From: Christoph Hellwig <hch@infradead.org>
To: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
robh@kernel.org, aik@ozlabs.ru, jasowang@redhat.com,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org, joe@perches.com,
david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org,
elfring@users.sourceforge.net
Subject: Re: [RFC] virtio: Use DMA MAP API for devices without an IOMMU
Date: Fri, 6 Apr 2018 00:16:34 -0700 [thread overview]
Message-ID: <20180406071634.GA31108@infradead.org> (raw)
In-Reply-To: <70cb433f-a8f7-5199-3c96-a760c7624804@linux.vnet.ibm.com>
On Fri, Apr 06, 2018 at 08:23:10AM +0530, Anshuman Khandual wrote:
> On 04/06/2018 02:48 AM, Benjamin Herrenschmidt wrote:
> > On Thu, 2018-04-05 at 21:34 +0300, Michael S. Tsirkin wrote:
> >>> In this specific case, because that would make qemu expect an iommu,
> >>> and there isn't one.
> >>
> >>
> >> I think that you can set iommu_platform in qemu without an iommu.
> >
> > No I mean the platform has one but it's not desirable for it to be used
> > due to the performance hit.
>
> Also the only requirement is to bounce the I/O buffers through SWIOTLB
> implemented as DMA API which the virtio core understands. There is no
> need for an IOMMU to be involved for the device representation in this
> case IMHO.
This whole virtio translation issue is a mess. I think we need to
switch it to the dma API, and then quirk the legacy case to always
use the direct mapping inside the dma API.
next prev parent reply other threads:[~2018-04-06 7:36 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-05 10:56 [RFC] virtio: Use DMA MAP API for devices without an IOMMU Anshuman Khandual
2018-04-05 11:14 ` Balbir Singh
2018-04-05 11:28 ` Anshuman Khandual
2018-04-05 14:39 ` Anshuman Khandual
2018-04-05 14:54 ` Michael S. Tsirkin
2018-04-05 15:09 ` Benjamin Herrenschmidt
2018-04-05 18:34 ` Michael S. Tsirkin
2018-04-05 21:18 ` Benjamin Herrenschmidt
2018-04-06 2:53 ` Anshuman Khandual
2018-04-06 7:16 ` Christoph Hellwig [this message]
2018-04-06 8:37 ` Benjamin Herrenschmidt
2018-04-15 12:11 ` Christoph Hellwig
2018-04-18 3:17 ` Anshuman Khandual
2018-04-18 16:20 ` Michael S. Tsirkin
2018-05-01 16:34 ` Ram Pai
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