On Mon, Dec 08, 2025 at 06:53:15PM -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.
>
> Signed-off-by: Jason Miu <[email protected]>
> ---
> Documentation/core-api/kho/concepts.rst | 2 +-
> Documentation/core-api/kho/fdt.rst | 7 +
> Documentation/core-api/kho/index.rst | 1 +
> Documentation/core-api/kho/radix_tree.rst | 17 +
> include/linux/kho/abi/kexec_handover.h | 124 +++-
> include/linux/kho_radix_tree.h | 81 +++
> kernel/liveupdate/kexec_handover.c | 658 ++++++++++++----------
> 7 files changed, 568 insertions(+), 322 deletions(-)
> create mode 100644 Documentation/core-api/kho/radix_tree.rst
> create mode 100644 include/linux/kho_radix_tree.h
>
> diff --git a/Documentation/core-api/kho/concepts.rst
> b/Documentation/core-api/kho/concepts.rst
> index e96893937286..d38bcaa951e4 100644
> --- a/Documentation/core-api/kho/concepts.rst
> +++ b/Documentation/core-api/kho/concepts.rst
> @@ -71,7 +71,7 @@ in the FDT. That state is called the KHO finalization phase.
> Public API
> ==========
> .. kernel-doc:: kernel/liveupdate/kexec_handover.c
> - :export:
> + :identifiers: kho_is_enabled kho_restore_folio kho_restore_pages
> kho_add_subtree kho_remove_subtree kho_preserve_folio kho_unpreserve_folio
> kho_preserve_pages kho_unpreserve_pages kho_preserve_vmalloc
> kho_unpreserve_vmalloc kho_restore_vmalloc kho_alloc_preserve
> kho_unpreserve_free kho_restore_free is_kho_boot kho_retrieve_subtree
Ouch. This would be unmaintainable :(
>
> Internal API
> ============
...
> diff --git a/include/linux/kho/abi/kexec_handover.h
> b/include/linux/kho/abi/kexec_handover.h
> index 74f4fa67e458..bdda2fe67353 100644
> --- a/include/linux/kho/abi/kexec_handover.h
> +++ b/include/linux/kho/abi/kexec_handover.h
> @@ -10,6 +10,8 @@
> #ifndef _LINUX_KHO_ABI_KEXEC_HANDOVER_H
> #define _LINUX_KHO_ABI_KEXEC_HANDOVER_H
>
> +#include <linux/bits.h>
> +#include <linux/log2.h>
> #include <linux/types.h>
>
> /**
> @@ -35,25 +37,25 @@
> * parses this FDT to locate and restore the preserved data.::
> *
> * / {
> - * compatible = "kho-v1";
> + * compatible = "kho-v2";
> *
> * preserved-memory-map = <0x...>;
> *
> * <subnode-name-1> {
> - * fdt = <0x...>;
> + * preserved-data = <0x...>;
Please extend the paragraph describing "compatible" change in the commit
message to mention that "preserved-data" is a better name than "fdt"
because some subsystems will not use fdt format for their preserved state.
> * };
> *
> * <subnode-name-2> {
> - * fdt = <0x...>;
> + * preserved-data = <0x...>;
> * };
> * ... ...
> * <subnode-name-N> {
> - * fdt = <0x...>;
> + * preserved-data = <0x...>;
> * };
> * };
> *
> * Root KHO Node (/):
> - * - compatible: "kho-v1"
> + * - compatible: "kho-v2"
> *
> * Indentifies the overall KHO ABI version.
> *
> @@ -68,20 +70,20 @@
> * is provided by the subsystem that uses KHO for preserving its
> * data.
> *
> - * - fdt: u64
> + * - preserved-data: u64
> *
> - * Physical address pointing to a subnode FDT blob that is also
> + * Physical address pointing to a subnode data blob that is also
> * being preserved.
