From: Ezequiel Garcia <ezequiel.garcia@free-electrons•com>
To: Russell King - ARM Linux <linux@arm•linux.org.uk>
Cc: netdev@vger•kernel.org, David Miller <davem@davemloft•net>,
B38611@freescale•com, fabio.estevam@freescale•com
Subject: Re: [PATCH 2/2] net: mv643xx_eth: Fix highmem support in non-TSO egress path
Date: Wed, 21 Jan 2015 20:34:30 -0300 [thread overview]
Message-ID: <54C03786.2060101@free-electrons.com> (raw)
In-Reply-To: <20150121174049.GW26493@n2100.arm.linux.org.uk>
On 01/21/2015 02:40 PM, Russell King - ARM Linux wrote:
> On Wed, Jan 21, 2015 at 09:54:10AM -0300, Ezequiel Garcia wrote:
>> Commit 69ad0dd7af22b61d9e0e68e56b6290121618b0fb
>> Author: Ezequiel Garcia <ezequiel.garcia@free-electrons•com>
>> Date: Mon May 19 13:59:59 2014 -0300
>>
>> net: mv643xx_eth: Use dma_map_single() to map the skb fragments
>>
>> caused a nasty regression by removing the support for highmem skb
>> fragments. By using page_address() to get the address of a fragment's
>> page, we are assuming a lowmem page. However, such assumption is incorrect,
>> as fragments can be in highmem pages, resulting in very nasty issues.
>>
>> This commit fixes this by using the skb_frag_dma_map() helper,
>> which takes care of mapping the skb fragment properly.
>
> This seems fine, so:
>
I have just realised that the non-TSO and the TSO paths must work
simultaneously (we don't know which path an egress skb will take).
So, with these patches, the unmapping is done using dma_unmap_page() which
is only correct if the skb took the non-TSO paths. In other words,
these fixes are wrong (although I have no idea the effect of
using dma_unmap_page on a mapping done with dma_map_single).
And the problem is that in the TSO path, the linear and the non-linear
fragments use the same kind of descriptors, so we can't distinguish
them in the cleanup, and can't decide if _single or _page should be used.
Any ideas?
I guess we could keep track in some data structure of the type of mapping
on each descriptor. Or alternatively, avoid highmem fragments altogether
by mapping to a lowmem page.
I'll try to come up with some more patches following the first idea.
Sorry for the crappiness,
--
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
next prev parent reply other threads:[~2015-01-21 23:36 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-21 12:54 [PATCH net 0/2] net: marvell: Fix highmem support on non-TSO path Ezequiel Garcia
2015-01-21 12:54 ` [PATCH 1/2] net: mvneta: Fix highmem support in the non-TSO egress path Ezequiel Garcia
2015-01-26 22:40 ` David Miller
2015-01-21 12:54 ` [PATCH 2/2] net: mv643xx_eth: Fix highmem support in " Ezequiel Garcia
2015-01-21 17:40 ` Russell King - ARM Linux
2015-01-21 23:34 ` Ezequiel Garcia [this message]
2015-01-22 0:11 ` Russell King - ARM Linux
2015-01-22 12:17 ` Ezequiel Garcia
2015-01-26 22:40 ` David Miller
2015-01-21 15:01 ` [PATCH net 0/2] net: marvell: Fix highmem support on non-TSO path Russell King - ARM Linux
2015-01-22 18:41 ` Dean Gehnert
2015-01-22 18:45 ` Ezequiel Garcia
2015-01-22 19:01 ` Dean Gehnert
2015-01-22 21:09 ` Russell King - ARM Linux
2015-01-22 21:27 ` Dean Gehnert
2015-01-22 21:49 ` Russell King - ARM Linux
2015-01-22 23:06 ` Russell King - ARM Linux
2015-01-22 23:09 ` Dean Gehnert
2015-01-22 23:08 ` Dean Gehnert
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