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

From: Marcel Apfelbaum <marcel@redhat.com>
To: David Woodhouse <dwmw2@infradead.org>,
	Joerg Roedel <jroedel@suse.de>,
	"Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-s390 <linux-s390@vger.kernel.org>,
	KVM <kvm@vger.kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Sebastian Ott <sebott@linux.vnet.ibm.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Andy Lutomirski <luto@kernel.org>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff
Date: Sun, 22 Nov 2015 19:04:32 +0200	[thread overview]
Message-ID: <5651F5A0.5060400__36023.9258771346$1448343944$gmane$org@redhat.com> (raw)
In-Reply-To: <1448207661.89124.50.camel@infradead.org>

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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