[PATCH 00/12] kho: make boot time huge page allocation work nicely with KHO

[PATCH 00/12] kho: make boot time huge page allocation work nicely with KHO

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Hi,

Gigantic huge page allocation is somewhat broken currently with KHO.

First, they break scratch size accounting. Since they are allocated
using the memblock alloc APIs, they count towards RSRV_KERN, and this
scratch size when using scratch_scale. This means if huge pages take a
large enough chunk of system memory scratch size will blow up and fail
to allocate.

Second, scratch can not contain preserved memory, and if hugepages are
allocated from scratch, they will fail to be preserved with the upcoming
hugetlb preservation series [0].

Fix this by introducing the concept of extended scratch areas. They are
areas that the kernel discovers on boot by walking the radix tree and
finding free memory ranges. See patch 10 for more details.

Discovering the scratch areas needs some changes to the radix tree APIs
and to memblock. Patches 1-8 do that.

Patch 9 introduces extended scratch to memblock.

Patch 10 adds the extended scratch discovery logic.

Patch 11 cleans up the preserved memory map API.

Finally, patch 12 puts all the pieces together and uses only extended
scratch for hugepage allocation and does not count then towards
RSRV_KERN.

[0] https://lore.kernel.org/linux-mm/20251206230222.853493-1-pratyush@kernel.org/T/#u

Regards,
Pratyush Yadav

Pratyush Yadav (Google) (12):
  kho: generalize radix tree APIs
  kho: store incoming radix tree in kho_in
  kho: add a struct for radix callbacks
  kho: add callback for table pages
  kho: add data argument to radix walk callback
  kho: allow early-boot usage of the KHO radix tree
  kho: allow destroying KHO radix tree
  kho: add kho_radix_init_tree()
  memblock: introduce MEMBLOCK_KHO_SCRATCH_EXT
  kho: extended scratch
  kho: return virtual address of mem_map
  mm/hugetlb: make bootmem allocation work with KHO

 include/linux/kexec_handover.h     |   1 +
 include/linux/kho_radix_tree.h     |  44 ++--
 include/linux/memblock.h           |  14 ++
 kernel/liveupdate/kexec_handover.c | 389 ++++++++++++++++++++++-------
 mm/hugetlb.c                       |  19 +-
 mm/memblock.c                      | 177 ++++++++++---
 mm/mm_init.c                       |   1 +
 7 files changed, 489 insertions(+), 156 deletions(-)


base-commit: eee13213401bafb7ffe3b447adffb1f570b9d813
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 01/12] kho: generalize radix tree APIs

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

The KHO radix tree is a data structure that can track the presence or
absence of an arbitrary key, with nothing inherently tied to KHO memory
preservation tracking. This was one of the design goals of the radix
tree. This was done to enable it to be re-used by other users of KHO.

Despite that, the radix tree APIs are very closely tied to KHO memory
preservation tracking. Adding a key is done by kho_radix_add_page(),
which encodes it as a page tracking operation and takes in PFN and
order. kho_radix_del_page() does the same. These functions encode the
key internally that goes into the radix tree. kho_radix_walk_tree() does
the same by baking the PFN and order into the callback arguments.

Generalize the APIs by taking the key directly and doing the encoding at
the callers. Rename the functions to kho_radix_add_key() and
kho_radix_del_key(). In practice, this removes a line each from the
functions and moves the encoding function call to the callers.
Similarly, update kho_radix_tree_walk_callback_t to take the key
directly.

To keep the naming convention clearer, rename
kho_radix_{encode,decode}_key() to kho_{encode,decode}_radix_key().

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kho_radix_tree.h     | 18 +++----
 kernel/liveupdate/kexec_handover.c | 76 ++++++++++++++----------------
 2 files changed, 42 insertions(+), 52 deletions(-)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index 84e918b96e53..f368f3b9f923 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -34,30 +34,24 @@ struct kho_radix_tree {
 	struct mutex lock; /* protects the tree's structure and root pointer */
 };
 
-typedef int (*kho_radix_tree_walk_callback_t)(phys_addr_t phys,
-					      unsigned int order);
+typedef int (*kho_radix_tree_walk_callback_t)(unsigned long key);
 
 #ifdef CONFIG_KEXEC_HANDOVER
 
-int kho_radix_add_page(struct kho_radix_tree *tree, unsigned long pfn,
-		       unsigned int order);
-
-void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
-			unsigned int order);
-
+int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
+void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
 			kho_radix_tree_walk_callback_t cb);
 
 #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
 
-static inline int kho_radix_add_page(struct kho_radix_tree *tree, long pfn,
-				     unsigned int order)
+static inline int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
 {
 	return -EOPNOTSUPP;
 }
 
-static inline void kho_radix_del_page(struct kho_radix_tree *tree,
-				      unsigned long pfn, unsigned int order) { }
+static inline void kho_radix_del_key(struct kho_radix_tree *tree,
+				     unsigned long key) { }
 
 static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
 				      kho_radix_tree_walk_callback_t cb)
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 33fcf848ef95..ba568d34c5b4 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -85,7 +85,7 @@ static struct kho_out kho_out = {
 };
 
 /**
- * kho_radix_encode_key - Encodes a physical address and order into a radix key.
+ * kho_encode_radix_key - Encodes a physical address and order into a radix key.
  * @phys: The physical address of the page.
  * @order: The order of the page.
  *
@@ -95,7 +95,7 @@ static struct kho_out kho_out = {
  *
  * Return: The encoded unsigned long radix key.
  */
-static unsigned long kho_radix_encode_key(phys_addr_t phys, unsigned int order)
+static unsigned long kho_encode_radix_key(phys_addr_t phys, unsigned int order)
 {
 	/* Order bits part */
 	unsigned long h = 1UL << (KHO_ORDER_0_LOG2 - order);
@@ -106,17 +106,17 @@ static unsigned long kho_radix_encode_key(phys_addr_t phys, unsigned int order)
 }
 
 /**
- * kho_radix_decode_key - Decodes a radix key back into a physical address and order.
+ * kho_decode_radix_key - Decodes a radix key back into a physical address and order.
  * @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(),
+ * This function reverses the encoding performed by kho_encode_radix_key(),
  * extracting the original physical address and page order from a given key.
  *
  * Return: The decoded physical address.
  */
-static phys_addr_t kho_radix_decode_key(unsigned long key, unsigned int *order)
+static phys_addr_t kho_decode_radix_key(unsigned long key, unsigned int *order)
 {
 	unsigned int order_bit = fls64(key);
 	phys_addr_t phys;
@@ -144,24 +144,21 @@ static unsigned long kho_radix_get_table_index(unsigned long key,
 }
 
 /**
- * kho_radix_add_page - Marks a page as preserved in the radix tree.
+ * kho_radix_add_key - Add a key to the radix tree.
  * @tree: The KHO radix tree.
- * @pfn: The page frame number of the page to preserve.
- * @order: The order of the page.
+ * @key: The key to add.
  *
- * 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.
+ * This function traverses the radix tree based on the key provided. It sets the
+ * corresponding bit in the leaf bitmap to mark the key as present. 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_tree *tree,
-		       unsigned long pfn, unsigned int order)
+int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
 {
 	/* 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 *anchor_node = NULL;
 	struct kho_radix_node *node = tree->root;
 	struct kho_radix_node *new_node;
@@ -224,22 +221,19 @@ int kho_radix_add_page(struct kho_radix_tree *tree,
 
 	return err;
 }
-EXPORT_SYMBOL_GPL(kho_radix_add_page);
+EXPORT_SYMBOL_GPL(kho_radix_add_key);
 
 /**
- * kho_radix_del_page - Removes a page's preservation status from the radix tree.
+ * kho_radix_del_key - Removes the key from the radix tree.
  * @tree: The KHO radix tree.
- * @pfn: The page frame number of the page to unpreserve.
- * @order: The order of the page.
+ * @key: The key to remove.
  *
  * 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.
+ * the key, effectively removing it from the tree. It does not free the tree's
+ * intermediate nodes, even if they become empty.
  */
-void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
-			unsigned int order)
+void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key)
 {
-	unsigned long key = kho_radix_encode_key(PFN_PHYS(pfn), order);
 	struct kho_radix_node *node = tree->root;
 	struct kho_radix_leaf *leaf;
 	unsigned int i, idx;
@@ -270,21 +264,18 @@ void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
 	idx = kho_radix_get_bitmap_index(key);
 	__clear_bit(idx, leaf->bitmap);
 }
-EXPORT_SYMBOL_GPL(kho_radix_del_page);
+EXPORT_SYMBOL_GPL(kho_radix_del_key);
 
 static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf,
 			       unsigned long key,
 			       kho_radix_tree_walk_callback_t cb)
 {
 	unsigned long *bitmap = (unsigned long *)leaf;
-	unsigned int order;
-	phys_addr_t phys;
 	unsigned int i;
 	int err;
 
 	for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
-		phys = kho_radix_decode_key(key | i, &order);
-		err = cb(phys, order);
+		err = cb(key | i);
 		if (err)
 			return err;
 	}
@@ -332,15 +323,14 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
 }
 
 /**
- * kho_radix_walk_tree - Traverses the radix tree and calls a callback for each preserved page.
+ * kho_radix_walk_tree - Traverses the radix tree and calls a callback for each key.
  * @tree: A pointer to the KHO radix tree to walk.
  * @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 physical address and order of the preserved page.
+ *      invoked for each key in the tree.
  *
  * This function walks the radix tree, searching from the specified top level
- * down to the lowest level (level 0). For each preserved page found, it invokes
- * the provided callback, passing the page's physical address and order.
+ * down to the lowest level (level 0). For each key found, it invokes the
+ * provided callback.
  *
  * Return: 0 if the walk completed the specified tree, or the non-zero return
  *         value from the callback that stopped the walk.
@@ -365,7 +355,8 @@ static void __kho_unpreserve(struct kho_radix_tree *tree,
 	while (pfn < end_pfn) {
 		order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
 
