On 07.08.2015 15:40, linux-usb@xxxxxxxxxxx wrote:
> Hi there,
Hi
>
>
> Moving from 4.0.4 to 4.0.5, my USB 3.0 controller became practically useless
> (and this same issue persists [at least] upto and including 4.1.3).
> Here's an excerpt from my syslog demonstrating the problem:
>
...
>
> Looking in ChangeLog-4.0.5 for xhci-related changes gave me 3 hits:
>
> (1) xhci: gracefully handle xhci_irq dead device
> commit 948fa13504f80b9765d2b753691ab94c83a10341 upstream.
>
> (2) xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256
> commit 18cc2f4cbbaf825a4fedcf2d60fd388d291e0a38 upstream.
>
> (3) xhci: fix isoc endpoint dequeue from advancing too far on transaction error
> commit d104d0152a97fade389f47635b73a9ccc7295d0b upstream.
>
> The first one seemed fairly irrelevant. The third one mentions DMA, but
> looking at the actual changes, I couldn't see an obvious connection to the
> 'PTE read access' issue. So, I tested reverting the second patch in my
> current (4.1.3) kernel and my USB 3.0 controller started working again.
>
> This is good enough for me, but I thought you might want to look more closely
> at the root cause, and ensure that the PTE is correctly setup even with the
> increased TRBS_PER_SEGMENT.
>
We just found that the TRBS_PER_SEGMENT reveals an old off by one error in an upper boundary check.
Previously a ring segment didn't use a full memory page, and each ring segment was allocated a new page, so the +1 off by one never caused any harm.
Now that we use the full memory page the off by one actually allowed us going past the allocated page.
This is fixed in patch
commit 7895086afde2a05fa24a0e410d8e6b75ca7c8fdd
xhci: fix off by one error in TRB DMA address boundary check
Fix is now in Greg's usb-linus branch, and should end up in linus 4.2 kernel (rc6 earliest)
Does that fix help in your case?
-Mathias
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