> */
>
> /* The compatible string for the KHO FDT root node. */
> -#define KHO_FDT_COMPATIBLE "kho-v1"
> +#define KHO_FDT_COMPATIBLE "kho-v2"
>
> /* The FDT property for the preserved memory map. */
> #define KHO_FDT_MEMORY_MAP_PROP_NAME "preserved-memory-map"
>
> /* The FDT property for sub-FDTs. */
> -#define KHO_FDT_SUB_TREE_PROP_NAME "fdt"
> +#define KHO_FDT_SUB_TREE_PROP_NAME "preserved-data"
>
> /**
> * DOC: Kexec Handover ABI for vmalloc Preservation
> @@ -159,4 +161,108 @@ struct kho_vmalloc {
> unsigned short order;
> };
>
> +/**
> + * DOC: Keep track of memory that is to be preserved across KHO.
Maybe "KHO persistent memory tracker"?
> + *
> + * KHO tracks preserved memory using a radix tree data structure. Each node
> of
> + * the tree is PAGE_SIZE. The leaf nodes are bitmaps where each set bit
Maybe "Each node of the tree is exactly a single page"?
> + * represents a single preserved page. The intermediate nodes are tables of
And here "a single preserved page" reads to me like a single order-0 page.
I think we should note that each bit can represent pages of different
orders.
> + * physical addresses that point to a lower level node.
> + *
> + * The tree hierarchy is shown below::
> + *
> + * root
> + * +-------------------+
> + * | Level 5 | (struct kho_radix_node)
> + * +-------------------+
> + * |
> + * v
> + * +-------------------+
> + * | Level 4 | (struct kho_radix_node)
> + * +-------------------+
> + * |
> + * | ... (intermediate levels)
> + * |
> + * v
> + * +-------------------+
> + * | Level 0 | (struct kho_radix_leaf)
> + * +-------------------+
> + *
> + * This is achieved by encoding the page's physical address (pa) and its
> order
It's not really clear what "this is achieved" refers to.
> + * into a single unsigned long value. This value is a key then used to
> traverse
This value is then used as a key to ...
> + * the tree. The encoded key value is composed of two parts: the 'order bit'
> in
> + * the upper part and the 'page offset' in the lower part.::
> + *
> + * +------------+-----------------------------+--------------------------+
> + * | Page Order | Order Bit | Page Offset |
> + * +------------+-----------------------------+--------------------------+
> + * | 0 | ...000100 ... (at bit 52) | pa >> (PAGE_SHIFT + 0) |
> + * | 1 | ...000010 ... (at bit 51) | pa >> (PAGE_SHIFT + 1) |
> + * | 2 | ...000001 ... (at bit 50) | pa >> (PAGE_SHIFT + 2) |
> + * | ... | ... | ... |
> + * +------------+-----------------------------+--------------------------+
> + *
> + * Page Offset:
> + * The 'page offset' is the physical address normalized for its order. It
> + * effectively represents the page offset for the given order.
> + *
> + * Order Bit:
> + * The 'order bit' encodes the page order by setting a single bit at a
> + * specific position. The position of this bit itself represents the order.
> + *
> + * For instance, on a 64-bit system with 4KB pages (PAGE_SHIFT = 12), the
> + * maximum range for a page offset (for order 0) is 52 bits (64 - 12). This
> + * offset occupies bits [0-51]. For order 0, the order bit is set at
> + * position 52.
> + *
> + * The following diagram illustrates how the encoded key value is split into
> + * indices for the tree levels, with PAGE_SIZE of 4KB::
> + *
> + * 63:60 59:51 50:42 41:33 32:24 23:15 14:0
> + *
> +---------+--------+--------+--------+--------+--------+-----------------+
> + * | 0 | Lv 5 | Lv 4 | Lv 3 | Lv 2 | Lv 1 | Lv 0 (bitmap)
> |
> + *
> +---------+--------+--------+--------+--------+--------+-----------------+
> + *
> + * This design stores pages of all sizes (orders) in a single 6-level table.
s/This design/The radix tree/ and s/table/hierarchy/
> + * It efficiently shares lower table levels, especially due to common zero
> top
> + * address bits, allowing a single, efficient algorithm to manage all pages.
> + * This bitmap approach also offers memory efficiency; for example, a 512KB
> + * bitmap can cover a 16GB memory range for 0-order pages with PAGE_SIZE =
> 4KB.
