Date: Fri, 3 Nov 2017 20:28:57 +0900 From: Hector Martin Subject: firewire-ohci: work around oversized DMA reads on JMicron controllers 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 Reviewed-by: Clemens Ladisch Signed-off-by: Stefan Richter --- drivers/firewire/ohci.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/drivers/firewire/ohci.c +++ b/drivers/firewire/ohci.c @@ -1130,7 +1130,13 @@ static int context_add_buffer(struct con 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;