[POWERPC] pseries: Force 4k update_flash block and list sizes

The enablement of 64k pages on pseries platforms exposed a bug in
the RTAS mechanism for updating firmware. RTAS assumes 4k for flash
block and list sizes, and use of any other sizes results in a failure,
even though PAPR does not specify any such requirement.

This patch changes the rtas_flash module to force the use of 4k memory
block and list sizes when preparing and sending a firmware image to
RTAS. The rtas_flash function now uses a slab cache of 4k blocks with
4k alignment, rather than get_zeroed_page(), to allocate the memory for
the flash blocks and lists. The 4k alignment requirement is specified
in PAPR.

Signed-off-by: John Rose <[e-mail]>
Signed-off-by: Paul Mackerras <[e-mail]>

arch/powerpc/kernel/rtas_flash.c

···
 #define VALIDATE_BUF_SIZE 4096    
 #define RTAS_MSG_MAXLEN   64
 
+/* Quirk - RTAS requires 4k list length and block size */
+#define RTAS_BLKLIST_LENGTH 4096
+#define RTAS_BLK_SIZE 4096
+
 struct flash_block {
 	char *data;
 	unsigned long length;
···
  * into a version/length and translate the pointers
  * to absolute.
  */
-#define FLASH_BLOCKS_PER_NODE ((PAGE_SIZE - 16) / sizeof(struct flash_block))
+#define FLASH_BLOCKS_PER_NODE ((RTAS_BLKLIST_LENGTH - 16) / sizeof(struct flash_block))
 struct flash_block_list {
 	unsigned long num_blocks;
 	struct flash_block_list *next;
···
 };
 
 static struct flash_block_list_header rtas_firmware_flash_list = {0, NULL};
+
+/* Use slab cache to guarantee 4k alignment */
+static kmem_cache_t *flash_block_cache = NULL;
 
 #define FLASH_BLOCK_LIST_VERSION (1UL)
 
···
 				return FLASH_IMG_NULL_DATA;
 			}
 			block_size = f->blocks[i].length;
-			if (block_size <= 0 || block_size > PAGE_SIZE) {
+			if (block_size <= 0 || block_size > RTAS_BLK_SIZE) {
 				return FLASH_IMG_BAD_LEN;
 			}
 			image_size += block_size;
···
 
 	while (f) {
 		for (i = 0; i < f->num_blocks; i++)
-			free_page((unsigned long)(f->blocks[i].data));
+			kmem_cache_free(flash_block_cache, f->blocks[i].data);
 		next = f->next;
-		free_page((unsigned long)f);
+		kmem_cache_free(flash_block_cache, f);
 		f = next;
 	}
 }
···
 	return msglen;
 }
 
+/* constructor for flash_block_cache */
+void rtas_block_ctor(void *ptr, kmem_cache_t *cache, unsigned long flags)
+{
+	memset(ptr, 0, RTAS_BLK_SIZE);
+}
+
 /* We could be much more efficient here.  But to keep this function
  * simple we allocate a page to the block list no matter how small the
  * count is.  If the system is low on memory it will be just as well
···
 	 * proc file
 	 */
 	if (uf->flist == NULL) {
-		uf->flist = (struct flash_block_list *) get_zeroed_page(GFP_KERNEL);
+		uf->flist = kmem_cache_alloc(flash_block_cache, GFP_KERNEL);
 		if (!uf->flist)
 			return -ENOMEM;
 	}
···
 	next_free = fl->num_blocks;
 	if (next_free == FLASH_BLOCKS_PER_NODE) {
 		/* Need to allocate another block_list */
-		fl->next = (struct flash_block_list *)get_zeroed_page(GFP_KERNEL);
+		fl->next = kmem_cache_alloc(flash_block_cache, GFP_KERNEL);
 		if (!fl->next)
 			return -ENOMEM;
 		fl = fl->next;
 		next_free = 0;
 	}
 
-	if (count > PAGE_SIZE)
-		count = PAGE_SIZE;
-	p = (char *)get_zeroed_page(GFP_KERNEL);
+	if (count > RTAS_BLK_SIZE)
+		count = RTAS_BLK_SIZE;
+	p = kmem_cache_alloc(flash_block_cache, GFP_KERNEL);
 	if (!p)
 		return -ENOMEM;
 	
 	if(copy_from_user(p, buffer, count)) {
-		free_page((unsigned long)p);
+		kmem_cache_free(flash_block_cache, p);
 		return -EFAULT;
 	}
 	fl->blocks[next_free].data = p;
···
 		goto cleanup;
 
 	rtas_flash_term_hook = rtas_flash_firmware;
+
+	flash_block_cache = kmem_cache_create("rtas_flash_cache",
+				RTAS_BLK_SIZE, RTAS_BLK_SIZE, 0,
+				rtas_block_ctor, NULL);
+	if (!flash_block_cache) {
+		printk(KERN_ERR "%s: failed to create block cache\n",
+				__FUNCTION__);
+		rc = -ENOMEM;
+		goto cleanup;
+	}
 	return 0;
 
 cleanup:
···
 void __exit rtas_flash_cleanup(void)
 {
 	rtas_flash_term_hook = NULL;
+
+	if (flash_block_cache)
+		kmem_cache_destroy(flash_block_cache);
+
 	remove_flash_pde(firmware_flash_pde);
 	remove_flash_pde(firmware_update_pde);
 	remove_flash_pde(validate_pde);