> + *
> + * The data structures defined here are part of the KHO ABI. Any modification
> + * to these structures that breaks backward compatibility must be
> accompanied by
> + * an update to the "compatible" string. This ensures that a newer kernel can
> + * correctly interpret the data passed by an older kernel.
> + */
> +
> +/*
> + * Defines constants for the KHO radix tree structure, used to track
> preserved
> + * memory. These constants govern the indexing, sizing, and depth of the
> tree.
> + */
> +enum kho_radix_consts {
> + /* The bit position of a 0-order page */
^ this is either position of the order bits or length of
the "page offset" for an order-0 page
> + KHO_ORDER_0_LG2 = 64 - PAGE_SHIFT,
I'd spell out LOG2 rather than LG2 here and below.
> +
> + /* Size of the table in kho_mem_radix_tree, in lg2 */
We don't have kho_mem_radix_tree anymore, do we?
> + KHO_TABLE_SIZE_LG2 = const_ilog2(PAGE_SIZE / sizeof(phys_addr_t)),
> +
> + /* Number of bits in the kho_bitmap, in lg2 */
> + KHO_BITMAP_SIZE_LG2 = PAGE_SHIFT + const_ilog2(BITS_PER_BYTE),
> +
> + /*
> + * The total tree depth is the number of intermediate levels
> + * and 1 bitmap level.
> + */
> + KHO_TREE_MAX_DEPTH = DIV_ROUND_UP(KHO_ORDER_0_LG2 - KHO_BITMAP_SIZE_LG2,
> + KHO_TABLE_SIZE_LG2) + 1,
> +};
> +
> +struct kho_radix_node {
> + u64 table[1 << KHO_TABLE_SIZE_LG2];
> +};
> +
> +struct kho_radix_leaf {
> + DECLARE_BITMAP(bitmap, 1 << KHO_BITMAP_SIZE_LG2);
> +};
> +
> #endif /* _LINUX_KHO_ABI_KEXEC_HANDOVER_H */
> diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
> new file mode 100644
> index 000000000000..5101a04f6ae6
> --- /dev/null
> +++ b/include/linux/kho_radix_tree.h
> @@ -0,0 +1,81 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _LIVEUPDATE_KEXEC_HANDOVER_RADIX_TREE_H
> +#define _LIVEUPDATE_KEXEC_HANDOVER_RADIX_TREE_H
Please use _LINUX_KHO_ABI prefix
> +
> +#include <linux/err.h>
> +#include <linux/errno.h>
> +#include <linux/types.h>
> +
> +/**
> + * DOC: Kexec Handover Radix Tree
> + *
> + * This is a radix tree implementation for tracking physical memory pages
> + * across kexec transitions. It was developed for the KHO mechanism but is
> + * designed for broader use by any subsystem that needs to preserve pages.
> + *
> + * The radix tree is a multi-level tree where leaf nodes are bitmaps
> + * representing individual pages. To allow pages of different sizes (orders)
> + * to be stored efficiently in a single tree, it uses a unique key encoding
> + * scheme. Each key is an unsigned long that combines a page's physical
> + * address and its order.
> + *
> + * Client code is responsible for allocating the root node of the tree and
> + * managing its lifecycle, and must use the tree data structures defined in
> + * the KHO ABI, `include/linux/kho/abi/kexec_handover.h`.
> + */
> +
> +struct kho_radix_node;
> +
> +typedef int (*kho_radix_tree_walk_callback_t)(unsigned long radix_key);
I don't think radix tree users outside kexec_handover.c should bother with
the key encoding.
The callback here should have physical address and order as parameters.
> +
> +#ifdef CONFIG_KEXEC_HANDOVER
> +
> +unsigned long kho_radix_encode_key(phys_addr_t pa, unsigned int order);
> +
> +phys_addr_t kho_radix_decode_key(unsigned long radix_key,
> + unsigned int *order);
These should not be a part of public interface.
> +int kho_radix_add_page(struct kho_radix_node *root, unsigned long pfn,
> + unsigned int order);
> +
> +void kho_radix_del_page(struct kho_radix_node *root, unsigned long pfn,
> + unsigned int order);
> +
> +int kho_radix_walk_tree(struct kho_radix_node *root, unsigned int level,
> + unsigned long start, kho_radix_tree_walk_callback_t cb);
> +
...
