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SubjectRe: [PATCH] xhci: Cope with VIA VL805 readahead
On 11/10/2017 02:09, Robin Murphy wrote:
> The VIA VL805 host controller is well-known for causing problems on
> systems with IOMMUs enabled, ranging from triggering endless streams of
> fault messages to locking itself up completely. It appears that the root
> of the problem might be an over-aggressive prefetching of TRBs, wherein
> consuming commands near the end of a queue segment causes it to read off
> the end of the segment, even across a page boundary. This blows up when
> DMA mapping ops are backed by an IOMMU, since there is no guarantee that
> addresses outside the allocated segment are accessible at all.
> Some trial-and-error investigation reveals that we can avoid such
> cross-page reads by not using the last few TRBs in a segment; to that
> end, factor out the implicit index of the end-of-segemnt link TRB, and
> implement a quirk to move it slightly further forward when necessary.
> Signed-off-by: Robin Murphy <>
> ---
> drivers/usb/host/xhci-mem.c | 32 +++++++++++++++++++-------------
> drivers/usb/host/xhci-pci.c | 5 +++++
> drivers/usb/host/xhci-ring.c | 10 +++++++++-
> drivers/usb/host/xhci.c | 10 +++++-----
> drivers/usb/host/xhci.h | 2 ++
> 5 files changed, 40 insertions(+), 19 deletions(-)

Seems like the invalid DMA I'm getting on xhci_reset during the xhci driver's
initialisation/probing process isn't the same one you're getting.. This patch
doesn't appear to change that at all.

Oh well.


Hao Wei

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