-		kho_radix_del_page(tree, pfn, order);
+		kho_radix_del_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
+							     order));
 
 		pfn += 1 << order;
 	}
@@ -498,13 +489,16 @@ static struct page *__init kho_get_preserved_page(phys_addr_t phys,
 	return pfn_to_page(pfn);
 }
 
-static int __init kho_preserved_memory_reserve(phys_addr_t phys,
-					       unsigned int order)
+static int __init kho_preserved_memory_reserve(unsigned long key)
 {
 	union kho_page_info info;
 	struct page *page;
+	unsigned int order;
+	phys_addr_t phys;
 	u64 sz;
 
+	phys = kho_decode_radix_key(key, &order);
+
 	sz = 1 << (order + PAGE_SHIFT);
 	page = kho_get_preserved_page(phys, order);
 
@@ -858,7 +852,8 @@ int kho_preserve_folio(struct folio *folio)
 	if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
 		return -EINVAL;
 
-	return kho_radix_add_page(tree, pfn, order);
+	return kho_radix_add_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
+							    order));
 }
 EXPORT_SYMBOL_GPL(kho_preserve_folio);
 
@@ -876,7 +871,7 @@ void kho_unpreserve_folio(struct folio *folio)
 	const unsigned long pfn = folio_pfn(folio);
 	const unsigned int order = folio_order(folio);
 
-	kho_radix_del_page(tree, pfn, order);
+	kho_radix_del_key(tree, kho_encode_radix_key(PFN_PHYS(pfn), order));
 }
 EXPORT_SYMBOL_GPL(kho_unpreserve_folio);
 
@@ -916,7 +911,8 @@ int kho_preserve_pages(struct page *page, unsigned long nr_pages)
 		while (pfn_to_nid(pfn) != pfn_to_nid(pfn + (1UL << order) - 1))
 			order--;
 
-		err = kho_radix_add_page(tree, pfn, order);
+		err = kho_radix_add_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
+								   order));
 		if (err) {
 			failed_pfn = pfn;
 			break;
-- 
2.54.0.545.g6539524ca2-goog

Re: [PATCH 01/12] kho: generalize radix tree APIs

[Pasha Tatashin]

On 04-29 15:39, Pratyush Yadav wrote:
> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
> 
> The KHO radix tree is a data structure that can track the presence or
> absence of an arbitrary key, with nothing inherently tied to KHO memory
> preservation tracking. This was one of the design goals of the radix
> tree. This was done to enable it to be re-used by other users of KHO.
> 
> Despite that, the radix tree APIs are very closely tied to KHO memory
> preservation tracking. Adding a key is done by kho_radix_add_page(),
> which encodes it as a page tracking operation and takes in PFN and
> order. kho_radix_del_page() does the same. These functions encode the
> key internally that goes into the radix tree. kho_radix_walk_tree() does
> the same by baking the PFN and order into the callback arguments.
> 
> Generalize the APIs by taking the key directly and doing the encoding at
> the callers. Rename the functions to kho_radix_add_key() and
> kho_radix_del_key(). In practice, this removes a line each from the
> functions and moves the encoding function call to the callers.
> Similarly, update kho_radix_tree_walk_callback_t to take the key
> directly.
> 
> To keep the naming convention clearer, rename
> kho_radix_{encode,decode}_key() to kho_{encode,decode}_radix_key().
> 
> Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>

Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com> 

> ---
>  include/linux/kho_radix_tree.h     | 18 +++----
>  kernel/liveupdate/kexec_handover.c | 76 ++++++++++++++----------------
>  2 files changed, 42 insertions(+), 52 deletions(-)
> 
> diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
> index 84e918b96e53..f368f3b9f923 100644
> --- a/include/linux/kho_radix_tree.h
> +++ b/include/linux/kho_radix_tree.h
> @@ -34,30 +34,24 @@ struct kho_radix_tree {
>  	struct mutex lock; /* protects the tree's structure and root pointer */
>  };
>  
> -typedef int (*kho_radix_tree_walk_callback_t)(phys_addr_t phys,
> -					      unsigned int order);
> +typedef int (*kho_radix_tree_walk_callback_t)(unsigned long key);
>  
>  #ifdef CONFIG_KEXEC_HANDOVER
>  
> -int kho_radix_add_page(struct kho_radix_tree *tree, unsigned long pfn,
> -		       unsigned int order);
> -
> -void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
> -			unsigned int order);
> -
> +int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
> +void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
>  int kho_radix_walk_tree(struct kho_radix_tree *tree,
>  			kho_radix_tree_walk_callback_t cb);
>  
>  #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
>  
> -static inline int kho_radix_add_page(struct kho_radix_tree *tree, long pfn,
> -				     unsigned int order)
> +static inline int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
>  {
>  	return -EOPNOTSUPP;
>  }
>  
> -static inline void kho_radix_del_page(struct kho_radix_tree *tree,
> -				      unsigned long pfn, unsigned int order) { }
> +static inline void kho_radix_del_key(struct kho_radix_tree *tree,
> +				     unsigned long key) { }
>  
>  static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
>  				      kho_radix_tree_walk_callback_t cb)
> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
> index 33fcf848ef95..ba568d34c5b4 100644
> --- a/kernel/liveupdate/kexec_handover.c
> +++ b/kernel/liveupdate/kexec_handover.c
> @@ -85,7 +85,7 @@ static struct kho_out kho_out = {
>  };
>  
>  /**
> - * kho_radix_encode_key - Encodes a physical address and order into a radix key.
> + * kho_encode_radix_key - Encodes a physical address and order into a radix key.
>   * @phys: The physical address of the page.
>   * @order: The order of the page.
>   *
> @@ -95,7 +95,7 @@ static struct kho_out kho_out = {
>   *
>   * Return: The encoded unsigned long radix key.
>   */
> -static unsigned long kho_radix_encode_key(phys_addr_t phys, unsigned int order)
> +static unsigned long kho_encode_radix_key(phys_addr_t phys, unsigned int order)
>  {
>  	/* Order bits part */
>  	unsigned long h = 1UL << (KHO_ORDER_0_LOG2 - order);
> @@ -106,17 +106,17 @@ static unsigned long kho_radix_encode_key(phys_addr_t phys, unsigned int order)
>  }
>  
>  /**
> - * kho_radix_decode_key - Decodes a radix key back into a physical address and order.
> + * kho_decode_radix_key - Decodes a radix key back into a physical address and order.
>   * @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(),
> + * This function reverses the encoding performed by kho_encode_radix_key(),
>   * extracting the original physical address and page order from a given key.
>   *
>   * Return: The decoded physical address.
>   */
> -static phys_addr_t kho_radix_decode_key(unsigned long key, unsigned int *order)
> +static phys_addr_t kho_decode_radix_key(unsigned long key, unsigned int *order)
>  {
>  	unsigned int order_bit = fls64(key);
>  	phys_addr_t phys;
> @@ -144,24 +144,21 @@ static unsigned long kho_radix_get_table_index(unsigned long key,
>  }
>  
>  /**
> - * kho_radix_add_page - Marks a page as preserved in the radix tree.
> + * kho_radix_add_key - Add a key to the radix tree.
>   * @tree: The KHO radix tree.
> - * @pfn: The page frame number of the page to preserve.
> - * @order: The order of the page.
> + * @key: The key to add.
>   *
> - * 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.
> + * This function traverses the radix tree based on the key provided. It sets the
> + * corresponding bit in the leaf bitmap to mark the key as present. 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_tree *tree,
> -		       unsigned long pfn, unsigned int order)
> +int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
>  {
>  	/* 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 *anchor_node = NULL;
>  	struct kho_radix_node *node = tree->root;
>  	struct kho_radix_node *new_node;
> @@ -224,22 +221,19 @@ int kho_radix_add_page(struct kho_radix_tree *tree,
>  
>  	return err;
>  }
> -EXPORT_SYMBOL_GPL(kho_radix_add_page);
> +EXPORT_SYMBOL_GPL(kho_radix_add_key);
>  
>  /**
> - * kho_radix_del_page - Removes a page's preservation status from the radix tree.
> + * kho_radix_del_key - Removes the key from the radix tree.
>   * @tree: The KHO radix tree.
> - * @pfn: The page frame number of the page to unpreserve.
> - * @order: The order of the page.
> + * @key: The key to remove.
>   *
>   * 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.
> + * the key, effectively removing it from the tree. It does not free the tree's
> + * intermediate nodes, even if they become empty.
>   */
> -void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
> -			unsigned int order)
> +void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key)
>  {
> -	unsigned long key = kho_radix_encode_key(PFN_PHYS(pfn), order);
>  	struct kho_radix_node *node = tree->root;
>  	struct kho_radix_leaf *leaf;
>  	unsigned int i, idx;
> @@ -270,21 +264,18 @@ void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
>  	idx = kho_radix_get_bitmap_index(key);
>  	__clear_bit(idx, leaf->bitmap);
>  }
> -EXPORT_SYMBOL_GPL(kho_radix_del_page);
> +EXPORT_SYMBOL_GPL(kho_radix_del_key);
>  
>  static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf,
>  			       unsigned long key,
>  			       kho_radix_tree_walk_callback_t cb)
>  {
>  	unsigned long *bitmap = (unsigned long *)leaf;
> -	unsigned int order;
> -	phys_addr_t phys;
>  	unsigned int i;
>  	int err;
>  
>  	for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
> -		phys = kho_radix_decode_key(key | i, &order);
> -		err = cb(phys, order);
> +		err = cb(key | i);
>  		if (err)
>  			return err;
>  	}
> @@ -332,15 +323,14 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
>  }
>  
>  /**
> - * kho_radix_walk_tree - Traverses the radix tree and calls a callback for each preserved page.
> + * kho_radix_walk_tree - Traverses the radix tree and calls a callback for each key.
>   * @tree: A pointer to the KHO radix tree to walk.
>   * @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 physical address and order of the preserved page.
> + *      invoked for each key in the tree.
>   *
>   * This function walks the radix tree, searching from the specified top level
> - * down to the lowest level (level 0). For each preserved page found, it invokes
> - * the provided callback, passing the page's physical address and order.
> + * down to the lowest level (level 0). For each key found, it invokes the
> + * provided callback.
>   *
>   * Return: 0 if the walk completed the specified tree, or the non-zero return
>   *         value from the callback that stopped the walk.
> @@ -365,7 +355,8 @@ static void __kho_unpreserve(struct kho_radix_tree *tree,
>  	while (pfn < end_pfn) {
>  		order = min(count_trailing_zeros(pfn), ilog2(end_pfn - pfn));
>  
> -		kho_radix_del_page(tree, pfn, order);
> +		kho_radix_del_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
> +							     order));
>  
>  		pfn += 1 << order;
>  	}
> @@ -498,13 +489,16 @@ static struct page *__init kho_get_preserved_page(phys_addr_t phys,
>  	return pfn_to_page(pfn);
>  }
>  
> -static int __init kho_preserved_memory_reserve(phys_addr_t phys,
> -					       unsigned int order)
> +static int __init kho_preserved_memory_reserve(unsigned long key)
>  {
>  	union kho_page_info info;
>  	struct page *page;
> +	unsigned int order;
> +	phys_addr_t phys;
>  	u64 sz;
>  
> +	phys = kho_decode_radix_key(key, &order);
> +
>  	sz = 1 << (order + PAGE_SHIFT);
>  	page = kho_get_preserved_page(phys, order);
>  
> @@ -858,7 +852,8 @@ int kho_preserve_folio(struct folio *folio)
>  	if (WARN_ON(kho_scratch_overlap(pfn << PAGE_SHIFT, PAGE_SIZE << order)))
>  		return -EINVAL;
>  
> -	return kho_radix_add_page(tree, pfn, order);
> +	return kho_radix_add_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
> +							    order));
>  }
>  EXPORT_SYMBOL_GPL(kho_preserve_folio);
>  
> @@ -876,7 +871,7 @@ void kho_unpreserve_folio(struct folio *folio)
>  	const unsigned long pfn = folio_pfn(folio);
>  	const unsigned int order = folio_order(folio);
>  
> -	kho_radix_del_page(tree, pfn, order);
> +	kho_radix_del_key(tree, kho_encode_radix_key(PFN_PHYS(pfn), order));
>  }
>  EXPORT_SYMBOL_GPL(kho_unpreserve_folio);
>  
> @@ -916,7 +911,8 @@ int kho_preserve_pages(struct page *page, unsigned long nr_pages)
>  		while (pfn_to_nid(pfn) != pfn_to_nid(pfn + (1UL << order) - 1))
>  			order--;
>  
> -		err = kho_radix_add_page(tree, pfn, order);
> +		err = kho_radix_add_key(tree, kho_encode_radix_key(PFN_PHYS(pfn),
> +								   order));
>  		if (err) {
>  			failed_pfn = pfn;
>  			break;
> -- 
> 2.54.0.545.g6539524ca2-goog
> 