> diff --git a/kernel/liveupdate/kexec_handover.c
> b/kernel/liveupdate/kexec_handover.c
> index a180b3367e8f..81bac82c8672 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -66,155 +68,302 @@ static int __init kho_parse_enable(char *p)
> early_param("kho", kho_parse_enable);
...
> struct kho_mem_track {
> - /* Points to kho_mem_phys, each order gets its own bitmap tree */
> - struct xarray orders;
> + struct kho_radix_node *root;
> + struct rw_semaphore sem;
It does not look like we have concurrent readers, why choose rw_semaphore
and not mutex?
> };
>
> -struct khoser_mem_chunk;
> -
> struct kho_out {
> - void *fdt;
> - bool finalized;
The next patch removes finalization, probably removing the finalized field
should be done there.
> - struct mutex lock; /* protects KHO FDT finalization */
> -
> struct kho_mem_track track;
> + void *fdt;
> + struct mutex lock; /* protects KHO FDT */
Please don't move the fields around.
And while the update of the comment is correct, it seems to me rather a
part of the next patch.
> struct kho_debugfs dbg;
> };
>
> static struct kho_out kho_out = {
> - .lock = __MUTEX_INITIALIZER(kho_out.lock),
> .track = {
> - .orders = XARRAY_INIT(kho_out.track.orders, 0),
> + .sem = __RWSEM_INITIALIZER(kho_out.track.sem),
> },
> - .finalized = false,
> + .lock = __MUTEX_INITIALIZER(kho_out.lock),
Please don't to move fields.
> };
>
> -static void *xa_load_or_alloc(struct xarray *xa, unsigned long index)
> +/**
> + * kho_radix_encode_key - Encodes a physical address and order into a radix
> key.
> + * @pa: The physical address of the page.
> + * @order: The order of the page.
> + *
> + * This function combines a page's physical address and its order into a
> + * single unsigned long, which is used as a key for all radix tree
> + * operations.
> + *
> + * Return: The encoded unsigned long key.
> + */
> +unsigned long kho_radix_encode_key(phys_addr_t pa, unsigned int order)
> {
> - void *res = xa_load(xa, index);
> + /* Order bits part */
> + unsigned long h = 1UL << (KHO_ORDER_0_LG2 - order);
> + /* Page offset part */
> + unsigned long l = pa >> (PAGE_SHIFT + order);
>
> - if (res)
> - return res;
> + return h | l;
> +}
> +EXPORT_SYMBOL_GPL(kho_radix_encode_key);
>
> - void *elm __free(free_page) = (void *)get_zeroed_page(GFP_KERNEL);
> +/**
> + * kho_radix_decode_key - Decodes a radix key back into a physical address
> and order.
> + * @radix_key: The unsigned long key to decode.
> + * @order: An output parameter, a pointer to an unsigned int where the
> decoded
> + * page order will be stored.
> + *
> + * This function reverses the encoding performed by kho_radix_encode_key(),
> + * extracting the original physical address and page order from a given key.
> + *
> + * Return: The decoded physical address.
> + */
> +phys_addr_t kho_radix_decode_key(unsigned long radix_key,
> + unsigned int *order)
> +{
> + unsigned int order_bit = fls64(radix_key);
> + phys_addr_t pa;
>
> - if (!elm)
> - return ERR_PTR(-ENOMEM);
> + /* order_bit is numbered starting at 1 from fls64 */
> + *order = KHO_ORDER_0_LG2 - order_bit + 1;
> + /* The order is discarded by the shift */
> + pa = radix_key << (PAGE_SHIFT + *order);
>
> - if (WARN_ON(kho_scratch_overlap(virt_to_phys(elm), PAGE_SIZE)))
> - return ERR_PTR(-EINVAL);
> + return pa;
> +}
> +EXPORT_SYMBOL_GPL(kho_radix_decode_key);
Please make kho_radix_encode_key() and kho_radix_decode_key() static.
