block: sed-opal: kmalloc the cmd/resp buffers

In accordance with [1] the DMA-able memory buffers must be
cacheline-aligned otherwise the cache writing-back and invalidation
performed during the mapping may cause the adjacent data being lost. It's
specifically required for the DMA-noncoherent platforms [2]. Seeing the
opal_dev.{cmd,resp} buffers are implicitly used for DMAs in the NVME and
SCSI/SD drivers in framework of the nvme_sec_submit() and sd_sec_submit()
methods respectively they must be cacheline-aligned to prevent the denoted
problem. One of the option to guarantee that is to kmalloc the buffers
[2]. Let's explicitly allocate them then instead of embedding into the
opal_dev structure instance.

Note this fix was inspired by the commit c94b7f9 ("nvme-hwmon:
kmalloc the NVME SMART log buffer").

[1] Documentation/core-api/dma-api.rst
[2] Documentation/core-api/dma-api-howto.rst

Fixes: 455a7b2 ("block: Add Sed-opal library")
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221107203944.31686-1-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/sed-opal.c

@@ -87,8 +87,8 @@ struct opal_dev {
 	u64 lowest_lba;
 
 	size_t pos;
-	u8 cmd[IO_BUFFER_LENGTH];
-	u8 resp[IO_BUFFER_LENGTH];
+	u8 *cmd;
+	u8 *resp;
 
 	struct parsed_resp parsed;
 	size_t prev_d_len;
@@ -2175,6 +2175,8 @@ void free_opal_dev(struct opal_dev *dev)
 		return;
 
 	clean_opal_dev(dev);
+	kfree(dev->resp);
+	kfree(dev->cmd);
 	kfree(dev);
 }
 EXPORT_SYMBOL(free_opal_dev);
@@ -2187,18 +2189,40 @@ struct opal_dev *init_opal_dev(void *data, sec_send_recv *send_recv)
 	if (!dev)
 		return NULL;
 
+	/*
+	 * Presumably DMA-able buffers must be cache-aligned. Kmalloc makes
+	 * sure the allocated buffer is DMA-safe in that regard.
+	 */
+	dev->cmd = kmalloc(IO_BUFFER_LENGTH, GFP_KERNEL);
+	if (!dev->cmd)
+		goto err_free_dev;
+
+	dev->resp = kmalloc(IO_BUFFER_LENGTH, GFP_KERNEL);
+	if (!dev->resp)
+		goto err_free_cmd;
+
 	INIT_LIST_HEAD(&dev->unlk_lst);
 	mutex_init(&dev->dev_lock);
 	dev->flags = 0;
 	dev->data = data;
 	dev->send_recv = send_recv;
 	if (check_opal_support(dev) != 0) {
 		pr_debug("Opal is not supported on this device\n");
-		kfree(dev);
-		return NULL;
+		goto err_free_resp;
 	}
 
 	return dev;
+
+err_free_resp:
+	kfree(dev->resp);
+
+err_free_cmd:
+	kfree(dev->cmd);
+
+err_free_dev:
+	kfree(dev);
+
+	return NULL;
 }
 EXPORT_SYMBOL(init_opal_dev);