Re: [PATCH 01/12] kho: generalize radix tree APIs

[Jork Loeser]

On Wed, 29 Apr 2026, Pratyush Yadav wrote:

> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
>
> The KHO radix tree is a data structure that can track the presence or
> absence of an arbitrary key, with nothing inherently tied to KHO memory
> preservation tracking. This was one of the design goals of the radix
> tree. This was done to enable it to be re-used by other users of KHO.

"Arbitrary key": Not quite the complete 64-bits, rather 64 - PAGE_SIZE, 
correct?

> + * kho_radix_add_key - Add a key to the radix tree.
>  * @tree: The KHO radix tree.
> + * @key: The key to add.
>  *
> + * This function traverses the radix tree based on the key provided. It sets the
> + * corresponding bit in the leaf bitmap to mark the key as present. If
> + * intermediate nodes do not exist along the path, they are allocated and added
> + * to the tree.

Consider adding a note on the key-width limitation.

Best,
Jork

Re: [PATCH 01/12] kho: generalize radix tree APIs

[Pratyush Yadav]

On Tue, May 05 2026, Jork Loeser wrote:

> On Wed, 29 Apr 2026, Pratyush Yadav wrote:
>
>> From: "Pratyush Yadav (Google)" <pratyush@kernel.org>
>>
>> The KHO radix tree is a data structure that can track the presence or
>> absence of an arbitrary key, with nothing inherently tied to KHO memory
>> preservation tracking. This was one of the design goals of the radix
>> tree. This was done to enable it to be re-used by other users of KHO.
>
> "Arbitrary key": Not quite the complete 64-bits, rather 64 - PAGE_SIZE, correct?

Right, 64 - PAGE_SHIFT.

>
>> + * kho_radix_add_key - Add a key to the radix tree.
>>  * @tree: The KHO radix tree.
>> + * @key: The key to add.
>>  *
>> + * This function traverses the radix tree based on the key provided. It sets the
>> + * corresponding bit in the leaf bitmap to mark the key as present. If
>> + * intermediate nodes do not exist along the path, they are allocated and added
>> + * to the tree.
>
> Consider adding a note on the key-width limitation.

I think adding a runtime check would also be a good idea here.

-- 
Regards,
Pratyush Yadav

[PATCH 02/12] kho: store incoming radix tree in kho_in

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

This allows other functions to also use the radix tree. While at it,
also use kho_get_mem_map_phys() instead of duplicating the code to get
the radix tree root from the FDT.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 27 ++++++++-------------------
 1 file changed, 8 insertions(+), 19 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index ba568d34c5b4..5758dc6fab5d 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -1294,6 +1294,7 @@ struct kho_in {
 	char previous_release[__NEW_UTS_LEN + 1];
 	u32 kexec_count;
 	struct kho_debugfs dbg;
+	struct kho_radix_tree radix_tree;
 };
 
 static struct kho_in kho_in = {
@@ -1373,24 +1374,10 @@ EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
 
 static int __init kho_mem_retrieve(const void *fdt)
 {
-	struct kho_radix_tree tree;
-	const phys_addr_t *mem;
-	int len;
-
-	/* Retrieve the KHO radix tree from passed-in FDT. */
-	mem = fdt_getprop(fdt, 0, KHO_FDT_MEMORY_MAP_PROP_NAME, &len);
-
-	if (!mem || len != sizeof(*mem)) {
-		pr_err("failed to get preserved KHO memory tree\n");
-		return -ENOENT;
-	}
-
-	if (!*mem)
-		return -EINVAL;
-
-	tree.root = phys_to_virt(*mem);
-	mutex_init(&tree.lock);
-	return kho_radix_walk_tree(&tree, kho_preserved_memory_reserve);
+	kho_in.radix_tree.root = phys_to_virt(kho_get_mem_map_phys(fdt));
+	mutex_init(&kho_in.radix_tree.lock);
+	return kho_radix_walk_tree(&kho_in.radix_tree,
+				   kho_preserved_memory_reserve);
 }
 
 static __init int kho_out_fdt_setup(void)
@@ -1597,8 +1584,10 @@ void __init kho_memory_init(void)
 	if (kho_in.scratch_phys) {
 		kho_scratch = phys_to_virt(kho_in.scratch_phys);
 
-		if (kho_mem_retrieve(kho_get_fdt()))
+		if (kho_mem_retrieve(kho_get_fdt())) {
 			kho_in.fdt_phys = 0;
+			kho_in.radix_tree.root = NULL;
+		}
 	} else {
 		kho_reserve_scratch();
 	}
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 03/12] kho: add a struct for radix callbacks

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

A future commit will add more callbacks for the KHO radix tree. Add a
struct for collecting the callbacks.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kho_radix_tree.h     | 15 ++++++++++++---
 kernel/liveupdate/kexec_handover.c | 29 ++++++++++++++++-------------
 2 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index f368f3b9f923..030da6399d28 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -34,14 +34,23 @@ struct kho_radix_tree {
 	struct mutex lock; /* protects the tree's structure and root pointer */
 };
 
-typedef int (*kho_radix_tree_walk_callback_t)(unsigned long key);
+/**
+ * struct kho_radix_walk_cb - Callbacks for KHO radix tree walk.
+ * @key:      Called on each present key in the radix tree.
+ *
+ * For each callback, a return value of 0 continues the walk and a non-zero
+ * return value is directly returned to the caller.
+ */
+struct kho_radix_walk_cb {
+	int (*key)(unsigned long key);
+};
 
 #ifdef CONFIG_KEXEC_HANDOVER
 
 int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
 void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
-			kho_radix_tree_walk_callback_t cb);
+			const struct kho_radix_walk_cb *cb);
 
 #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
 
@@ -54,7 +63,7 @@ static inline void kho_radix_del_key(struct kho_radix_tree *tree,
 				     unsigned long key) { }
 
 static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
-				      kho_radix_tree_walk_callback_t cb)
+				      const struct kho_radix_walk_cb *cb)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 5758dc6fab5d..4a5d1b47799c 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -266,16 +266,18 @@ void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key)
 }
 EXPORT_SYMBOL_GPL(kho_radix_del_key);
 
-static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf,
-			       unsigned long key,
-			       kho_radix_tree_walk_callback_t cb)
+static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
+			       const struct kho_radix_walk_cb *cb)
 {
 	unsigned long *bitmap = (unsigned long *)leaf;
 	unsigned int i;
 	int err;
 