> +
> +static unsigned long kho_radix_get_index(unsigned long radix_key,
> + unsigned int level)
> +{
> + int s;
>
> - res = xa_cmpxchg(xa, index, NULL, elm, GFP_KERNEL);
> - if (xa_is_err(res))
> - return ERR_PTR(xa_err(res));
> - else if (res)
> - return res;
> + if (level == 0)
> + return radix_key % (1 << KHO_BITMAP_SIZE_LG2);
I'd split this to
static unsigned long kho_get_radix_bitmap_index(unsigned long key);
>
> - return no_free_ptr(elm);
> + s = ((level - 1) * KHO_TABLE_SIZE_LG2) + KHO_BITMAP_SIZE_LG2;
> + return (radix_key >> s) % (1 << KHO_TABLE_SIZE_LG2);
> }
>
> -static void __kho_unpreserve_order(struct kho_mem_track *track, unsigned
> long pfn,
> - unsigned int order)
> +/**
> + * kho_radix_add_page - Marks a page as preserved in the radix tree.
> + * @root: The root of the radix tree.
> + * @pfn: The page frame number of the page to preserve.
> + * @order: The order of the page.
> + *
> + * This function traverses the radix tree based on the key derived from @pfn
> + * and @order. It sets the corresponding bit in the leaf bitmap to mark the
> + * page for preservation. If intermediate nodes do not exist along the path,
> + * they are allocated and added to the tree.
> + *
> + * Return: 0 on success, or a negative error code on failure.
> + */
> +int kho_radix_add_page(struct kho_radix_node *root,
> + unsigned long pfn, unsigned int order)
> {
> - struct kho_mem_phys_bits *bits;
> - struct kho_mem_phys *physxa;
> - const unsigned long pfn_high = pfn >> order;
> + phys_addr_t pa = PFN_PHYS(pfn);
> + unsigned long radix_key = kho_radix_encode_key(pa, order);
pa seems unused elsewhere, you can just put PFN_PHYS() into
kho_radix_encode_key().
And radix_ prefix for the key seems redundant to me.
> + struct kho_radix_node *node;
> + struct kho_radix_leaf *leaf;
> + unsigned int i, idx;
> + int err = 0;
>
> - physxa = xa_load(&track->orders, order);
> - if (WARN_ON_ONCE(!physxa))
> - return;
> + /*
> + * This array stores pointers to newly allocated intermediate radix tree
> + * nodes along the insertion path. In case of an error during node
> + * allocation or insertion, these stored pointers are used to free
> + * the partially allocated path, preventing memory leaks.
> + */
> + struct kho_radix_node *intermediate_nodes[KHO_TREE_MAX_DEPTH] = { 0 };
Let's try keeping declarations in reverse xmas tree order. This long line
can be the first declaration.
And I don't think this array deserves such a long comment, it's quite
obvious why it's needed.
>
> - bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
> - if (WARN_ON_ONCE(!bits))
> - return;
> + might_sleep();
>
> - clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
> + node = root;
> +
> + /* Go from high levels to low levels */
> + for (i = KHO_TREE_MAX_DEPTH - 1; i > 0; i--) {
> + idx = kho_radix_get_index(radix_key, i);
> +
> + if (node->table[idx]) {
> + node = phys_to_virt((phys_addr_t)node->table[idx]);
Is casting to phys_addr_t required?
We should have an assert that verifies that phys_addr_t and u64 have the
same size somewhere, otherwise everything falls apart anyway.
> + continue;
> + }
> +
> + /* Next node is empty, create a new node for it */
> + struct kho_radix_node *new_tree;
Please don't mix declarations and code unless strictly necessary.
And new_node seems a more appropriate name here.
> +
> + new_tree = (struct kho_radix_node *)get_zeroed_page(GFP_KERNEL);
> + if (!new_tree) {
> + err = -ENOMEM;
> + goto err_free_alloc_nodes;
This reads to me like "on error free and allocate nodes". err_free_nodes
sounds a better name.
