From: Paolo Bonzini <pbonzini@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, Andy Lutomirski <luto@kernel.org>
Cc: linux-kernel@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>,
sparclinux@vger.kernel.org, Joerg Roedel <jroedel@suse.de>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cornelia.huck@de.ibm.com>,
Sebastian Ott <sebott@linux.vnet.ibm.com>,
Christoph Hellwig <hch@lst.de>,
benh@kernel.crashing.org, KVM <kvm@vger.kernel.org>,
dwmw2@infradead.org, Martin Schwidefsky <schwidefsky@de.ibm.com>,
linux-s390 <linux-s390@vger.kernel.org>,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v4 0/6] virtio core DMA API conversion
Date: Mon, 9 Nov 2015 13:27:57 +0100 [thread overview]
Message-ID: <5640914D.6070401@redhat.com> (raw)
In-Reply-To: <20151109133624-mutt-send-email-mst@redhat.com>
On 09/11/2015 13:15, Michael S. Tsirkin wrote:
> Well that's not exactly true. I think we would like to make
> it possible to put virtio devices behind an IOMMU on x86,
> but if this means existing guests break, then many people won't be able
> to use this option: having to find out which kernel version your guest
> is running is a significant burden.
>
> So on the host side, we need to detect guests that
> don't program the IOMMU and make QEMU ignore it.
> I think we need to figure out a way to do this
> before we commit to the guest change.
What is the usecase for putting virtio devices behind an IOMMU, apart from:
1) "because you can"
2) using VFIO within the guest
? Case 1 can be ignored, and in case 2 the guest will do the right thing.
> Additionally, IOMMU overhead is very high when running within the VM.
> So for uses such as VFIO, we'd like a way to make something like
> iommu-pt the default.
That's not something that the kernel cares about. It's just a
configuration issue.
Paolo
next prev parent reply other threads:[~2015-11-09 12:28 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-30 1:09 [PATCH v4 0/6] virtio core DMA API conversion Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 1/6] virtio-net: Stop doing DMA from the stack Andy Lutomirski
2015-10-30 13:55 ` Christian Borntraeger
2015-10-31 5:02 ` Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 2/6] virtio_ring: Support DMA APIs Andy Lutomirski
2015-10-30 12:01 ` Cornelia Huck
2015-10-30 12:05 ` Christian Borntraeger
2015-10-30 18:51 ` Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 3/6] virtio_pci: Use the DMA API Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 4/6] virtio: Add improved queue allocation API Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 5/6] virtio_mmio: Use the DMA API Andy Lutomirski
2015-10-30 1:09 ` [PATCH v4 6/6] virtio_pci: " Andy Lutomirski
2015-10-30 1:17 ` [PATCH v4 0/6] virtio core DMA API conversion Andy Lutomirski
2015-10-30 9:57 ` Christian Borntraeger
2015-11-09 12:15 ` Michael S. Tsirkin
2015-11-09 12:27 ` Paolo Bonzini [this message]
2015-11-09 22:58 ` Benjamin Herrenschmidt
2015-11-10 0:46 ` Andy Lutomirski
2015-11-10 2:04 ` Benjamin Herrenschmidt
2015-11-10 2:18 ` Andy Lutomirski
2015-11-10 5:26 ` Benjamin Herrenschmidt
2015-11-10 5:33 ` Andy Lutomirski
2015-11-10 5:28 ` Benjamin Herrenschmidt
2015-11-10 5:35 ` Andy Lutomirski
2015-11-10 10:37 ` Benjamin Herrenschmidt
2015-11-10 12:43 ` Michael S. Tsirkin
2015-11-10 19:37 ` Benjamin Herrenschmidt
2015-11-10 18:54 ` Andy Lutomirski
2015-11-10 22:27 ` Benjamin Herrenschmidt
2015-11-10 23:44 ` Andy Lutomirski
2015-11-11 0:44 ` Benjamin Herrenschmidt
2015-11-11 4:46 ` Andy Lutomirski
2015-11-11 5:08 ` Benjamin Herrenschmidt
2015-11-10 7:28 ` Jan Kiszka
2015-11-10 9:45 ` Knut Omang
2015-11-10 10:26 ` Benjamin Herrenschmidt
2015-11-10 10:27 ` Joerg Roedel
2015-11-10 19:36 ` Benjamin Herrenschmidt
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