Message-ID: <5540E71E.2050200@dev.mellanox.co.il>
Date: Wed, 29 Apr 2015 17:13:50 +0300
From: Ido Shamay <idos@dev.mellanox.co.il>
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To: David Daney <ddaney.cavm@gmail.com>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>
CC: Roland Dreier <roland@kernel.org>, Sean Hefty <sean.hefty@intel.com>,
        Hal Rosenstock <hal.rosenstock@gmail.com>,
        Amir Vadai <amirv@mellanox.com>, Or Gerlitz <ogerlitz@mellanox.com>,
        Yishai Hadas <yishaih@mellanox.com>, Matan Barak <matanb@mellanox.com>,
        Majd Dibbiny <majd@mellanox.com>,
        Jack Morgenstein <jackm@dev.mellanox.co.il>,
        Moni Shoua <monis@mellanox.com>,
        Eugenia Emantayev <eugenia@mellanox.co.il>,
        Saeed Mahameed <saeedm@mellanox.com>,
        Yuval Atias <yuvala@mellanox.com>, Maor Gottlieb <maorg@mellanox.com>,
        David Daney <david.daney@cavium.com>
Subject: Re: [PATCH RFC] net/mlx4: Remove improper usage of dma_alloc_coherent().
References: <1428361229-31542-1-git-send-email-ddaney.cavm@gmail.com> <55243362.5040207@dev.mellanox.co.il> <552AE4A4.30005@dev.mellanox.co.il>
In-Reply-To: <552AE4A4.30005@dev.mellanox.co.il>
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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@cavium.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@mellanox.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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