[RFC PATCH v1 14/57] pm/hibernate: Remove PAGE_SIZE compile-time constant assumption

[Ryan Roberts <ryan.roberts@arm.com>]

To prepare for supporting boot-time page size selection, refactor code
to remove assumptions about PAGE_SIZE being compile-time constant. Code
intended to be equivalent when compile-time page size is active.

"struct linked_page", "struct swap_map_page" and "struct swsusp_header"
were all previously sized to be exactly PAGE_SIZE. Refactor those
structures to remove the padding, then superimpose them on a page at
runtime.

"struct cmp_data" and "struct dec_data" previously contained embedded
"unc" and "cmp" arrays, who's sizes were derived from PAGE_SIZE. We
can't use flexible array approach here since there are 2 arrays in the
structure, so convert to pointers and define an allocator and
deallocator for each struct.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---

***NOTE***
Any confused maintainers may want to read the cover note here for context:
https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/

 kernel/power/power.h    |   2 +-
 kernel/power/snapshot.c |   2 +-
 kernel/power/swap.c     | 129 +++++++++++++++++++++++++++++++++-------
 3 files changed, 108 insertions(+), 25 deletions(-)

diff --git a/kernel/power/power.h b/kernel/power/power.h
index de0e6b1077f23..74af2eb8d48a4 100644
--- a/kernel/power/power.h
+++ b/kernel/power/power.h
@@ -16,7 +16,7 @@ struct swsusp_info {
 	unsigned long		image_pages;
 	unsigned long		pages;
 	unsigned long		size;
-} __aligned(PAGE_SIZE);
+} __aligned(PAGE_SIZE_MAX);
 
 #ifdef CONFIG_HIBERNATION
 /* kernel/power/snapshot.c */
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 405eddbda4fc5..144e92f786e35 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -155,7 +155,7 @@ struct pbe *restore_pblist;
 
 struct linked_page {
 	struct linked_page *next;
-	char data[LINKED_PAGE_DATA_SIZE];
+	char data[];
 } __packed;
 
 /*
diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index 82b884b67152f..ffd4c864acfa2 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -59,6 +59,7 @@ static bool clean_pages_on_decompress;
  */
 
 #define MAP_PAGE_ENTRIES	(PAGE_SIZE / sizeof(sector_t) - 1)
+#define NEXT_SWAP_INDEX		MAP_PAGE_ENTRIES
 
 /*
  * Number of free pages that are not high.
@@ -78,8 +79,11 @@ static inline unsigned long reqd_free_pages(void)
 }
 
 struct swap_map_page {
-	sector_t entries[MAP_PAGE_ENTRIES];
-	sector_t next_swap;
+	/*
+	 * A PAGE_SIZE structure with (PAGE_SIZE / sizeof(sector_t)) entries.
+	 * The last entry, [NEXT_SWAP_INDEX], is `.next_swap`.
+	 */
+	sector_t entries[1];
 };
 
 struct swap_map_page_list {
@@ -103,8 +107,6 @@ struct swap_map_handle {
 };
 
 struct swsusp_header {
-	char reserved[PAGE_SIZE - 20 - sizeof(sector_t) - sizeof(int) -
-	              sizeof(u32) - sizeof(u32)];
 	u32	hw_sig;
 	u32	crc32;
 	sector_t image;
@@ -113,6 +115,7 @@ struct swsusp_header {
 	char	sig[10];
 } __packed;
 
+static char *swsusp_header_pg;
 static struct swsusp_header *swsusp_header;
 
 /*
@@ -315,7 +318,7 @@ static int mark_swapfiles(struct swap_map_handle *handle, unsigned int flags)
 {
 	int error;
 
