On Nov 03 Clemens Ladisch wrote:
> Hector Martin wrote:
> > At least some JMicron controllers issue buggy oversized DMA reads when
> > fetching context descriptors, always fetching 0x20 bytes at once for
> > descriptors which are only 0x10 bytes long. This is often harmless, but
> > can cause page faults on modern systems with IOMMUs:
> >
> > DMAR: [DMA Read] Request device [05:00.0] fault addr fff56000 [fault reason 06] PTE Read access is not set
> > firewire_ohci 0000:05:00.0: DMA context IT0 has stopped, error code: evt_descriptor_read
> >
> > This works around the problem by always leaving 0x10 padding bytes at
> > the end of descriptor buffer pages, which should be harmless to do
> > unconditionally for controllers in case others have the same behavior.
> >
> > Signed-off-by: Hector Martin <[email protected]>
>
> Reviewed-by: Clemens Ladisch <[email protected]>
Thanks Hector for the troubleshooting and for the patch.
Thanks Clemens for the review.
It's been a while since I last reviewed and tested kernel patches, and
also my main FireWire equipped PC is currently tied up in work for which
reboots aren't desirable. But I am updating a long unused secondary
FireWire'd PC right now and give the patch some testing this week. (This
one even has a JMicron controller, but not an IOMMU.)
> > ---
> > drivers/firewire/ohci.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
> > index 8bf89267dc25..d731b413cb2c 100644
> > --- a/drivers/firewire/ohci.c
> > +++ b/drivers/firewire/ohci.c
> > @@ -1130,7 +1130,13 @@ static int context_add_buffer(struct context *ctx)
> > return -ENOMEM;
> >
> > offset = (void *)&desc->buffer - (void *)desc;
> > - desc->buffer_size = PAGE_SIZE - offset;
> > + /*
> > + * Some controllers, like JMicron ones, always issue 0x20-byte DMA reads
> > + * for descriptors, even 0x10-byte ones. This can cause page faults when
> > + * an IOMMU is in use and the oversized read crosses a page boundary.
> > + * Work around this by always leaving at least 0x10 bytes of padding.
> > + */
> > + desc->buffer_size = PAGE_SIZE - offset - 0x10;
> > desc->buffer_bus = bus_addr + offset;
> > desc->used = 0;
> >
--
Stefan Richter
-======----= =-== -==--
http://arcgraph.de/sr/
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