From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751285AbdKLVQt (ORCPT ); Sun, 12 Nov 2017 16:16:49 -0500 Received: from einhorn.in-berlin.de ([192.109.42.8]:60985 "EHLO einhorn-mail.in-berlin.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750960AbdKLVQr (ORCPT ); Sun, 12 Nov 2017 16:16:47 -0500 X-Greylist: delayed 636 seconds by postgrey-1.27 at vger.kernel.org; Sun, 12 Nov 2017 16:16:47 EST X-Envelope-From: stefanr@s5r6.in-berlin.de Date: Sun, 12 Nov 2017 22:05:29 +0100 From: Stefan Richter To: Hector Martin , Clemens Ladisch Cc: linux1394-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] firewire-ohci: work around oversized DMA reads on JMicron controllers Message-ID: <20171112220529.4cf6c5b5@kant> In-Reply-To: <554bac12-e021-2541-6812-ae9a4e0c96ba@ladisch.de> References: <20171103112857.12426-1-marcan@marcan.st> <554bac12-e021-2541-6812-ae9a4e0c96ba@ladisch.de> X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > > Reviewed-by: Clemens Ladisch 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/