+	if (!cb->key)
+		return 0;
+
 	for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
-		err = cb(key | i);
+		err = cb->key(key | i);
 		if (err)
 			return err;
 	}
@@ -285,7 +287,7 @@ static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf,
 
 static int __kho_radix_walk_tree(struct kho_radix_node *root,
 				 unsigned int level, unsigned long start,
-				 kho_radix_tree_walk_callback_t cb)
+				 const struct kho_radix_walk_cb *cb)
 {
 	struct kho_radix_node *node;
 	struct kho_radix_leaf *leaf;
@@ -325,18 +327,16 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
 /**
  * kho_radix_walk_tree - Traverses the radix tree and calls a callback for each key.
  * @tree: A pointer to the KHO radix tree to walk.
- * @cb: A callback function of type kho_radix_tree_walk_callback_t that will be
- *      invoked for each key in the tree.
+ * @cb:   Set of callbacks to be invoked during the tree walk.
  *
- * This function walks the radix tree, searching from the specified top level
- * down to the lowest level (level 0). For each key found, it invokes the
- * provided callback.
+ * This function walks the radix tree, searching from the top level down to the
+ * lowest level (level 0), invoking the appropriate callbacks.
  *
  * Return: 0 if the walk completed the specified tree, or the non-zero return
  *         value from the callback that stopped the walk.
  */
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
-			kho_radix_tree_walk_callback_t cb)
+			const struct kho_radix_walk_cb *cb)
 {
 	if (WARN_ON_ONCE(!tree->root))
 		return -EINVAL;
@@ -1374,10 +1374,13 @@ EXPORT_SYMBOL_GPL(kho_retrieve_subtree);
 
 static int __init kho_mem_retrieve(const void *fdt)
 {
+	const struct kho_radix_walk_cb cb = {
+		.key = kho_preserved_memory_reserve,
+	};
+
 	kho_in.radix_tree.root = phys_to_virt(kho_get_mem_map_phys(fdt));
 	mutex_init(&kho_in.radix_tree.lock);
-	return kho_radix_walk_tree(&kho_in.radix_tree,
-				   kho_preserved_memory_reserve);
+	return kho_radix_walk_tree(&kho_in.radix_tree, &cb);
 }
 
 static __init int kho_out_fdt_setup(void)
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 04/12] kho: add callback for table pages

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

The KHO memory preservation radix tree does not mark the table pages
themselves as scratch. This is done to avoid a circular dependency where
preserving a page can lead of allocating other preserved pages. This
means any walker looking for free ranges of memory outside of scratch
areas will ignore the table

Add a table callback that is invoked for each table page. The callback
is given the physical address of the table page.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kho_radix_tree.h     |  3 +++
 kernel/liveupdate/kexec_handover.c | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index 030da6399d28..fe7151d89361 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -37,12 +37,15 @@ struct kho_radix_tree {
 /**
  * struct kho_radix_walk_cb - Callbacks for KHO radix tree walk.
  * @key:      Called on each present key in the radix tree.
+ * @table:    Called on each table of the radix tree itself. Receives the
+ *            physical address of the page containing the table.
  *
  * For each callback, a return value of 0 continues the walk and a non-zero
  * return value is directly returned to the caller.
  */
 struct kho_radix_walk_cb {
 	int (*key)(unsigned long key);
+	int (*table)(phys_addr_t phys);
 };
 
 #ifdef CONFIG_KEXEC_HANDOVER
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 4a5d1b47799c..94ca831b41c9 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -273,6 +273,12 @@ static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
 	unsigned int i;
 	int err;
 
+	if (cb->table) {
+		err = cb->table(virt_to_phys(leaf));
+		if (err)
+			return err;
+	}
+
 	if (!cb->key)
 		return 0;
 
@@ -295,6 +301,12 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
 	unsigned int shift;
 	int err;
 
+	if (cb->table) {
+		err = cb->table(virt_to_phys(root));
+		if (err)
+			return err;
+	}
+
 	for (i = 0; i < PAGE_SIZE / sizeof(phys_addr_t); i++) {
 		if (!root->table[i])
 			continue;
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 05/12] kho: add data argument to radix walk callback

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Add an opaque data pointer argument to kho_radix_walk_cb_t. This can be
used for callers to pass extra information to the callback.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kho_radix_tree.h     |  8 ++++----
 kernel/liveupdate/kexec_handover.c | 24 +++++++++++++-----------
 2 files changed, 17 insertions(+), 15 deletions(-)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index fe7151d89361..6c0f7d82716b 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -44,8 +44,8 @@ struct kho_radix_tree {
  * return value is directly returned to the caller.
  */
 struct kho_radix_walk_cb {
-	int (*key)(unsigned long key);
-	int (*table)(phys_addr_t phys);
+	int (*key)(unsigned long key, void *data);
+	int (*table)(phys_addr_t phys, void *data);
 };
 
 #ifdef CONFIG_KEXEC_HANDOVER
@@ -53,7 +53,7 @@ struct kho_radix_walk_cb {
 int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
 void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
-			const struct kho_radix_walk_cb *cb);
+			const struct kho_radix_walk_cb *cb, void *data);
 
 #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
 
@@ -66,7 +66,7 @@ static inline void kho_radix_del_key(struct kho_radix_tree *tree,
 				     unsigned long key) { }
 
 static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
-				      const struct kho_radix_walk_cb *cb)
+				      const struct kho_radix_walk_cb *cb, void *data)
 {
 	return -EOPNOTSUPP;
 }
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 94ca831b41c9..d0a4f78eccfe 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -267,14 +267,14 @@ void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key)
 EXPORT_SYMBOL_GPL(kho_radix_del_key);
 
 static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
-			       const struct kho_radix_walk_cb *cb)
+			       const struct kho_radix_walk_cb *cb, void *data)
 {
 	unsigned long *bitmap = (unsigned long *)leaf;
 	unsigned int i;
 	int err;
 
 	if (cb->table) {
-		err = cb->table(virt_to_phys(leaf));
+		err = cb->table(virt_to_phys(leaf), data);
 		if (err)
 			return err;
 	}
@@ -283,7 +283,7 @@ static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
 		return 0;
 
 	for_each_set_bit(i, bitmap, PAGE_SIZE * BITS_PER_BYTE) {
-		err = cb->key(key | i);
+		err = cb->key(key | i, data);
 		if (err)
 			return err;
 	}
@@ -293,7 +293,7 @@ static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
 
 static int __kho_radix_walk_tree(struct kho_radix_node *root,
 				 unsigned int level, unsigned long start,
-				 const struct kho_radix_walk_cb *cb)
+				 const struct kho_radix_walk_cb *cb, void *data)
 {
 	struct kho_radix_node *node;
 	struct kho_radix_leaf *leaf;
@@ -302,7 +302,7 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
 	int err;
 
 	if (cb->table) {
-		err = cb->table(virt_to_phys(root));
+		err = cb->table(virt_to_phys(root), data);
 		if (err)
 			return err;
 	}
@@ -323,10 +323,10 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
 			 * node is pointing to the level 0 bitmap.
 			 */
 			leaf = (struct kho_radix_leaf *)node;
-			err = kho_radix_walk_leaf(leaf, key, cb);
+			err = kho_radix_walk_leaf(leaf, key, cb, data);
 		} else {
 			err  = __kho_radix_walk_tree(node, level - 1,
-						     key, cb);
+						     key, cb, data);
 		}
 
 		if (err)
@@ -340,6 +340,7 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
  * kho_radix_walk_tree - Traverses the radix tree and calls a callback for each key.
  * @tree: A pointer to the KHO radix tree to walk.
  * @cb:   Set of callbacks to be invoked during the tree walk.
+ * @data: Opaque data pointer passed to each callback in @cb.
  *
  * This function walks the radix tree, searching from the top level down to the
  * lowest level (level 0), invoking the appropriate callbacks.
@@ -348,14 +349,15 @@ static int __kho_radix_walk_tree(struct kho_radix_node *root,
  *         value from the callback that stopped the walk.
  */
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
-			const struct kho_radix_walk_cb *cb)
+			const struct kho_radix_walk_cb *cb, void *data)
 {
 	if (WARN_ON_ONCE(!tree->root))
 		return -EINVAL;
 
 	guard(mutex)(&tree->lock);
 
-	return __kho_radix_walk_tree(tree->root, KHO_TREE_MAX_DEPTH - 1, 0, cb);
+	return __kho_radix_walk_tree(tree->root, KHO_TREE_MAX_DEPTH - 1, 0, cb,
+				     data);
 }
 EXPORT_SYMBOL_GPL(kho_radix_walk_tree);
 
@@ -501,7 +503,7 @@ static struct page *__init kho_get_preserved_page(phys_addr_t phys,
 	return pfn_to_page(pfn);
 }
 
-static int __init kho_preserved_memory_reserve(unsigned long key)
+static int __init kho_preserved_memory_reserve(unsigned long key, void *data)
 {
 	union kho_page_info info;
 	struct page *page;
@@ -1392,7 +1394,7 @@ static int __init kho_mem_retrieve(const void *fdt)
 
 	kho_in.radix_tree.root = phys_to_virt(kho_get_mem_map_phys(fdt));
 	mutex_init(&kho_in.radix_tree.lock);
-	return kho_radix_walk_tree(&kho_in.radix_tree, &cb);
+	return kho_radix_walk_tree(&kho_in.radix_tree, &cb, NULL);
 }
 
 static __init int kho_out_fdt_setup(void)
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 06/12] kho: allow early-boot usage of the KHO radix tree

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

The KHO radix tree allocates memory for table pages from the buddy
allocator using get_zeroed_page(). This is not available in early boot
when memblock is still active.

Using the radix tree in early boot is useful for KHO to track metadata
about its memory. One such example is for tracking free blocks for
memory allocation when scratch runs out of space. This feature will be
added in the following commits.

