linux-kernel - Re: [PATCH v4 1/6] virtio-net: Stop doing DMA from the stack

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Date:	Fri, 30 Oct 2015 22:02:17 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	sparclinux@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	KVM <kvm@...r.kernel.org>, David Woodhouse <dwmw2@...radead.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v4 1/6] virtio-net: Stop doing DMA from the stack

On Fri, Oct 30, 2015 at 6:55 AM, Christian Borntraeger
<borntraeger@...ibm.com> wrote:
> Am 30.10.2015 um 02:09 schrieb Andy Lutomirski:
>> From: "Michael S. Tsirkin" <mst@...hat.com>
>>
>> Once virtio starts using the DMA API, we won't be able to safely DMA
>> from the stack.  virtio-net does a couple of config DMA requests
>> from small stack buffers -- switch to using dynamically-allocated
>> memory.
>>
>> This should have no effect on any performance-critical code paths.
>>
>> [I wrote the subject and commit message.  mst wrote the code. --luto]
>>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>
> I still get an error when using multiqueue:
>
> #  ethtool -L eth0 combined 4
> [   33.534686] virtio_ccw 0.0.000d: DMA-API: device driver maps memory from stack [addr=00000000629e7c06]

Fixed in my branch, I think.

--Andy
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