RE: How to resolve an issue in swiotlb environment?

Yoshihiro Shimoda
2019-06-10T11:13:14Z

Hi Christoph, Alan,
(add linux-usb ML on CC.)

> From: Yoshihiro Shimoda, Sent: Friday, June 7, 2019 9:00 PM
>
> Hi Christoph,
>
> I think we should continue to discuss on this email thread instead of the fixed DMA-API.txt patch [1]
>
> [1]
> https://marc.info/?t=155989412200001&r=1&w=2
>
> > From: Yoshihiro Shimoda, Sent: Monday, June 3, 2019 3:42 PM
> >
> > Hi linux-block and iommu mailing lists,
> >
> > I have an issue that a USB SSD with xHCI on R-Car H3 causes "swiotlb is full" like below.
> >
> > [ 36.745286] xhci-hcd ee000000.usb: swiotlb buffer is full (sz: 524288 bytes), total 32768 (slots), used 1338
> (slots)
> >
> > I have investigated this issue by using git bisect, and then I found the following commit:
> >
> > ---
> > commit 09324d32d2a0843e66652a087da6f77924358e62
> > Author: Christoph Hellwig <hch@lst.de>
> > Date: Tue May 21 09:01:41 2019 +0200
> >
> > block: force an unlimited segment size on queues with a virt boundary
> > ---
>
> Thank you for your comment on other email thread [2] like below:
> ---
> Turns out it isn't as simple as I thought, as there doesn't seem to
> be an easy way to get to the struct device used for DMA mapping
> from USB drivers. I'll need to think a bit more how to handle that
> best.
> ---
>
> [2]
> https://marc.info/?l=linux-doc&m=155989651620473&w=2

I have another way to avoid the issue. But it doesn't seem that a good way though...
According to the commit that adding blk_queue_virt_boundary() [3],
this is needed for vhci_hcd as a workaround so that if we avoid to call it
on xhci-hcd driver, the issue disappeared. What do you think?
JFYI, I pasted a tentative patch in the end of email [4].

---
[3]
commit 747668dbc061b3e62bc1982767a3a1f9815fcf0e
Author: Alan Stern <stern@rowland.harvard.edu>
Date: Mon Apr 15 13:19:25 2019 -0400

usb-storage: Set virt_boundary_mask to avoid SG overflows
---
[4]
diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index 59190d8..277c6f7e 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -30,6 +30,8 @@

#include <linux/module.h>
#include <linux/mutex.h>
+#include <linux/usb.h>
+#include <linux/usb/hcd.h>

#include <scsi/scsi.h>
#include <scsi/scsi_cmnd.h>
@@ -65,6 +67,7 @@ static const char* host_info(struct Scsi_Host *host)
static int slave_alloc (struct scsi_device *sdev)
{
struct us_data *us = host_to_us(sdev->host);
+ struct usb_hcd *hcd = bus_to_hcd(us->pusb_dev->bus);
int maxp;

/*
@@ -80,8 +83,10 @@ static int slave_alloc (struct scsi_device *sdev)
* Bulk maxpacket value. Fortunately this value is always a
* power of 2. Inform the block layer about this requirement.
*/
- maxp = usb_maxpacket(us->pusb_dev, us->recv_bulk_pipe, 0);
- blk_queue_virt_boundary(sdev->request_queue, maxp - 1);
+ if (!strcmp(hcd->driver->description, "vhci_hcd")) {
+ maxp = usb_maxpacket(us->pusb_dev, us->recv_bulk_pipe, 0);
+ blk_queue_virt_boundary(sdev->request_queue, maxp - 1);
+ }

/*
* Some host controllers may have alignment requirements.
---
Best regards,
Yoshihiro Shimoda