-	hib_submit_io(REQ_OP_READ, swsusp_resume_block, swsusp_header, NULL);
+	hib_submit_io(REQ_OP_READ, swsusp_resume_block, swsusp_header_pg, NULL);
 	if (!memcmp("SWAP-SPACE",swsusp_header->sig, 10) ||
 	    !memcmp("SWAPSPACE2",swsusp_header->sig, 10)) {
 		memcpy(swsusp_header->orig_sig,swsusp_header->sig, 10);
@@ -329,7 +332,7 @@ static int mark_swapfiles(struct swap_map_handle *handle, unsigned int flags)
 		if (flags & SF_CRC32_MODE)
 			swsusp_header->crc32 = handle->crc32;
 		error = hib_submit_io(REQ_OP_WRITE | REQ_SYNC,
-				      swsusp_resume_block, swsusp_header, NULL);
+				      swsusp_resume_block, swsusp_header_pg, NULL);
 	} else {
 		pr_err("Swap header not found!\n");
 		error = -ENODEV;
@@ -466,7 +469,7 @@ static int swap_write_page(struct swap_map_handle *handle, void *buf,
 		offset = alloc_swapdev_block(root_swap);
 		if (!offset)
 			return -ENOSPC;
-		handle->cur->next_swap = offset;
+		handle->cur->entries[NEXT_SWAP_INDEX] = offset;
 		error = write_page(handle->cur, handle->cur_swap, hb);
 		if (error)
 			goto out;
@@ -643,8 +646,8 @@ struct cmp_data {
 	wait_queue_head_t done;                   /* compression done */
 	size_t unc_len;                           /* uncompressed length */
 	size_t cmp_len;                           /* compressed length */
-	unsigned char unc[UNC_SIZE];              /* uncompressed buffer */
-	unsigned char cmp[CMP_SIZE];              /* compressed buffer */
+	unsigned char *unc;                       /* uncompressed buffer */
+	unsigned char *cmp;                       /* compressed buffer */
 };
 
 /* Indicates the image size after compression */
@@ -683,6 +686,45 @@ static int compress_threadfn(void *data)
 	return 0;
 }
 
+static void free_cmp_data(struct cmp_data *data, unsigned nr_threads)
+{
+	int i;
+
+	if (!data)
+		return;
+
+	for (i = 0; i < nr_threads; i++) {
+		vfree(data[i].unc);
+		vfree(data[i].cmp);
+	}
+
+	vfree(data);
+}
+
+static struct cmp_data *alloc_cmp_data(unsigned nr_threads)
+{
+	struct cmp_data *data = NULL;
+	int i = -1;
+
+	data = vzalloc(array_size(nr_threads, sizeof(*data)));
+	if (!data)
+		goto fail;
+
+	for (i = 0; i < nr_threads; i++) {
+		data[i].unc = vzalloc(UNC_SIZE);
+		if (!data[i].unc)
+			goto fail;
+		data[i].cmp = vzalloc(CMP_SIZE);
+		if (!data[i].cmp)
+			goto fail;
+	}
+
+	return data;
+fail:
+	free_cmp_data(data, nr_threads);
+	return NULL;
+}
+
 /**
  * save_compressed_image - Save the suspend image data after compression.
  * @handle: Swap map handle to use for saving the image.
@@ -724,7 +766,7 @@ static int save_compressed_image(struct swap_map_handle *handle,
 		goto out_clean;
 	}
 
-	data = vzalloc(array_size(nr_threads, sizeof(*data)));
+	data = alloc_cmp_data(nr_threads);
 	if (!data) {
 		pr_err("Failed to allocate %s data\n", hib_comp_algo);
 		ret = -ENOMEM;
@@ -902,7 +944,7 @@ static int save_compressed_image(struct swap_map_handle *handle,
 			if (data[thr].cc)
 				crypto_free_comp(data[thr].cc);
 		}
-		vfree(data);
+		free_cmp_data(data, nr_threads);
 	}
 	if (page) free_page((unsigned long)page);
 
@@ -1036,7 +1078,7 @@ static int get_swap_reader(struct swap_map_handle *handle,
 			release_swap_reader(handle);
 			return error;
 		}
-		offset = tmp->map->next_swap;
+		offset = tmp->map->entries[NEXT_SWAP_INDEX];
 	}
 	handle->k = 0;
 	handle->cur = handle->maps->map;
@@ -1150,8 +1192,8 @@ struct dec_data {
 	wait_queue_head_t done;                   /* decompression done */
 	size_t unc_len;                           /* uncompressed length */
 	size_t cmp_len;                           /* compressed length */
-	unsigned char unc[UNC_SIZE];              /* uncompressed buffer */
-	unsigned char cmp[CMP_SIZE];              /* compressed buffer */
+	unsigned char *unc;                       /* uncompressed buffer */
+	unsigned char *cmp;                       /* compressed buffer */
 };
 
