linux-kernel - Re: [PATCH v3 0/3] virtio DMA API core stuff

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Message-ID: <5651F5A0.5060400@redhat.com>
Date:	Sun, 22 Nov 2015 19:04:32 +0200
From:	Marcel Apfelbaum <marcel@...hat.com>
To:	David Woodhouse <dwmw2@...radead.org>,
	Joerg Roedel <jroedel@...e.de>,
	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-s390 <linux-s390@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Andy Lutomirski <luto@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Christoph Hellwig <hch@....de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff

On 11/22/2015 05:54 PM, David Woodhouse wrote:
> On Sun, 2015-11-22 at 15:06 +0200, Marcel Apfelbaum wrote:
>>
>>
>> I tried to generate a DMAR table that excludes some devices from
>> IOMMU translation, however it does not help.
>>
>> The reason is, as far as I understand, that Linux kernel does
>> not allow any device being outside an IOMMU scope if the
>> iommu kernel option is activated.
>>
>> Does anybody know if it is "by design" or is simply an uncommon
>> configuration?
>> (some devices in an IOMMU scope, while others outside *any* IOMMU
>> scope)
>
> That's a kernel bug in the way it handles per-device DMA operations. Or
> more to the point, in the way it doesn't — the non-translated devices
> end up being pointed to the intel_dma_ops despite the fact they
> shouldn't be. I'm working on that...
>

Hi David,
Thank you for the fast response.

Sadly I am not familiar with the DMA/IOMMU code to contribute
with a sane idea, but I'll gladly test it.
If you lack the time and have an idea to share, I can give it a try though.

Thanks,
Marcel


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