Messages in this thread | | | From | Casey Leedom <> | Subject | Re: DMA error when sg->offset value is greater than PAGE_SIZE in Intel IOMMU | Date | Mon, 25 Sep 2017 20:19:21 +0000 |
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| From: David Woodhouse <dwmw2@infradead.org> | Sent: Monday, September 25, 2017 11:45 AM | | On Wed, 2017-09-20 at 16:01 +0800, Herbert Xu wrote: | > Harsh Jain <Harsh@chelsio.com> wrote: | > > | > > While debugging DMA mapping error in chelsio crypto driver we | > observed that when scatter/gather list received by driver has some | > entry with page->offset > 4096 (PAGE_SIZE). It starts giving DMA | > error. Without IOMMU it works fine. | > | > This is not a bug. The network stack can and will feed us such | > SG lists. | | Hm? Under what circumstances is the offset permitted to be > | PAGE_SIZE?
As I noted earlier, this is an area of the kernel with which I'm not super familiar. Both Herbert Xu and our local VM Expert have said that having Scatter/Gather Lists with Offsets greater than Page Size is not a bug ...
I'm mostly trying to help out keeping focus on this because Harsh is in India (presumable enjoying a good night's sleep while we look at this. Hopefully we'll have a present of a bug fix for him when he wakes up ... :-)
Casey
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