Add kho_radix_{alloc,free}_node() which allocate and free the table
pages. They use slab_is_available() to decide which allocator to use.
While slab_is_available() indicates availability of the slab allocator,
it gets initialized right before buddy so it serves the same practical
purpose.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index d0a4f78eccfe..47f7c4a2865e 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -143,6 +143,26 @@ static unsigned long kho_radix_get_table_index(unsigned long key,
 	return (key >> s) % (1 << KHO_TABLE_SIZE_LOG2);
 }
 
+static void __ref *kho_radix_alloc_node(void)
+{
+	struct kho_radix_node *node;
+
+	if (slab_is_available())
+		node = (struct kho_radix_node *)get_zeroed_page(GFP_KERNEL);
+	else
+		node = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
+
+	return node;
+}
+
+static void __ref kho_radix_free_node(struct kho_radix_node *node)
+{
+	if (slab_is_available())
+		free_page((unsigned long)node);
+	else
+		memblock_free(node, PAGE_SIZE);
+}
+
 /**
  * kho_radix_add_key - Add a key to the radix tree.
  * @tree: The KHO radix tree.
@@ -183,7 +203,7 @@ int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
 		}
 
 		/* Next node is empty, create a new node for it */
-		new_node = (struct kho_radix_node *)get_zeroed_page(GFP_KERNEL);
+		new_node = kho_radix_alloc_node();
 		if (!new_node) {
 			err = -ENOMEM;
 			goto err_free_nodes;
@@ -214,7 +234,7 @@ int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
 err_free_nodes:
 	for (i = KHO_TREE_MAX_DEPTH - 1; i > 0; i--) {
 		if (intermediate_nodes[i])
-			free_page((unsigned long)intermediate_nodes[i]);
+			kho_radix_free_node(intermediate_nodes[i]);
 	}
 	if (anchor_node)
 		anchor_node->table[anchor_idx] = 0;
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 07/12] kho: allow destroying KHO radix tree

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Add kho_radix_destroy_tree() which allows destroying the radix tree and
freeing all its pages.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kho_radix_tree.h     |  3 +++
 kernel/liveupdate/kexec_handover.c | 34 ++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index 6c0f7d82716b..617395a6647a 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -54,6 +54,7 @@ int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
 void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
 			const struct kho_radix_walk_cb *cb, void *data);
+void kho_radix_destroy_tree(struct kho_radix_tree *tree);
 
 #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
 
@@ -71,6 +72,8 @@ static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
 	return -EOPNOTSUPP;
 }
 
+static inline void kho_radix_destroy_tree(struct kho_radix_tree *tree) { }
+
 #endif /* #ifdef CONFIG_KEXEC_HANDOVER */
 
 #endif	/* _LINUX_KHO_RADIX_TREE_H */
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 47f7c4a2865e..29479534f65d 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -286,6 +286,40 @@ void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key)
 }
 EXPORT_SYMBOL_GPL(kho_radix_del_key);
 
+static void __kho_radix_destroy_tree(struct kho_radix_node *root,
+				     unsigned int level)
+{
+	unsigned long i;
+
+	if (level == 0) {
+		kho_radix_free_node(root);
+		return;
+	}
+
+	for (i = 0; i < PAGE_SIZE / sizeof(phys_addr_t); i++) {
+		if (root->table[i])
+			__kho_radix_destroy_tree(phys_to_virt(root->table[i]),
+						 level - 1);
+	}
+
+	kho_radix_free_node(root);
+}
+
+/**
+ * kho_radix_destroy_tree - Destroy the radix tree
+ * @tree: The radix tree to destroy
+ *
+ * Walk @tree and free all its nodes.
+ */
+void kho_radix_destroy_tree(struct kho_radix_tree *tree)
+{
+	if (!tree->root)
+		return;
+
+	__kho_radix_destroy_tree(tree->root, KHO_TREE_MAX_DEPTH - 1);
+}
+EXPORT_SYMBOL_GPL(kho_radix_destroy_tree);
+
 static int kho_radix_walk_leaf(struct kho_radix_leaf *leaf, unsigned long key,
 			       const struct kho_radix_walk_cb *cb, void *data)
 {
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 08/12] kho: add kho_radix_init_tree()

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Move the initialization logic of the radix tree into
kho_radix_init_tree() instead of having users open-code it. Makes the
boundaries cleaner and reduces code duplication when a new user of the
radix tree will be added in a future commit.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kho_radix_tree.h     |  7 ++++++
 kernel/liveupdate/kexec_handover.c | 37 ++++++++++++++++++++++++++++--
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index 617395a6647a..c0840ecb230c 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -54,6 +54,7 @@ int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
 void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
 			const struct kho_radix_walk_cb *cb, void *data);
+int kho_radix_init_tree(struct kho_radix_tree *tree, struct kho_radix_node *root);
 void kho_radix_destroy_tree(struct kho_radix_tree *tree);
 
 #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
@@ -72,6 +73,12 @@ static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
 	return -EOPNOTSUPP;
 }
 
+static inline int kho_radix_init_tree(struct kho_radix_tree *tree,
+				      struct kho_radix_node *root)
+{
+	return 0;
+}
+
 static inline void kho_radix_destroy_tree(struct kho_radix_tree *tree) { }
 
 #endif /* #ifdef CONFIG_KEXEC_HANDOVER */
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 29479534f65d..1a04e089f779 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -305,6 +305,34 @@ static void __kho_radix_destroy_tree(struct kho_radix_node *root,
 	kho_radix_free_node(root);
 }
 
+/**
+ * kho_radix_init_tree - initialize the radix tree.
+ * @tree:   the tree to initialize.
+ * @root:   root table of the radix tree.
+ *
+ * Initialize the radix tree with the given root node. If root is %NULL, an
+ * empty root table is allocated. If root is not %NULL, it is the caller's
+ * responsibility to make sure the root is valid and in the correct format.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int kho_radix_init_tree(struct kho_radix_tree *tree, struct kho_radix_node *root)
+{
+	/* Already initialized. */
+	if (tree->root)
+		return 0;
+
+	if (!root)
+		root = kho_radix_alloc_node();
+	if (!root)
+		return -ENOMEM;
+
+	tree->root = root;
+	mutex_init(&tree->lock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kho_radix_init_tree);
+
 /**
  * kho_radix_destroy_tree - Destroy the radix tree
  * @tree: The radix tree to destroy
@@ -1445,9 +1473,14 @@ static int __init kho_mem_retrieve(const void *fdt)
 	const struct kho_radix_walk_cb cb = {
 		.key = kho_preserved_memory_reserve,
 	};
+	phys_addr_t mem_map_phys;
+	int err;
+
+	mem_map_phys = kho_get_mem_map_phys(fdt);
+	err = kho_radix_init_tree(&kho_in.radix_tree, phys_to_virt(mem_map_phys));
+	if (err)
+		return err;
 
-	kho_in.radix_tree.root = phys_to_virt(kho_get_mem_map_phys(fdt));
-	mutex_init(&kho_in.radix_tree.lock);
 	return kho_radix_walk_tree(&kho_in.radix_tree, &cb, NULL);
 }
 
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 09/12] memblock: introduce MEMBLOCK_KHO_SCRATCH_EXT

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

In the upcoming commits, the KHO will learn how to discover free blocks
of memory by walking the KHO radix tree. It will then mark those regions
as scratch to allow memory allocation in case scratch runs low.

To differentiate the extended scratch areas from the main scratch areas,
introduce MEMBLOCK_KHO_SCRATCH_EXT. Use it when choosing memblock flags
for allocations during scratch-only. Teach should_skip_region() to check
for both flags before deciding if the region should be skipped.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---

Notes:
    Checkpatch complains about no space after MEMBLOCK_KHO_SCRATCH_EXT in
    the declaration, but doing so makes it nicely align with all the other
    numbers. Mike, if you'd like I can add some whitespace.

 include/linux/memblock.h | 10 ++++++++++
 mm/memblock.c            | 41 ++++++++++++++++++++++++++++++++++------
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 5afcd99aa8c1..4f535ca4947a 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -51,6 +51,9 @@ extern unsigned long long max_possible_pfn;
  * memory reservations yet, so we get scratch memory from the previous
  * kernel that we know is good to use. It is the only memory that
  * allocations may happen from in this phase.
+ * @MEMBLOCK_KHO_SCRATCH_EXT: same as MEMBLOCK_KHO_SCRATCH but was discovered at
+ * boot time by finding gaps in preserved memory instead of being passed from
+ * previous kernel. Does not get passed to the next kernel.
  */
 enum memblock_flags {
 	MEMBLOCK_NONE		= 0x0,	/* No special request */
@@ -61,6 +64,7 @@ enum memblock_flags {
 	MEMBLOCK_RSRV_NOINIT	= 0x10,	/* don't initialize struct pages */
 	MEMBLOCK_RSRV_KERN	= 0x20,	/* memory reserved for kernel use */
 	MEMBLOCK_KHO_SCRATCH	= 0x40,	/* scratch memory for kexec handover */
+	MEMBLOCK_KHO_SCRATCH_EXT= 0x80, /* extended scratch memory for KHO */
 };
 
 /**
@@ -157,6 +161,7 @@ int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size);
 int memblock_reserved_mark_kern(phys_addr_t base, phys_addr_t size);
 int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size);
+int memblock_mark_kho_scratch_ext(phys_addr_t base, phys_addr_t size);
 int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size);
 
 void memblock_free(void *ptr, size_t size);
@@ -304,6 +309,11 @@ static inline bool memblock_is_kho_scratch(struct memblock_region *m)
 	return m->flags & MEMBLOCK_KHO_SCRATCH;
 }
 
