From: Clemens Ladisch <clemens@ladisch.de>
To: stefanr@s5r6.in-berlin.de
Cc: Hector Martin <marcan@marcan.st>,
linux1394-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] firewire-ohci: work around oversized DMA reads on JMicron controllers
Date: Fri, 3 Nov 2017 15:21:30 +0100 [thread overview]
Message-ID: <554bac12-e021-2541-6812-ae9a4e0c96ba@ladisch.de> (raw)
In-Reply-To: <20171103112857.12426-1-marcan@marcan.st>
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 <marcan@marcan.st>
Reviewed-by: Clemens Ladisch <clemens@ladisch.de>
> ---
> 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;
>
next prev parent reply other threads:[~2017-11-03 14:21 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-03 11:28 [PATCH] firewire-ohci: work around oversized DMA reads on JMicron controllers Hector Martin
2017-11-03 14:21 ` Clemens Ladisch [this message]
2017-11-12 21:05 ` Stefan Richter
2018-01-11 2:31 ` Hector Martin 'marcan'
2018-01-13 16:55 ` Stefan Richter
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