From: Christoph Hellwig <hch@infradead.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christoph Hellwig <hch@infradead.org>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
"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: Sun, 15 Apr 2018 05:11:57 -0700 [thread overview]
Message-ID: <20180415121157.GA17726@infradead.org> (raw)
In-Reply-To: <1523003838.21446.238.camel@kernel.crashing.org>
On Fri, Apr 06, 2018 at 06:37:18PM +1000, Benjamin Herrenschmidt wrote:
> > > 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.
>
> Fine with using a dma API always on the Linux side, but we do want to
> special case virtio still at the arch and qemu side to have a "direct
> mapping" mode. Not sure how (special flags on PCI devices) to avoid
> actually going through an emulated IOMMU on the qemu side, because that
> slows things down, esp. with vhost.
>
> IE, we can't I think just treat it the same as a physical device.
We should have treated it like a physical device from the start, but
that device has unfortunately sailed.
But yes, we'll need a per-device quirk that says 'don't attach an
iommu'.
WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: robh@kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
Christoph Hellwig <hch@infradead.org>,
joe@perches.com, david@gibson.dropbear.id.au,
linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net,
Anshuman Khandual <khandual@linux.vnet.ibm.com>
Subject: Re: [RFC] virtio: Use DMA MAP API for devices without an IOMMU
Date: Sun, 15 Apr 2018 05:11:57 -0700 [thread overview]
Message-ID: <20180415121157.GA17726@infradead.org> (raw)
In-Reply-To: <1523003838.21446.238.camel@kernel.crashing.org>
On Fri, Apr 06, 2018 at 06:37:18PM +1000, Benjamin Herrenschmidt wrote:
> > > 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.
>
> Fine with using a dma API always on the Linux side, but we do want to
> special case virtio still at the arch and qemu side to have a "direct
> mapping" mode. Not sure how (special flags on PCI devices) to avoid
> actually going through an emulated IOMMU on the qemu side, because that
> slows things down, esp. with vhost.
>
> IE, we can't I think just treat it the same as a physical device.
We should have treated it like a physical device from the start, but
that device has unfortunately sailed.
But yes, we'll need a per-device quirk that says 'don't attach an
iommu'.
next prev parent reply other threads:[~2018-04-15 12:37 UTC|newest]
Thread overview: 29+ 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 11:14 ` Balbir Singh
2018-04-05 11:28 ` Anshuman Khandual
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 18:34 ` Michael S. Tsirkin
2018-04-05 21:18 ` Benjamin Herrenschmidt
2018-04-05 21:18 ` Benjamin Herrenschmidt
2018-04-06 2:53 ` Anshuman Khandual
2018-04-06 2:53 ` Anshuman Khandual
2018-04-06 7:16 ` Christoph Hellwig
2018-04-06 8:37 ` Benjamin Herrenschmidt
2018-04-06 8:37 ` Benjamin Herrenschmidt
2018-04-15 12:11 ` Christoph Hellwig [this message]
2018-04-15 12:11 ` Christoph Hellwig
2018-04-18 3:17 ` Anshuman Khandual
2018-04-18 3:17 ` Anshuman Khandual
2018-04-18 16:20 ` Michael S. Tsirkin
2018-05-01 16:34 ` Ram Pai
2018-04-18 16:20 ` Michael S. Tsirkin
2018-04-06 7:16 ` Christoph Hellwig
2018-04-05 15:09 ` Benjamin Herrenschmidt
2018-04-05 14:54 ` Michael S. Tsirkin
2018-04-05 14:39 ` Anshuman Khandual
-- strict thread matches above, loose matches on Subject: below --
2018-04-05 10:56 Anshuman Khandual
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