 /*
@@ -1189,6 +1231,45 @@ static int decompress_threadfn(void *data)
 	return 0;
 }
 
+static void free_dec_data(struct dec_data *data, unsigned nr_threads)
+{
+	int i;
+
+	if (!data)
+		return;
+
+	for (i = 0; i < nr_threads; i++) {
+		vfree(data[i].unc);
+		vfree(data[i].cmp);
+	}
+
+	vfree(data);
+}
+
+static struct dec_data *alloc_dec_data(unsigned nr_threads)
+{
+	struct dec_data *data = NULL;
+	int i = -1;
+
+	data = vzalloc(array_size(nr_threads, sizeof(*data)));
+	if (!data)
+		goto fail;
+
+	for (i = 0; i < nr_threads; i++) {
+		data[i].unc = vzalloc(UNC_SIZE);
+		if (!data[i].unc)
+			goto fail;
+		data[i].cmp = vzalloc(CMP_SIZE);
+		if (!data[i].cmp)
+			goto fail;
+	}
+
+	return data;
+fail:
+	free_dec_data(data, nr_threads);
+	return NULL;
+}
+
 /**
  * load_compressed_image - Load compressed image data and decompress it.
  * @handle: Swap map handle to use for loading data.
@@ -1231,7 +1312,7 @@ static int load_compressed_image(struct swap_map_handle *handle,
 		goto out_clean;
 	}
 
-	data = vzalloc(array_size(nr_threads, sizeof(*data)));
+	data = alloc_dec_data(nr_threads);
 	if (!data) {
 		pr_err("Failed to allocate %s data\n", hib_comp_algo);
 		ret = -ENOMEM;
@@ -1510,7 +1591,7 @@ static int load_compressed_image(struct swap_map_handle *handle,
 			if (data[thr].cc)
 				crypto_free_comp(data[thr].cc);
 		}
-		vfree(data);
+		free_dec_data(data, nr_threads);
 	}
 	vfree(page);
 
@@ -1569,9 +1650,9 @@ int swsusp_check(bool exclusive)
 	hib_resume_bdev_file = bdev_file_open_by_dev(swsusp_resume_device,
 				BLK_OPEN_READ, holder, NULL);
 	if (!IS_ERR(hib_resume_bdev_file)) {
-		clear_page(swsusp_header);
+		clear_page(swsusp_header_pg);
 		error = hib_submit_io(REQ_OP_READ, swsusp_resume_block,
-					swsusp_header, NULL);
+					swsusp_header_pg, NULL);
 		if (error)
 			goto put;
 
@@ -1581,7 +1662,7 @@ int swsusp_check(bool exclusive)
 			/* Reset swap signature now */
 			error = hib_submit_io(REQ_OP_WRITE | REQ_SYNC,
 						swsusp_resume_block,
-						swsusp_header, NULL);
+						swsusp_header_pg, NULL);
 		} else {
 			error = -EINVAL;
 		}
@@ -1631,12 +1712,12 @@ int swsusp_unmark(void)
 	int error;
 
 	hib_submit_io(REQ_OP_READ, swsusp_resume_block,
-			swsusp_header, NULL);
+			swsusp_header_pg, NULL);
 	if (!memcmp(HIBERNATE_SIG,swsusp_header->sig, 10)) {
 		memcpy(swsusp_header->sig,swsusp_header->orig_sig, 10);
 		error = hib_submit_io(REQ_OP_WRITE | REQ_SYNC,
 					swsusp_resume_block,
-					swsusp_header, NULL);
+					swsusp_header_pg, NULL);
 	} else {
 		pr_err("Cannot find swsusp signature!\n");
 		error = -ENODEV;
@@ -1653,9 +1734,11 @@ int swsusp_unmark(void)
 
 static int __init swsusp_header_init(void)
 {
-	swsusp_header = (struct swsusp_header*) __get_free_page(GFP_KERNEL);
-	if (!swsusp_header)
+	swsusp_header_pg = (char *)__get_free_page(GFP_KERNEL);
+	if (!swsusp_header_pg)
 		panic("Could not allocate memory for swsusp_header\n");
+	swsusp_header = (struct swsusp_header *)(swsusp_header_pg +
+				PAGE_SIZE - sizeof(struct swsusp_header));
 	return 0;
 }
 
-- 
2.43.0