netdev - Re: [net-next PATCH v1 1/3] net: sched: af_packet support for direct ring access

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Message-Id: <20141007.120534.1798634446901746809.davem@davemloft.net>
Date:	Tue, 07 Oct 2014 12:05:34 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	danny.zhou@...el.com
Cc:	willemb@...gle.com, john.fastabend@...il.com, dborkman@...hat.com,
	fw@...len.de, gerlitz.or@...il.com, hannes@...essinduktion.org,
	netdev@...r.kernel.org, john.ronciak@...el.com, amirv@...lanox.com,
	eric.dumazet@...il.com
Subject: Re: [net-next PATCH v1 1/3] net: sched: af_packet support for
 direct ring access

From: "Zhou, Danny" <danny.zhou@...el.com>
Date: Tue, 7 Oct 2014 15:21:15 +0000

> Once qpairs split-off is done, the user space driver, as a slave
> driver, will re-initialize those queues completely in user space by
> using paddr(in the case of DPDK, vaddr of DPDK used huge pages are
> translated to paddr) to fill in the packet descriptors.  As of
> security concern raised in previous discussion, the reason we
> think(BTW, correct me if I am wrong) af_packet is most suitable is
> because only user application with root permission is allowed to
> successfully split-off queue pairs and mmap a small window of PCIe
> I/O space to user space, so concern regarding "device can DMA
> from/to any arbitrary physical memory." is not that big. As all user
> space device drivers based on UIO mechanism has the same concern
> issue, VFIO adds protection but it is based on IOMMU which is
> specific to Intel silicons.

Wait a second.

If there is no memory protection performed I'm not merging this.

I thought the user has to associate a fixed pool of memory to the
queueus, the kernel attaches that memory, and then the user cannot
modify the addresses _AT_ _ALL_.

If the user can modify the addresses in the descriptors and make
the chip crap on random memory, this is a non-starter.

Sorry.
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