From: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
To: David Miller <davem@davemloft.net>
Cc: jeffrey.t.kirsher@intel.com, intel-wired-lan@lists.osuosl.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
cphealy@gmail.com
Subject: Re: igb driver can cause cache invalidation of non-owned memory?
Date: Mon, 10 Oct 2016 12:51:28 +0300 [thread overview]
Message-ID: <10474d19-df1a-3b09-917e-70659be3a56c@cogentembedded.com> (raw)
In-Reply-To: <20161010.050125.1981283393312167625.davem@davemloft.net>
>> With this scheme, page used for Rx is completely dma_map()ed at
>> allocation time, split into two buffers, and individual buffer is
>> sync_to_cpu()ed AND PASSED TO NETWORK STACK via skb_add_rx_frag() -
>> while driver driver still uses other buffer. Later, when driver decides
>> to no longer use this page, it will dma_unmap() it completely - which on
>> archs with non-coherent caches means cache invalidation. This cache
>> invalidation will include area that is already passed elsewhere.
>
> This should happen only if the device wrote into that piece of the
> memory which it absolutely should not.
Hmm... I'm not about device writing to memory.
Sequence in igb driver is:
dma_map(full_page)
<device writes here>
sync_to_cpu(half_page);
skb_add_rx_frag(skb, half_page);
napi_gro_receive(skb);
...
dma_unmap(full_page)
What I'm concerned about is - same area is first passed up to network
stack, and _later_ dma_unmap()ed. Is this indeed safe?
Nikita
next prev parent reply other threads:[~2016-10-10 9:51 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-10 8:52 igb driver can cause cache invalidation of non-owned memory? Nikita Yushchenko
2016-10-10 9:01 ` David Miller
2016-10-10 9:51 ` Nikita Yushchenko [this message]
2016-10-10 11:57 ` David Miller
2016-10-10 12:27 ` Nikita Yushchenko
2016-10-10 12:31 ` Nikita Yushchenko
2016-10-10 15:11 ` Alexander Duyck
2016-10-10 17:00 ` Nikita Yushchenko
2016-10-10 17:38 ` Alexander Duyck
2016-10-12 6:55 ` Nikita Yushchenko
2016-10-12 15:32 ` Alexander Duyck
2016-10-12 16:03 ` David Laight
2016-10-12 16:11 ` Nikita Yushchenko
2016-10-12 17:56 ` Alexander Duyck
2016-10-12 18:12 ` Nikita Yushchenko
2016-10-12 18:30 ` Alexander Duyck
2016-10-13 10:39 ` David Laight
2016-10-13 11:00 ` Nikita Yushchenko
2016-10-13 20:32 ` Alexander Duyck
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