netdev - Re: [PATCH V4 00/13] x86/Hyper-V: Add Hyper-V Isolation VM support

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Date:   Mon, 30 Aug 2021 14:00:36 +0200
From:   Christoph Hellwig <hch@....de>
To:     Tianyu Lan <ltykernel@...il.com>
Cc:     kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
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Subject: Re: [PATCH V4 00/13] x86/Hyper-V: Add Hyper-V Isolation VM support

Sorry for the delayed answer, but I look at the vmap_pfn usage in the
previous version and tried to come up with a better version.  This
mostly untested branch:

http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/hyperv-vmap

get us there for swiotlb and the channel infrastructure  I've started
looking at the network driver and didn't get anywhere due to other work.

As far as I can tell the network driver does gigantic multi-megabyte
vmalloc allocation for the send and receive buffers, which are then
passed to the hardware, but always copied to/from when interacting
with the networking stack.  Did I see that right?  Are these big
buffers actually required unlike the normal buffer management schemes
in other Linux network drivers?

If so I suspect the best way to allocate them is by not using vmalloc
but just discontiguous pages, and then use kmap_local_pfn where the
PFN includes the share_gpa offset when actually copying from/to the
skbs.