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/
