linux-kernel - Re: [PATCH RFC] net/mlx4: Remove improper usage of dma_alloc

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Message-ID: <5540E71E.2050200@dev.mellanox.co.il>
Date:	Wed, 29 Apr 2015 17:13:50 +0300
From:	Ido Shamay <idos@....mellanox.co.il>
To:	David Daney <ddaney.cavm@...il.com>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>
CC:	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Yishai Hadas <yishaih@...lanox.com>,
	Matan Barak <matanb@...lanox.com>,
	Majd Dibbiny <majd@...lanox.com>,
	Jack Morgenstein <jackm@....mellanox.co.il>,
	Moni Shoua <monis@...lanox.com>,
	Eugenia Emantayev <eugenia@...lanox.co.il>,
	Saeed Mahameed <saeedm@...lanox.com>,
	Yuval Atias <yuvala@...lanox.com>,
	Maor Gottlieb <maorg@...lanox.com>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH RFC] net/mlx4: Remove improper usage of dma_alloc_coherent().


On 4/13/2015 12:33 AM, Ido Shamay wrote:
> On 4/7/2015 10:43 PM, Ido Shamay wrote:
>> On 4/7/2015 2:00 AM, David Daney wrote:
>>> From: David Daney <david.daney@...ium.com>
>>>
>>> The dma_alloc_coherent() function returns a virtual address which can
>>> be used for coherent access to the underlying memory.  On some
>>> architectures, like arm64, undefined behavior results if this memory is
>>> also accessed via virtual mappings that are not coherent. Because of
>>> their undefined nature, operations like virt_to_page() return garbage
>>> when passed virtual addresses obtained from dma_alloc_coherent().  Any
>>> subsequent mappings via vmap() of the garbage page values are unusable
>>> and result in bad things like bus errors (synchronous aborts in ARM64
>>> speak).
>>>
>>> The MLX4 driver contains code that does the equivalent of:
>>>
>>>    vmap(virt_to_page(dma_alloc_coherent))
>>>
>>> This results in an OOPs when the device is opened.
>>>
>>> To fix this...
>>>
>>> Always use result of dma_alloc_coherent() directly.
> Acked-by: Ido Shamay <idos@...lanox.com>
> Thanks David, this is good for us

Hi David,

Are you resending this patch or you want us to do that?

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