> + }
> +
> + node->table[idx] = virt_to_phys(new_tree);
> + node = new_tree;
> +
> + intermediate_nodes[i] = new_tree;
> + }
> +
> + /* Handle the leaf level bitmap (level 0) */
> + idx = kho_radix_get_index(radix_key, 0);
> + leaf = (struct kho_radix_leaf *)node;
> + __set_bit(idx, leaf->bitmap);
> +
> + return 0;
> +
> +err_free_alloc_nodes:
> + for (i = KHO_TREE_MAX_DEPTH - 1; i > 0; i--) {
> + if (intermediate_nodes[i])
> + free_page((unsigned long)intermediate_nodes[i]);
> + }
> +
> + return err;
> }
> +EXPORT_SYMBOL_GPL(kho_radix_add_page);
>
> -static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
> - unsigned long end_pfn)
> +/**
> + * kho_radix_del_page - Removes a page's preservation status from the radix
> tree.
> + * @root: The root of the radix tree.
> + * @pfn: The page frame number of the page to unpreserve.
> + * @order: The order of the page.
> + *
> + * This function traverses the radix tree and clears the bit corresponding to
> + * the page, effectively removing its "preserved" status. It does not free
> + * the tree's intermediate nodes, even if they become empty.
> + */
> +void kho_radix_del_page(struct kho_radix_node *root, unsigned long pfn,
> + unsigned int order)
> {
> - unsigned int order;
> + unsigned long radix_key = kho_radix_encode_key(PFN_PHYS(pfn), order);
> + unsigned int tree_level = KHO_TREE_MAX_DEPTH - 1;
> + struct kho_radix_node *node;
> + struct kho_radix_leaf *leaf;
> + unsigned int i, idx;
>
> - while (pfn < end_pfn) {
> - order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
> + might_sleep();
>
> - __kho_unpreserve_order(track, pfn, order);
> + node = root;
This can be done at declaration spot.
>
> - pfn += 1 << order;
> + /* Go from high levels to low levels */
> + for (i = tree_level; i > 0; i--) {
tree_level seems unnecessary, just use KHO_TREE_MAX_DEPTH - 1.
> + idx = kho_radix_get_index(radix_key, i);
> +
> + /*
> + * Attempting to delete a page that has not been preserved,
> + * return with a warning.
> + */
> + if (WARN_ON(!node->table[idx]))
> + return;
> +
> + if (node->table[idx])
> + node = phys_to_virt((phys_addr_t)node->table[idx]);
> }
> +
> + /* Handle the leaf level bitmap (level 0) */
> + leaf = (struct kho_radix_leaf *)node;
idx should be updated here for level 0.
> + __clear_bit(idx, leaf->bitmap);
> }
> +EXPORT_SYMBOL_GPL(kho_radix_del_page);
...
> +
> +/**
> + * kho_radix_walk_tree - Traverses the radix tree and calls a callback for
> each preserved page.
> + * @root: A pointer to the root node of the radix tree to walk.
> + * @level: The starting level for the walk (typically KHO_TREE_MAX_DEPTH -
> 1).
> + * @start: The initial key prefix for the walk (typically 0).
> + * @cb: A callback function of type kho_radix_tree_walk_callback_t that will
> be
> + * invoked for each preserved page found in the tree. The callback
> receives
> + * the full radix key of the preserved page.
> + *
> + * This function walks the radix tree, searching from the specified top level
> + * (@level) down to the lowest level (level 0). For each preserved page
> found,
> + * it invokes the provided callback, passing the page's fully reconstructed
> + * radix key.
> + *
> + * Return: 0 if the walk completed the specified subtree, or the non-zero
> return
> + * value from the callback that stopped the walk.
> + */
> +int kho_radix_walk_tree(struct kho_radix_node *root, unsigned int level,
> + unsigned long start, kho_radix_tree_walk_callback_t cb)
> +{
> + struct kho_radix_node *node;
> + struct kho_radix_leaf *leaf;
> + unsigned long radix_key, i;
> + int err;
>
> - new_physxa = kzalloc(sizeof(*physxa), GFP_KERNEL);
> - if (!new_physxa)
> - return -ENOMEM;
> + for (i = 0; i < PAGE_SIZE / sizeof(phys_addr_t); i++) {
> + if (!root->table[i])
> + continue;
> +
> + unsigned int shift;
Please don't mix declarations and code unless strictly necessary.
