot(void) +{ + return false; +} + static inline int kho_preserve_folio(struct folio *folio) { return -EOPNOTSUPP; diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c index 69b953551677..a1a4e76e0ff1 100644 --- a/kernel/kexec_handover.c +++ b/kernel/kexec_handover.c @@ -925,6 +925,26 @@ static const void *kho_get_fdt(void) return kho_in.fdt_phys ? phys_to_virt(kho_in.fdt_phys) : NULL; } +/** + * is_kho_boot - check if current kernel was booted via KHO-enabled + * kexec + * + * This function checks if the current kernel was loaded through a kexec + * operation with KHO enabled, by verifying both that KHO is enabled via + * cmdline AND that a valid KHO FDT was passed. + * + * Note: This function returns reliable results only after + * kho_populate() has been called during early boot. Before that, + * it may return false even if KHO data is present. + * + * Return: true if booted via KHO-enabled kexec, false otherwise + */ +bool is_kho_boot(void) +{ + return !!kho_get_fdt() && kho_enable; +} +EXPORT_SYMBOL_GPL(is_kho_boot); + /** * kho_retrieve_subtree - retrieve a preserved sub FDT by its name. * @name: the name of the sub FDT passed to kho_add_subtree(). -- 2.47.3 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 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, which are good known memory, while still allowing EFI to rebuild its memory map. Signed-off-by: Evangelos Petrongonas --- Changes in v2: - Replaced the for loop with for_each_mem_region - Fixed comment indentation - Amended commit message to specify that scratch regions are known good regions drivers/firmware/efi/efi-init.c | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) diff --git a/drivers/firmware/efi/efi-init.c b/drivers/firmware/efi/efi-init.c index a00e07b853f2..99f7eecc320f 100644 --- a/drivers/firmware/efi/efi-init.c +++ b/drivers/firmware/efi/efi-init.c @@ -12,6 +12,7 @@ #include #include #include +#include #include #include #include @@ -164,12 +165,31 @@ 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_kho_boot()) { + struct memblock_region *r; + + /* Remove all non-KHO regions */ + for_each_mem_region(r) { + if (!memblock_is_kho_scratch(r)) { + memblock_remove(r->base, r->size); + r--; + } + } + } 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; -- 2.47.3 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