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Re: [Xen-devel] [PATCH net v4] xen-netback: Fix grant ref resolution in RX path

On Thu, 2014-05-15 at 11:08 +0100, Zoltan Kiss wrote:
> The original series for reintroducing grant mapping for netback had a patch 
> [1]
> to handle receiving of packets from an another VIF. Grant copy on the 
> receiving
> side needs the grant ref of the page to set up the op.
> The original patch assumed (wrongly) that the frags array haven't changed. In
> the case reported by Sander, the sending guest sent a packet where the linear
> buffer and the first frag were under PKT_PROT_LEN (=128) bytes.
> xenvif_tx_submit() then pulled up the linear area to 128 bytes, and ditched 
> the
> first frag. The receiving side had an off-by-one problem when gathered the 
> grant
> refs.
> This patch fixes that by checking whether the actual frag's page pointer is 
> the
> same as the page in the original frag list. It can handle any kind of changes 
> on
> the original frags array, like:
> - removing granted frags from the array at any point
> - adding local pages to the frags list anywhere
> - reordering the frags
> It's optimized to the most common case, when there is 1:1 relation between the
> frags and the list, plus works optimal when frags are removed from the end or
> the beginning.
> [1]: 3e2234: xen-netback: Handle foreign mapped pages on the guest RX path
> Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

(Remind me, do we need both this and Eric's fix, or is it either/or?)

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