Hi Jason, On Thu, Jan 15, 2026 at 07:44:31PM -0800, Jason Miu wrote: > Introduce a radix tree implementation for tracking preserved memory > pages and switch the KHO memory tracking mechanism to use it. This > lays the groundwork for a stateless KHO implementation that eliminates > the need for serialization and the associated "finalize" state. > > This patch introduces the core radix tree data structures and > constants to the KHO ABI. It adds the radix tree node and leaf > structures, along with documentation for the radix tree key encoding > scheme that combines a page's physical address and order. > > To support broader use by other kernel subsystems, such as hugetlb > preservation, the core radix tree manipulation functions are exported > as a public API. > > The xarray-based memory tracking is replaced with this new radix tree > implementation. The core KHO preservation and unpreservation functions > are wired up to use the radix tree helpers. On boot, the second kernel > restores the preserved memory map by walking the radix tree whose root > physical address is passed via the FDT. > > The ABI `compatible` version is bumped to "kho-v2" to reflect the > structural changes in the preserved memory map and sub-FDT property > names. This includes renaming "fdt" to "preserved-data" to better > reflect that preserved state may use formats other than FDT. > > Signed-off-by: Jason Miu <[email protected]>
... > diff --git a/kernel/liveupdate/kexec_handover.c > b/kernel/liveupdate/kexec_handover.c > index 49bf2cecab12..06adaf56cd69 100644 > --- a/kernel/liveupdate/kexec_handover.c > +++ b/kernel/liveupdate/kexec_handover.c > @@ -5,6 +5,7 @@ > * Copyright (C) 2025 Microsoft Corporation, Mike Rapoport <[email protected]> > * Copyright (C) 2025 Google LLC, Changyuan Lyu <[email protected]> > * Copyright (C) 2025 Pasha Tatashin <[email protected]> > + * Copyright (C) 2025 Google LLC, Jason Miu <[email protected]> It's already 2026 ;-) > */ > > #define pr_fmt(fmt) "KHO: " fmt ... > +int kho_radix_add_page(struct kho_radix_tree *tree, > + unsigned long pfn, unsigned int order) > +{ > + /* Newly allocated nodes for error cleanup */ > + struct kho_radix_node *intermediate_nodes[KHO_TREE_MAX_DEPTH] = { 0 }; > + unsigned long key = kho_radix_encode_key(PFN_PHYS(pfn), order); > + struct kho_radix_node *new_node, *anchor_node; > + struct kho_radix_node *node = tree->root; > + unsigned int i, idx, anchor_idx; > + struct kho_radix_leaf *leaf; > + int err = 0; > + > + if (WARN_ON_ONCE(!tree->root)) > + return -EINVAL; > + > + might_sleep(); > + > + guard(mutex)(&tree->lock); > + > + /* Go from high levels to low levels */ > + for (i = KHO_TREE_MAX_DEPTH - 1; i > 0; i--) { > + idx = kho_radix_get_table_index(key, i); > + > + if (node->table[idx]) { > + node = phys_to_virt(node->table[idx]); > + continue; > + } > + > + /* Next node is empty, create a new node for it */ > + new_node = (struct kho_radix_node *)get_zeroed_page(GFP_KERNEL); > + if (!new_node) { > + err = -ENOMEM; > + goto err_free_nodes; > + } > + > + node->table[idx] = virt_to_phys(new_node); > + > + /* > + * Capture the node where the new branch starts for cleanup > + * if allocation fails. > + */ > + if (!anchor_node) { I think anchor_node should be initialized to NULL for this to work. > + anchor_node = node; > + anchor_idx = idx; > + } > + intermediate_nodes[i] = new_node; > + > + node = new_node; > + } > + > + /* Handle the leaf level bitmap (level 0) */ > + idx = kho_radix_get_bitmap_index(key); > + leaf = (struct kho_radix_leaf *)node; > + __set_bit(idx, leaf->bitmap); > + > + return 0; > + > +err_free_nodes: > + for (i = KHO_TREE_MAX_DEPTH - 1; i > 0; i--) { > + if (intermediate_nodes[i]) > + free_page((unsigned long)intermediate_nodes[i]); > + } > + if (anchor_node) > + anchor_node->table[anchor_idx] = 0; > + > + return err; > +} > +EXPORT_SYMBOL_GPL(kho_radix_add_page); ... > + if (WARN_ON(!node->table[idx])) > + return; > + > + node = phys_to_virt((phys_addr_t)node->table[idx]); No need for casting. > + shift = ((level - 1) * KHO_TABLE_SIZE_LOG2) + > + KHO_BITMAP_SIZE_LOG2; > + key = start | (i << shift); > + > + node = phys_to_virt((phys_addr_t)root->table[i]); Ditto. > @@ -1466,12 +1489,6 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 > fdt_len, > goto out; > } > > - mem_map_phys = kho_get_mem_map_phys(fdt); > - if (!mem_map_phys) { > - err = -ENOENT; > - goto out; > - } I think we should keep the logic that skips scratch initialization if there were no memory preservations, like Pasha implemented here: https://lkml.kernel.org/r/[email protected] (commit e1c3bfd091f3 ("kho: validate preserved memory map during population") in today's mm tree) We just should update the validation to work with the radix tree. > scratch = early_memremap(scratch_phys, scratch_len); > if (!scratch) { > pr_warn("setup: failed to memremap scratch (phys=0x%llx, > len=%lld)\n", > @@ -1512,7 +1529,6 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 > fdt_len, > > kho_in.fdt_phys = fdt_phys; > kho_in.scratch_phys = scratch_phys; > - kho_in.mem_map_phys = mem_map_phys; > kho_scratch_cnt = scratch_cnt; > pr_info("found kexec handover data.\n"); > > -- > 2.52.0.457.g6b5491de43-goog > -- Sincerely yours, Mike.
