patch "usb-storage: Add a limitation for blk_queue_max_hw_sectors()" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb-storage: Add a limitation for blk_queue_max_hw_sectors()

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From d74ffae8b8dd17eaa8b82fc163e6aa2076dc8fb1 Mon Sep 17 00:00:00 2001
From: Yoshihiro Shimoda <[email protected]>
Date: Mon, 22 Jul 2019 19:58:25 +0900
Subject: usb-storage: Add a limitation for blk_queue_max_hw_sectors()

This patch fixes an issue that the following error happens on swiotlb environment:

	xhci-hcd ee000000.usb: swiotlb buffer is full (sz: 524288 bytes), total 32768 (slots), used 1338 (slots)

On the kernel v5.1, block settings of a usb-storage with SuperSpeed were the following so that the block layer will allocate buffers up to 64 KiB, and then the issue didn't happen.

	max_segment_size = 65536
	max_hw_sectors_kb = 1024

After the commit 09324d32d2a0 ("block: force an unlimited segment size on queues with a virt boundary") is applied, the block settings are the following. So, the block layer will allocate buffers up to 1024 KiB, and then the issue happens:

	max_segment_size = 4294967295
	max_hw_sectors_kb = 1024

To fix the issue, the usb-storage driver checks the maximum size of a mapping for the device and then adjusts the max_hw_sectors_kb if required. After this patch is applied, the block settings will be the following, and then the issue doesn't happen.

	max_segment_size = 4294967295
	max_hw_sectors_kb = 256

---
 drivers/usb/storage/scsiglue.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

index 30790240aec6..05b80211290d 100644
@@ -28,6 +28,8 @@
  * status of a command.
  */
 
+#include <linux/blkdev.h>
+#include <linux/dma-mapping.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 

@@ -99,6 +101,7 @@ static int slave_alloc (struct scsi_device *sdev)
 static int slave_configure(struct scsi_device *sdev)
 {
 	struct us_data *us = host_to_us(sdev->host);
+	struct device *dev = us->pusb_dev->bus->sysdev;
 
 	/*
 	 * Many devices have trouble transferring more than 32KB at a time,

@@ -128,6 +131,14 @@ static int slave_configure(struct scsi_device *sdev)
 		blk_queue_max_hw_sectors(sdev->request_queue, 2048);
 	}
 
+	/*
+	 * The max_hw_sectors should be up to maximum size of a mapping for
+	 * the device. Otherwise, a DMA API might fail on swiotlb environment.
+	 */
+	blk_queue_max_hw_sectors(sdev->request_queue,
+		min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
+		      dma_max_mapping_size(dev) >> SECTOR_SHIFT));
+
 	/*
 	 * Some USB host controllers can't do DMA; they have to use PIO.
 	 * They indicate this by setting their dma_mask to NULL.  For

2.22.0