Commit 3ae62a42090f ("UAS: fix alignment of scatter/gather segments"),
copying a similar commit for usb-storage, attempted to solve a problem
involving scatter-gather I/O and USB/IP by setting the
virt_boundary_mask for mass-storage devices.

However, it now turns out that the analogous change in usb-storage
interacted badly with commit 09324d32d2a0 ("block: force an unlimited
segment size on queues with a virt boundary"), which was added later.
A typical error message is:

        ehci-pci 0000:00:13.2: swiotlb buffer is full (sz: 327680 bytes),
        total 32768 (slots), used 97 (slots)

There is no longer any reason to keep the virt_boundary_mask setting
in the uas driver.  It was needed in the first place only for
handling devices with a block size smaller than the maxpacket size and
where the host controller was not capable of fully general
scatter-gather operation (that is, able to merge two SG segments into
a single USB packet).  But:

        High-speed or slower connections never use a bulk maxpacket
        value larger than 512;

        The SCSI layer does not handle block devices with a block size
        smaller than 512 bytes;

        All the host controllers capable of SuperSpeed operation can
        handle fully general SG;

        Since commit ea44d190764b ("usbip: Implement SG support to
        vhci-hcd and stub driver") was merged, the USB/IP driver can
        also handle SG.

Therefore all supported device/controller combinations should be okay
with no need for any special virt_boundary_mask.  So in order to head
off potential problems similar to those affecting usb-storage, this
patch reverts commit 3ae62a42090f.

Signed-off-by: Alan Stern <>
CC: Oliver Neukum <>
CC: <>



 drivers/usb/storage/uas.c |   20 --------------------
 1 file changed, 20 deletions(-)

Index: usb-devel/drivers/usb/storage/uas.c
--- usb-devel.orig/drivers/usb/storage/uas.c
+++ usb-devel/drivers/usb/storage/uas.c
@@ -789,30 +789,10 @@ static int uas_slave_alloc(struct scsi_d
        struct uas_dev_info *devinfo =
                (struct uas_dev_info *)sdev->host->hostdata;
-       int maxp;
        sdev->hostdata = devinfo;
-        * We have two requirements here. We must satisfy the requirements
-        * of the physical HC and the demands of the protocol, as we
-        * definitely want no additional memory allocation in this path
-        * ruling out using bounce buffers.
-        *
-        * For a transmission on USB to continue we must never send
-        * a package that is smaller than maxpacket. Hence the length of each
-         * scatterlist element except the last must be divisible by the
-         * Bulk maxpacket value.
-        * If the HC does not ensure that through SG,
-        * the upper layer must do that. We must assume nothing
-        * about the capabilities off the HC, so we use the most
-        * pessimistic requirement.
-        */
-       maxp = usb_maxpacket(devinfo->udev, devinfo->data_in_pipe, 0);
-       blk_queue_virt_boundary(sdev->request_queue, maxp - 1);
-       /*
         * The protocol has no requirements on alignment in the strict sense.
         * Controllers may or may not have alignment restrictions.
         * As this is not exported, we use an extremely conservative guess.

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