+static inline bool memblock_is_kho_scratch_ext(struct memblock_region *m)
+{
+	return m->flags & MEMBLOCK_KHO_SCRATCH_EXT;
+}
+
 int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
 			    unsigned long  *end_pfn);
 void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
diff --git a/mm/memblock.c b/mm/memblock.c
index 01a962681726..79443e004361 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -182,7 +182,7 @@ static enum memblock_flags __init_memblock choose_memblock_flags(void)
 {
 	/* skip non-scratch memory for kho early boot allocations */
 	if (kho_scratch_only)
-		return MEMBLOCK_KHO_SCRATCH;
+		return MEMBLOCK_KHO_SCRATCH | MEMBLOCK_KHO_SCRATCH_EXT;
 
 	return system_has_some_mirror ? MEMBLOCK_MIRROR : MEMBLOCK_NONE;
 }
@@ -1178,8 +1178,9 @@ int __init_memblock memblock_reserved_mark_kern(phys_addr_t base, phys_addr_t si
  * @base: the base phys addr of the region
  * @size: the size of the region
  *
- * Only memory regions marked with %MEMBLOCK_KHO_SCRATCH will be considered
- * for allocations during early boot with kexec handover.
+ * Only memory regions marked with %MEMBLOCK_KHO_SCRATCH or
+ * %MEMBLOCK_KHO_SCRATCH_EXT will be considered for allocations during early
+ * boot with kexec handover.
  *
  * Return: 0 on success, -errno on failure.
  */
@@ -1203,6 +1204,23 @@ __init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
 				    MEMBLOCK_KHO_SCRATCH);
 }
 
+/**
+ * memblock_mark_kho_scratch_ext - Mark a memory region as MEMBLOCK_KHO_SCRATCH_EXT.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Only memory regions marked with %MEMBLOCK_KHO_SCRATCH or
+ * %MEMBLOCK_KHO_SCRATCH_EXT will be considered for allocations during early
+ * boot with kexec handover.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+__init int memblock_mark_kho_scratch_ext(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(&memblock.memory, base, size, 1,
+				    MEMBLOCK_KHO_SCRATCH_EXT);
+}
+
 static bool should_skip_region(struct memblock_type *type,
 			       struct memblock_region *m,
 			       int nid, int flags)
@@ -1236,10 +1254,20 @@ static bool should_skip_region(struct memblock_type *type,
 
 	/*
 	 * In early alloc during kexec handover, we can only consider
-	 * MEMBLOCK_KHO_SCRATCH regions for the allocations
+	 * MEMBLOCK_KHO_SCRATCH or MEMBLOCK_KHO_SCRATCH_EXT regions for the
+	 * allocations.
 	 */
-	if ((flags & MEMBLOCK_KHO_SCRATCH) && !memblock_is_kho_scratch(m))
-		return true;
+	if (flags & (MEMBLOCK_KHO_SCRATCH | MEMBLOCK_KHO_SCRATCH_EXT)) {
+		bool skip = true;
+
+		if ((flags & MEMBLOCK_KHO_SCRATCH) && memblock_is_kho_scratch(m))
+			skip = false;
+
+		if ((flags & MEMBLOCK_KHO_SCRATCH_EXT) && memblock_is_kho_scratch_ext(m))
+			skip = false;
+
+		return skip;
+	}
 
 	return false;
 }
@@ -2799,6 +2827,7 @@ static const char * const flagname[] = {
 	[ilog2(MEMBLOCK_RSRV_NOINIT)] = "RSV_NIT",
 	[ilog2(MEMBLOCK_RSRV_KERN)] = "RSV_KERN",
 	[ilog2(MEMBLOCK_KHO_SCRATCH)] = "KHO_SCRATCH",
+	[ilog2(MEMBLOCK_KHO_SCRATCH_EXT)] = "KHO_SCRATCH_EXT",
 };
 
 static int memblock_debug_show(struct seq_file *m, void *private)
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 10/12] kho: extended scratch

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Motivation
==========

The scratch space is allocated by the first kernel in the KHO chain, and
is reused by all subsequent kernels. The size of the space is either set
via the commandline by the system administrator or by calculating the
amount of memory used by the kernel and adding a multiplier. In either
case, the scratch space is a heuristic and is liable to fill up and fail
allocation if a kernel uses more memory than expected.

In addition, gigantic huge pages (usually 1 GiB) are allocated via
memblock, and in a KHO boot that memory comes from the scratch space. In
hypervisors it is common to dedicate a major part of the system's memory
to gigantic hugepages for VM memory.

If this memory needs to come from scratch space, then scratch needs to
be greater than the memory needed for huge pages, which is impractical.
In addition, hugepages can be preserved memory. Allocating them from
scratch violates the assumption that scratch contains no preserved
memory.

Methodology
===========

Introduce extended scratch areas. These areas are discovered at boot by
walking the preserved memory radix tree and looking for free blocks of
memory. They then marked as scratch to allow allocations from them. This
makes KHO more resilient to memory pressure and allows supporting huge
page preservation.

Since the preserved memory radix tree mixes both physical address and
order into a single key, and does not track table pages, it is difficult
to identify free areas from it directly. Walk the tree and digest it
down into another radix tree. The latter tracks blocks of
KHO_EXT_SHIFT (1 GiB as of now) granularity. Then walk the digested tree
and mark the areas between the present keys as scratch.

Performance
===========

The discovery algorithm traverses the preserved memory radix tree
exactly once. While it does use memory for the digested radix tree,
since the blocks are split by 1 GiB, a single bitmap with 4k pages can
track up to 32 TiB of memory. So there are likely to be very few radix
tree pages used in this tracking. For systems with all physical memory
below 32 TiB, this should result in a total of 6 pages being
used (KHO_TREE_MAX_DEPTH == 6).

An alternate way of achieving this would be to call kho_mem_retrieve()
earlier in boot and mark all the KHO preservations as reserved. But that
can blow up memblock.reserved with a bunch of 4K pages scattered
everywhere, which will reduce performance of subsequent allocations.
Since the free blocks are tracked in chunks of 1 GiB, this won't blow up
memblock.memory as much.

Practical evaluation
====================

The testing is done on a x86_64 qemu VM running under KVM with 64G
memory and 12 CPUs. The machine pre-allocates 50 1G pages.

Since the performance scales with how busy the radix tree is, tests are
done with 2 preservation patterns: first with two 1M memfds, second with
two 1G memfds, both using 4k pages.

Test case 1 - 1M memfd
~~~~~~~~~~~~~~~~~~~~~~

This test case has two memfds with 1M memory each in 4k pages, plus
other preservations from LUO core and other KHO users.

This is how the radix tree stats look like:

    radix_nodes:       0x2f
    nr_preservations:  0x22d
    mem_preserved:     0xa2b000

    per order preservations:
    order  0:  0x215
    order  1:  0x9
    order  2:  0x1
    order  3:  0x2
    order  4:  0x5
    order  5:  0x1
    order  6:  0x2
    order  7:  0x2
    order  9:  0x1
    order 10:  0x1

and this is how long it takes to extend the scratch after KHO boot:

    kho_extend_scratch(): time taken: 88 us
    kho_extend_scratch(): total memory recovered: 0xf7ff7b000 (~62G)

Test case 2 - 1G memfd
~~~~~~~~~~~~~~~~~~~~~~

This test case has two memfds with 1G memory each in 4k pages, plus
other preservations from LUO core and other KHO users.

This is how the radix tree stats look like:

    radix_nodes:       0x45
    nr_preservations:  0x80832
    mem_preserved:     0x8102d000

    per order preservations:
    order  0:  0x80817
    order  1:  0x7
    order  2:  0x2
    order  3:  0x4
    order  4:  0x2
    order  5:  0x2
    order  6:  0x4
    order  7:  0x3
    order  8:  0x1
    order  9:  0x2

and this is how long it takes to extend the scratch after KHO boot:

    kho_extend_scratch(): time taken: 21769 us
    kho_extend_scratch(): total memory recovered: 0xe40000000 (57G)

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 include/linux/kexec_handover.h     |   1 +
 kernel/liveupdate/kexec_handover.c | 148 +++++++++++++++++++++++++----
 mm/mm_init.c                       |   1 +
 3 files changed, 133 insertions(+), 17 deletions(-)

diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
index 8968c56d2d73..6ce46f36ed99 100644
--- a/include/linux/kexec_handover.h
+++ b/include/linux/kexec_handover.h
@@ -37,6 +37,7 @@ void kho_remove_subtree(void *blob);
 int kho_retrieve_subtree(const char *name, phys_addr_t *phys, size_t *size);
 
 void kho_memory_init(void);
+void kho_extend_scratch(void);
 
 void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys,
 		  u64 scratch_len);
diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 1a04e089f779..c2b843a5fb28 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -84,6 +84,23 @@ static struct kho_out kho_out = {
 	},
 };
 
+struct kho_in {
+	phys_addr_t fdt_phys;
+	phys_addr_t scratch_phys;
+	char previous_release[__NEW_UTS_LEN + 1];
+	u32 kexec_count;
+	struct kho_debugfs dbg;
+	struct kho_radix_tree radix_tree;
+};
+
+static struct kho_in kho_in = {
+};
+
+static const void *kho_get_fdt(void)
+{
+	return kho_in.fdt_phys ? phys_to_virt(kho_in.fdt_phys) : NULL;
+}
+
 /**
  * kho_encode_radix_key - Encodes a physical address and order into a radix key.
  * @phys: The physical address of the page.
@@ -840,6 +857,120 @@ static void __init kho_reserve_scratch(void)
 	kho_enable = false;
 }
 
