From: George Guo KHO_TREE_MAX_DEPTH is calculated as: DIV_ROUND_UP(KHO_ORDER_0_LOG2 - KHO_BITMAP_SIZE_LOG2, KHO_TABLE_SIZE_LOG2) + 1 For systems with 16KB pages (e.g. LoongArch), this gives a depth of 4, with the top-level shift at bit 39. The order-0 bit sits at bit 50 (KHO_ORDER_0_LOG2 = 64 - PAGE_SHIFT = 50). When inserting or reading a key, the index extracted at the top level is: (1 << 50) >> 39 = 2048 2048 is exactly the table size (PAGE_SIZE / sizeof(phys_addr_t) = 2048 for 16KB pages), so it wraps to 0, aliasing the order bit to index 0 and losing it silently. On the second kernel, kho_radix_decode_key() sees a key without the order bit, calls fls64() on the wrong bit, computes a wrong order and thus a garbage physical address. phys_to_page() of that address faults in kho_preserved_memory_reserve(), causing a kernel panic early in boot. Fix by adding +1 to the DIV_ROUND_UP numerator so the formula accounts for the order bit itself, giving depth 5 for 16KB pages. The top-level shift becomes 50, and (1 << 50) >> 50 = 1, which is nonzero and unambiguous. For 4KB and 64KB page sizes the depth is unchanged. Fixes: 3f2ad90060f6 ("kho: adopt radix tree for preserved memory tracking") Tested-by: Kexin Liu Signed-off-by: George Guo --- include/linux/kho/abi/kexec_handover.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kho/abi/kexec_handover.h b/include/linux/kho/abi/kexec_handover.h index 7e847a2339b0..db9bda6dd310 100644 --- a/include/linux/kho/abi/kexec_handover.h +++ b/include/linux/kho/abi/kexec_handover.h @@ -274,7 +274,7 @@ enum kho_radix_consts { * and 1 bitmap level. */ KHO_TREE_MAX_DEPTH = - DIV_ROUND_UP(KHO_ORDER_0_LOG2 - KHO_BITMAP_SIZE_LOG2, + DIV_ROUND_UP(KHO_ORDER_0_LOG2 - KHO_BITMAP_SIZE_LOG2 + 1, KHO_TABLE_SIZE_LOG2) + 1, }; -- 2.25.1