>
> - xa_init(&new_physxa->phys_bits);
> - physxa = xa_cmpxchg(&track->orders, order, NULL, new_physxa,
> - GFP_KERNEL);
> + shift = ((level - 1) * KHO_TABLE_SIZE_LG2) +
> + KHO_BITMAP_SIZE_LG2;
> + radix_key = start | (i << shift);
>
> - err = xa_err(physxa);
> - if (err || physxa) {
> - xa_destroy(&new_physxa->phys_bits);
> - kfree(new_physxa);
> + node = phys_to_virt((phys_addr_t)root->table[i]);
>
> + if (level > 1) {
> + err = kho_radix_walk_tree(node, level - 1,
> + radix_key, cb);
> if (err)
> return err;
> } else {
> - physxa = new_physxa;
> + /*
> + * we are at level 1,
> + * node is pointing to the level 0 bitmap.
> + */
> + leaf = (struct kho_radix_leaf *)node;
> + return kho_radix_walk_leaf(leaf, radix_key, cb);
I'd inverse the if:
if (!level)
return kho_radix_walk_leaf();
err = kho_radix_walk_tree()
> }
> }
>
> - bits = xa_load_or_alloc(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
> - if (IS_ERR(bits))
> - return PTR_ERR(bits);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(kho_radix_walk_tree);
> +
Feels like an extra empty line is added here. Please drop it.
>
> - set_bit(pfn_high % PRESERVE_BITS, bits->preserve);
>
> - return 0;
> +static void __kho_unpreserve(unsigned long pfn, unsigned long end_pfn)
The change of __kho_unpreserve() signature does not belong to this patch.
If you feel strongly this change is justified make it a preparation patch
before the radix tree changes.
> +{
> + struct kho_mem_track *track = &kho_out.track;
> + unsigned int order;
> +
> + if (WARN_ON_ONCE(!track->root))
> + return;
> +
> + down_write(&track->sem);
> + while (pfn < end_pfn) {
> + order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
> +
> + kho_radix_del_page(track->root, pfn, order);
If we are going to expose radix tree APIs, it would make sense for them to
take care of the locking internally.
For that we might need something like
struct kho_radix_tree {
struct kho_radix_node *root;
struct mutex lock;
};
and use the root struct as the parameter to kho_radix APIs.
> +
> + pfn += 1 << order;
> + }
> + up_write(&track->sem);
> }
...
> -static void kho_update_memory_map(struct khoser_mem_chunk *first_chunk)
> +static int __init kho_radix_walk_tree_memblock_callback(unsigned long
> radix_key)
This name is much about being a callback for walking the tree and very
little about what the function does. It should be the other way around.
> {
> + union kho_page_info info;
> + unsigned int order;
> + unsigned long pa;
In the most places we use 'phys_addr_t phys' for physical addresses.
> + struct page *page;
> + int sz;
>
> + pa = kho_radix_decode_key(radix_key, &order);
>
> + sz = 1 << (order + PAGE_SHIFT);
> + page = phys_to_page(pa);
>
> + /* Reserve the memory preserved in KHO radix tree in memblock */
> + memblock_reserve(pa, sz);
> + memblock_reserved_mark_noinit(pa, sz);
> + info.magic = KHO_PAGE_MAGIC;
> + info.order = order;
> + page->private = info.page_private;
>
> return 0;
> }
>
>
>
Too many empty lines here.
> /*
> * With KHO enabled, memory can become fragmented because KHO regions may
> @@ -789,14 +774,22 @@ EXPORT_SYMBOL_GPL(kho_remove_subtree);
> */
> int kho_preserve_folio(struct folio *folio)
> {
> + struct kho_mem_track *track = &kho_out.track;
> const unsigned long pfn = folio_pfn(folio);
> const unsigned int order = folio_order(folio);
> - struct kho_mem_track *track = &kho_out.track;
> + int err;
>
> if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
> return -EINVAL;
>
> - return __kho_preserve_order(track, pfn, order);
> + if (WARN_ON_ONCE(!track->root))
> + return -EINVAL;
Can we move this to kho_radix_add_page() and kho_radix_del_page()?
I see that some preserve/unpreserve methods WARN and some don't.
