On a KHO boot, a reserve_mem region that can't be revived is allocated from KHO_NOPRSRV memory, which includes the bootmem the next kernel boots out of. With CONFIG_KEXEC_HANDOVER_DEBUG, preserving the region then fails: WARNING: kernel/liveupdate/kexec_handover.c:1245 at kho_preserve_pages+0x168/0x180 failed to prepare memblock FDT for KHO: -22 Without it, the next kernel puts its memmap on top of the region and the ramoops records in it are lost. There is no use case for adding regions across a live update, so fail instead of allocating, and drop the TODO. Add an is_kho_boot() stub so the memblock tests still build. Fixes: f99230780211 ("memblock: add KHO support for reserve_mem") Reviewed-by: Pasha Tatashin Signed-off-by: Jose A. Perez de Azpillaga --- Changes in v3: - add an is_kho_boot() stub to the memblock tests (Mike). - add Pasha's Reviewed-by. Changes in v2: - fail on a KHO boot instead of allocating outside bootmem, as agreed with Pratyush [1]. this drops v1's patch 1. - not an RFC anymore. - based on v7.4-rc1. v2: https://lore.kernel.org/all/20261104204235.9066-1-azpijr@gmail.com/ v1: https://lore.kernel.org/all/20261021211058.83483-3-azpijr@gmail.com/ [1] https://lore.kernel.org/all/2vxzfqxglrg6.fsf@kernel.org/ mm/memblock.c | 11 ++++++++++- tools/testing/memblock/internal.h | 5 +++++ 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/mm/memblock.c b/mm/memblock.c index a450092a80fb..e325e0542c9a 100644 --- a/mm/memblock.c +++ b/mm/memblock.c @@ -2827,7 +2827,16 @@ static int __init reserve_mem(char *p) if (reserve_mem_kho_revive(name, size, align)) return 1; - /* TODO: Allocation must be outside of KHO_NOPRSRV region */ + /* + * On a KHO boot memblock only allocates from KHO_NOPRSRV memory here, + * which includes the bootmem the next kernel boots out of. Only regions + * handed over by the previous kernel are supported. + */ + if (is_kho_boot()) { + pr_err("reserve_mem: can't allocate \"%s\" on a KHO boot\n", name); + return -EOPNOTSUPP; + } + start = memblock_phys_alloc(size, align); if (!start) { pr_err("reserve_mem: memblock allocation failed\n"); diff --git a/tools/testing/memblock/internal.h b/tools/testing/memblock/internal.h index ba4d1c02fde5..84f22a964510 100644 --- a/tools/testing/memblock/internal.h +++ b/tools/testing/memblock/internal.h @@ -51,4 +51,9 @@ static inline bool kho_bootmem_overlap(phys_addr_t phys, size_t size) return false; } +static inline bool is_kho_boot(void) +{ + return false; +} + #endif base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4 -- 2.56.0