+#define KHO_EXT_SHIFT 30 /* 1 GiB */
+
+static int __init kho_ext_walk_key(unsigned long key, void *data)
+{
+	struct kho_radix_tree *tree = data;
+	phys_addr_t start, end;
+	unsigned int order;
+	int err;
+
+	start = kho_decode_radix_key(key, &order);
+	end = start + (1UL << (order + PAGE_SHIFT));
+
+	while (start < end) {
+		err = kho_radix_add_key(tree, start >> KHO_EXT_SHIFT);
+		if (err)
+			return err;
+
+		start += (1UL << KHO_EXT_SHIFT);
+	}
+
+	return 0;
+}
+
+static int __init kho_ext_walk_table(phys_addr_t phys, void *data)
+{
+	struct kho_radix_tree *tree = data;
+
+	return kho_radix_add_key(tree, phys >> KHO_EXT_SHIFT);
+}
+
+static int __init kho_ext_mark_scratch(unsigned long key, void *data)
+{
+	phys_addr_t *prev_end = data;
+	phys_addr_t start = key << KHO_EXT_SHIFT;
+	int err;
+
+	if (start > *prev_end) {
+		err = memblock_mark_kho_scratch_ext(*prev_end, start - *prev_end);
+		if (err)
+			return err;
+	}
+
+	*prev_end = start + (1UL << KHO_EXT_SHIFT);
+	return 0;
+}
+
+/**
+ * kho_extend_scratch - Extend the scratch regions
+ *
+ * The KHO radix tree mixes both physical address and order into a single key.
+ * This makes it hard to look for free ranges directly. This function first
+ * walks the radix tree and digests it down into another radix tree, whose keys
+ * identify blocks of KHO_EXT_SHIFT which contain preserved memory.
+ *
+ * Then it walks the digested radix tree and marks everything that doesn't have
+ * preserved memory as scratch.
+ *
+ * NOTE: This function allocates memory so it should be called when scratch has
+ * available space.
+ *
+ * NOTE: The pages of the KHO radix tree tables are not marked as preserved in
+ * the KHO tree. But they are expected to remain untouched until the tree is
+ * fully parsed. So this function also considers them to be "preserved memory"
+ * and marks their blocks as busy.
+ */
+void __init kho_extend_scratch(void)
+{
+	const struct kho_radix_walk_cb kho_cb = {
+		.key = kho_ext_walk_key,
+		.table = kho_ext_walk_table,
+	};
+	const struct kho_radix_walk_cb ext_cb = {
+		.key = kho_ext_mark_scratch,
+	};
+	struct kho_radix_tree radix;
+	phys_addr_t prev_end = 0, mem_map_phys;
+	int err = 0;
+
+	if (!is_kho_boot())
+		return;
+
+	/* Make sure the KHO radix tree is initialized. */
+	mem_map_phys = kho_get_mem_map_phys(kho_get_fdt());
+	err = kho_radix_init_tree(&kho_in.radix_tree, phys_to_virt(mem_map_phys));
+	if (err)
+		goto print;
+
+	err = kho_radix_init_tree(&radix, NULL);
+	if (err)
+		goto print;
+
+	/* Walk the KHO radix tree to find busy blocks. */
+	err = kho_radix_walk_tree(&kho_in.radix_tree, &kho_cb, &radix);
+	if (err)
+		goto out;
+
+	/* Walk the blocks and mark everything between keys as scratch. */
+	err = kho_radix_walk_tree(&radix, &ext_cb, &prev_end);
+	if (err)
+		goto out;
+
+	/* Mark everything from last busy block to end of DRAM. */
+	if (prev_end < memblock_end_of_DRAM())
+		err = memblock_mark_kho_scratch_ext(prev_end,
+						    memblock_end_of_DRAM() - prev_end);
+
+	/* fallthrough */
+out:
+	kho_radix_destroy_tree(&radix);
+print:
+	if (err)
+		pr_err("Failed to extend scratch: %pe\n", ERR_PTR(err));
+}
+
 /**
  * kho_add_subtree - record the physical address of a sub blob in KHO root tree.
  * @name: name of the sub tree.
@@ -1384,23 +1515,6 @@ void kho_restore_free(void *mem)
 }
 EXPORT_SYMBOL_GPL(kho_restore_free);
 
-struct kho_in {
-	phys_addr_t fdt_phys;
-	phys_addr_t scratch_phys;
-	char previous_release[__NEW_UTS_LEN + 1];
-	u32 kexec_count;
-	struct kho_debugfs dbg;
-	struct kho_radix_tree radix_tree;
-};
-
-static struct kho_in kho_in = {
-};
-
-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
diff --git a/mm/mm_init.c b/mm/mm_init.c
index eddc0f03a779..10916cdf0029 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -2688,6 +2688,7 @@ void __init __weak mem_init(void)
 
 void __init mm_core_init_early(void)
 {
+	kho_extend_scratch();
 	hugetlb_cma_reserve();
 	hugetlb_bootmem_alloc();
 
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 11/12] kho: return virtual address of mem_map

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

There are currently 3 callers of kho_get_mem_map_phys(). Two of them,
kho_mem_retrieve() and kho_extend_scratch() need the virtual address.
The third, kho_populate() doesn't care. Make things simpler by
directly returning the virtual address. Rename kho_get_mem_map_phys() to
kho_get_mem_map() to accurately reflect what it returns.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 28 +++++++++++++++-------------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index c2b843a5fb28..2e13b80d1c7d 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -625,10 +625,11 @@ static int __init kho_preserved_memory_reserve(unsigned long key, void *data)
 	return 0;
 }
 
-/* Returns physical address of the preserved memory map from FDT */
-static phys_addr_t __init kho_get_mem_map_phys(const void *fdt)
+/* Returns virtual address of the preserved memory map from FDT */
+static __init void *kho_get_mem_map(const void *fdt)
 {
 	const void *mem_ptr;
+	phys_addr_t mem_map_phys;
 	int len;
 
 	mem_ptr = fdt_getprop(fdt, 0, KHO_FDT_MEMORY_MAP_PROP_NAME, &len);
@@ -637,7 +638,11 @@ static phys_addr_t __init kho_get_mem_map_phys(const void *fdt)
 		return 0;
 	}
 
-	return get_unaligned((const u64 *)mem_ptr);
+	mem_map_phys = get_unaligned((const u64 *)mem_ptr);
+	if (!mem_map_phys)
+		return NULL;
+
+	return phys_to_virt(mem_map_phys);
 }
 
 /*
@@ -932,15 +937,15 @@ void __init kho_extend_scratch(void)
 		.key = kho_ext_mark_scratch,
 	};
 	struct kho_radix_tree radix;
-	phys_addr_t prev_end = 0, mem_map_phys;
+	phys_addr_t prev_end = 0;
 	int err = 0;
 
 	if (!is_kho_boot())
 		return;
 
 	/* Make sure the KHO radix tree is initialized. */
-	mem_map_phys = kho_get_mem_map_phys(kho_get_fdt());
-	err = kho_radix_init_tree(&kho_in.radix_tree, phys_to_virt(mem_map_phys));
+	err = kho_radix_init_tree(&kho_in.radix_tree,
+				  kho_get_mem_map(kho_get_fdt()));
 	if (err)
 		goto print;
 
@@ -1587,11 +1592,9 @@ static int __init kho_mem_retrieve(const void *fdt)
 	const struct kho_radix_walk_cb cb = {
 		.key = kho_preserved_memory_reserve,
 	};
-	phys_addr_t mem_map_phys;
 	int err;
 
-	mem_map_phys = kho_get_mem_map_phys(fdt);
-	err = kho_radix_init_tree(&kho_in.radix_tree, phys_to_virt(mem_map_phys));
+	err = kho_radix_init_tree(&kho_in.radix_tree, kho_get_mem_map(fdt));
 	if (err)
 		return err;
 
@@ -1816,8 +1819,7 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 {
 	unsigned int scratch_cnt = scratch_len / sizeof(*kho_scratch);
 	struct kho_scratch *scratch = NULL;
-	phys_addr_t mem_map_phys;
-	void *fdt = NULL;
+	void *fdt = NULL, *mem_map;
 	bool populated = false;
 	int err;
 
@@ -1840,8 +1842,8 @@ void __init kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
 		goto unmap_fdt;
 	}
 
-	mem_map_phys = kho_get_mem_map_phys(fdt);
-	if (!mem_map_phys)
+	mem_map = kho_get_mem_map(fdt);
+	if (!mem_map)
 		goto unmap_fdt;
 
 	scratch = early_memremap(scratch_phys, scratch_len);
-- 
2.54.0.545.g6539524ca2-goog

[PATCH 12/12] mm/hugetlb: make bootmem allocation work with KHO

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

Gigantic page allocation is somewhat broken currently when KHO is used.

Firstly, they break KHO scratch size accounting. RSRV_KERN is used to
track how much memory is reserved for use by the kernel. Since
alloc_bootmem() calls the memblock_alloc*() APIs, the hugepages
allocated also get marked as RSRV_KERN.

Allocations marked RSRV_KERN are used by KHO to calculate how much
scratch space it should reserve to make sure the next kernel has enough
memory to boot when it is in scratch-only phase. Counting hugepages in
that blows up scratch size, and can lead to the scratch allocation
failing, making KHO unusable. This will show up when huge pages make up
more than 50% of the system, which is a fairly common use case.

Secondly, while not supported right now, huge pages are user memory and
can be preserved via KHO. The scratch spaces should not have any
preserved memory. Allocating hugepages from scratch (on a KHO boot) can
lead to them being un-preservable.

Introduce memblock_alloc_nid_user(). This does two things: first, it
instructs __memblock_alloc_range_nid() to not use scratch areas to
fulfill allocation. If KHO is in scratch-only mode, allocations will
only be made from extended scratch areas. Second, it removes RSRV_KERN
from the allocation to make sure it doesn't mess up scratch size
accounting.

To reduce duplication, introduce __memblock_alloc_range_nid() which does
exactly what memblock_alloc_range_nid() used to do, but takes the flags
from its caller. Then make memblock_alloc_range_nid() a wrapper to it.
This lets memblock_alloc_nid_user() re-use most of the logic without
causing churn to update all callers of memblock_alloc_range_nid() and
adding yet another argument to it.

Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
---

Notes:
    Checkpatch complains here about the alignment of arguments of
    memblock_alloc_range_nid() with open parentheses. That can be ignored
    since the code already was mis-aligned, and for good reason.

 include/linux/memblock.h |   4 ++
 mm/hugetlb.c             |  19 ++----
 mm/memblock.c            | 138 ++++++++++++++++++++++++++++++---------
 3 files changed, 116 insertions(+), 45 deletions(-)

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index 4f535ca4947a..c7056cf3f0f2 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -160,6 +160,7 @@ int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
 int memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t size);
 int memblock_reserved_mark_kern(phys_addr_t base, phys_addr_t size);
+int memblock_reserved_clear_kern(phys_addr_t base, phys_addr_t size);
 int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size);
 int memblock_mark_kho_scratch_ext(phys_addr_t base, phys_addr_t size);
 int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size);
@@ -431,6 +432,9 @@ void *memblock_alloc_try_nid(phys_addr_t size, phys_addr_t align,
 			     phys_addr_t min_addr, phys_addr_t max_addr,
 			     int nid);
 
+void *memblock_alloc_nid_user(phys_addr_t size, phys_addr_t align, int nid,
+			      bool exact_nid);
+
 static __always_inline void *memblock_alloc(phys_addr_t size, phys_addr_t align)
 {
 	return memblock_alloc_try_nid(size, align, MEMBLOCK_LOW_LIMIT,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f24bf49be047..5ba393b0a581 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3049,26 +3049,19 @@ static __init void *alloc_bootmem(struct hstate *h, int nid, bool node_exact)
 	if (hugetlb_early_cma(h))
 		m = hugetlb_cma_alloc_bootmem(h, &listnode, node_exact);
 	else {
-		if (node_exact)
-			m = memblock_alloc_exact_nid_raw(huge_page_size(h),
-				huge_page_size(h), 0,
-				MEMBLOCK_ALLOC_ACCESSIBLE, nid);
-		else {
-			m = memblock_alloc_try_nid_raw(huge_page_size(h),
-				huge_page_size(h), 0,
-				MEMBLOCK_ALLOC_ACCESSIBLE, nid);
+		m = memblock_alloc_nid_user(huge_page_size(h), huge_page_size(h),
+					    nid, node_exact);
+		if (m) {
 			/*
 			 * For pre-HVO to work correctly, pages need to be on
 			 * the list for the node they were actually allocated
 			 * from. That node may be different in the case of
-			 * fallback by memblock_alloc_try_nid_raw. So,
-			 * extract the actual node first.
+			 * fallback by memblock_alloc_try_nid_raw. So, extract
+			 * the actual node first.
 			 */
-			if (m)
+			if (node_exact)
 				listnode = early_pfn_to_nid(PHYS_PFN(__pa(m)));
-		}
 
-		if (m) {
 			m->flags = 0;
 			m->cma = NULL;
 		}
diff --git a/mm/memblock.c b/mm/memblock.c
index 79443e004361..504b5b0c8af7 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -178,11 +178,21 @@ bool __init_memblock memblock_has_mirror(void)
 	return system_has_some_mirror;
 }
 
-static enum memblock_flags __init_memblock choose_memblock_flags(void)
+static enum memblock_flags __init_memblock choose_memblock_flags(bool user)
 {
 	/* skip non-scratch memory for kho early boot allocations */
-	if (kho_scratch_only)
-		return MEMBLOCK_KHO_SCRATCH | MEMBLOCK_KHO_SCRATCH_EXT;
+	if (kho_scratch_only) {
+		enum memblock_flags flags = MEMBLOCK_KHO_SCRATCH_EXT;
+
+		/*
+		 * Scratch can only be used for kernel memory, since user memory
+		 * might be preserved and thus can not be in scratch.
+		 */
+		if (!user)
+			flags |= MEMBLOCK_KHO_SCRATCH;
+
+		return flags;
+	}
 
 	return system_has_some_mirror ? MEMBLOCK_MIRROR : MEMBLOCK_NONE;
 }
@@ -346,7 +356,7 @@ static phys_addr_t __init_memblock memblock_find_in_range(phys_addr_t start,
 					phys_addr_t align)
 {
 	phys_addr_t ret;
-	enum memblock_flags flags = choose_memblock_flags();
+	enum memblock_flags flags = choose_memblock_flags(false);
 
 again:
 	ret = memblock_find_in_range_node(size, align, start, end,
@@ -1173,6 +1183,20 @@ int __init_memblock memblock_reserved_mark_kern(phys_addr_t base, phys_addr_t si
 				    MEMBLOCK_RSRV_KERN);
 }
 
+/**
+ * memblock_reserved_clear_kern - Clear MEMBLOCK_RSRV_KERN flag for region
+ *
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+int __init_memblock memblock_reserved_clear_kern(phys_addr_t base, phys_addr_t size)
+{
+	return memblock_setclr_flag(&memblock.reserved, base, size, 0,
+				    MEMBLOCK_RSRV_KERN);
+}
+
 /**
  * memblock_mark_kho_scratch - Mark a memory region as MEMBLOCK_KHO_SCRATCH.
  * @base: the base phys addr of the region
@@ -1532,37 +1556,11 @@ int __init_memblock memblock_set_node(phys_addr_t base, phys_addr_t size,
 	return 0;
 }
 
-/**
- * memblock_alloc_range_nid - allocate boot memory block
- * @size: size of memory block to be allocated in bytes
- * @align: alignment of the region and block's size
- * @start: the lower bound of the memory region to allocate (phys address)
- * @end: the upper bound of the memory region to allocate (phys address)
- * @nid: nid of the free area to find, %NUMA_NO_NODE for any node
- * @exact_nid: control the allocation fall back to other nodes
- *
- * The allocation is performed from memory region limited by
- * memblock.current_limit if @end == %MEMBLOCK_ALLOC_ACCESSIBLE.
- *
- * If the specified node can not hold the requested memory and @exact_nid
- * is false, the allocation falls back to any node in the system.
- *
- * For systems with memory mirroring, the allocation is attempted first
- * from the regions with mirroring enabled and then retried from any
- * memory region.
- *
- * In addition, function using kmemleak_alloc_phys for allocated boot
- * memory block, it is never reported as leaks.
- *
- * Return:
- * Physical address of allocated memory block on success, %0 on failure.
- */
-phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
+static phys_addr_t __init __memblock_alloc_range_nid(phys_addr_t size,
 					phys_addr_t align, phys_addr_t start,
 					phys_addr_t end, int nid,
-					bool exact_nid)
+					bool exact_nid, enum memblock_flags flags)
 {
-	enum memblock_flags flags = choose_memblock_flags();
 	phys_addr_t found;
 
 	/*
@@ -1631,6 +1629,41 @@ phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
 	return found;
 }
 
+/**
+ * memblock_alloc_range_nid - allocate boot memory block
+ * @size: size of memory block to be allocated in bytes
+ * @align: alignment of the region and block's size
+ * @start: the lower bound of the memory region to allocate (phys address)
+ * @end: the upper bound of the memory region to allocate (phys address)
+ * @nid: nid of the free area to find, %NUMA_NO_NODE for any node
+ * @exact_nid: control the allocation fall back to other nodes
+ *
+ * The allocation is performed from memory region limited by
+ * memblock.current_limit if @end == %MEMBLOCK_ALLOC_ACCESSIBLE.
+ *
+ * If the specified node can not hold the requested memory and @exact_nid
+ * is false, the allocation falls back to any node in the system.
+ *
+ * For systems with memory mirroring, the allocation is attempted first
+ * from the regions with mirroring enabled and then retried from any
+ * memory region.
+ *
+ * In addition, function using kmemleak_alloc_phys for allocated boot
+ * memory block, it is never reported as leaks.
+ *
+ * Return:
+ * Physical address of allocated memory block on success, %0 on failure.
+ */
+phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
+					phys_addr_t align, phys_addr_t start,
+					phys_addr_t end, int nid,
+					bool exact_nid)
+{
+	enum memblock_flags flags = choose_memblock_flags(false);
+
+	return __memblock_alloc_range_nid(size, align, start, end, nid, exact_nid, flags);
+}
+
 /**
  * memblock_phys_alloc_range - allocate a memory block inside specified range
  * @size: size of memory block to be allocated in bytes
@@ -1782,6 +1815,47 @@ void * __init memblock_alloc_try_nid_raw(
 				       false);
 }
 
+/**
+ * memblock_alloc_nid_user - allocate boot memory for use by userspace
+ * @size: size of the memory block to be allocated in bytes
+ * @align: alignment of the region and block's size
+ * @exact_nid: control the allocation fall back to other nodes
+ *
+ * Public function, provides additional debug information (including caller
+ * info), if enabled. Does not zero allocated memory, does not panic if request
+ * cannot be satisfied.
+ *
+ * If the specified node can not hold the requested memory and @exact_nid is
+ * false, the allocation falls back to any node in the system. The allocated
+ * memory has no restrictions on minimum or maximum address, and does not count
+ * towards %MEMBLOCK_RSRV_KERN.
+ *
+ * Return:
+ * Virtual address of allocated memory block on success, %NULL on failure.
+ */
+void * __init memblock_alloc_nid_user(phys_addr_t size, phys_addr_t align,
+				      int nid, bool exact_nid)
+{
+	enum memblock_flags flags = choose_memblock_flags(true);
+	phys_addr_t alloc;
+
+	memblock_dbg("%s: %llu bytes align=0x%llx nid=%d %pS\n",
+		     __func__, (u64)size, (u64)align, nid, (void *)_RET_IP_);
+
+	alloc = __memblock_alloc_range_nid(size, align, 0, MEMBLOCK_ALLOC_ACCESSIBLE,
+					   nid, exact_nid, flags);
+	if (!alloc)
+		return NULL;
+
+	/* User memory should not be marked with RSRV_KERN. */
+	if (memblock_reserved_clear_kern(alloc, size)) {
+		memblock_phys_free(alloc, size);
+		return NULL;
+	}
+
+	return phys_to_virt(alloc);
+}
+
 /**
  * memblock_alloc_try_nid - allocate boot memory block
  * @size: size of memory block to be allocated in bytes
-- 
2.54.0.545.g6539524ca2-goog