> +
> + down_write(&track->sem);
> + err = kho_radix_add_page(track->root, pfn, order);
> + up_write(&track->sem);
> +
> + return err;
> }
> EXPORT_SYMBOL_GPL(kho_preserve_folio);
...
> @@ -1213,25 +1214,12 @@ EXPORT_SYMBOL_GPL(kho_restore_free);
>
> int kho_finalize(void)
> {
> - int ret;
> -
> - if (!kho_enable)
> - return -EOPNOTSUPP;
> -
> - guard(mutex)(&kho_out.lock);
> - ret = kho_mem_serialize(&kho_out);
> - if (ret)
> - return ret;
> -
> - kho_out.finalized = true;
> -
> return 0;
> }
>
> bool kho_finalized(void)
> {
> - guard(mutex)(&kho_out.lock);
> - return kho_out.finalized;
> + return false;
Most of the finalization changes belong to the next patch IMO.
> }
>
> struct kho_in {
> @@ -1304,18 +1292,49 @@ int kho_retrieve_subtree(const char *name,
> phys_addr_t *phys)
> }
> EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
>
> +/* Return non-zero if error */
That's what 99% of the kernel does, no need to comment about it.
> static __init int kho_out_fdt_setup(void)
> {
> + struct kho_mem_track *track = &kho_out.track;
> void *root = kho_out.fdt;
> - u64 empty_mem_map = 0;
> + u64 preserved_mem_tree_pa;
> int err;
>
> err = fdt_create(root, PAGE_SIZE);
> err |= fdt_finish_reservemap(root);
> err |= fdt_begin_node(root, "");
> err |= fdt_property_string(root, "compatible", KHO_FDT_COMPATIBLE);
> - err |= fdt_property(root, KHO_FDT_MEMORY_MAP_PROP_NAME, &empty_mem_map,
> - sizeof(empty_mem_map));
> +
> + down_read(&track->sem);
> + preserved_mem_tree_pa = (u64)virt_to_phys(track->root);
> + up_read(&track->sem);
It seems to be the only place that uses down_read(). So we actually don't
have concurrent readers. Let's just use a mutex.
> +
> + err |= fdt_property(root, KHO_FDT_MEMORY_MAP_PROP_NAME,
> + &preserved_mem_tree_pa,
> + sizeof(preserved_mem_tree_pa));
> +
> err |= fdt_end_node(root);
> err |= fdt_finish(root);
>
> @@ -1324,16 +1343,26 @@ static __init int kho_out_fdt_setup(void)
>
> static __init int kho_init(void)
> {
> + struct kho_mem_track *track = &kho_out.track;
> const void *fdt = kho_get_fdt();
> int err = 0;
>
> if (!kho_enable)
> return 0;
>
> + down_write(&track->sem);
> + track->root = (struct kho_radix_node *)
> + kzalloc(PAGE_SIZE, GFP_KERNEL);
> + up_write(&track->sem);
> + if (!track->root) {
> + err = -ENOMEM;
> + goto err_free_scratch;
> + }
> +
> kho_out.fdt = kho_alloc_preserve(PAGE_SIZE);
> if (IS_ERR(kho_out.fdt)) {
> err = PTR_ERR(kho_out.fdt);
> - goto err_free_scratch;
> + goto err_free_kho_radix_tree_root;
> }
>
> err = kho_debugfs_init();
> @@ -1379,6 +1408,11 @@ static __init int kho_init(void)
>
> err_free_fdt:
> kho_unpreserve_free(kho_out.fdt);
> +
> +err_free_kho_radix_tree_root:
> + kfree(track->root);
> + track->root = NULL;
> +
No need for empty lines around the error handling
> err_free_scratch:
> kho_out.fdt = NULL;
> for (int i = 0; i < kho_scratch_cnt; i++) {
> @@ -1422,7 +1456,7 @@ void __init kho_memory_init(void)
> kho_scratch = phys_to_virt(kho_in.scratch_phys);
> kho_release_scratch();
>
> - if (!kho_mem_deserialize(kho_get_fdt()))
> + if (kho_mem_retrieve(kho_get_fdt()))
> kho_in.fdt_phys = 0;
> } else {
> kho_reserve_scratch();
--
Sincerely yours,
Mike.
