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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: mst@redhat.com, qemu-devel@nongnu.org, agraf@suse.de,
	eduard.munteanu@linux360.ro, Paolo Bonzini <pbonzini@redhat.com>,
	rth@twiddle.net
Subject: Re: [Qemu-devel] [PATCH 13/13] pseries: Implement IOMMU and DMA for PAPR PCI devices
Date: Sun, 11 Mar 2012 13:02:47 +1100	[thread overview]
Message-ID: <1331431367.3105.88.camel@pasglop> (raw)
In-Reply-To: <20120309105847.GA24916@truffala.fritz.box>

On Fri, 2012-03-09 at 21:58 +1100, David Gibson wrote:
> > What about virtio?
> 
> virtio doesn't use virtualized PCI DMA, it uses direct hypervisor
> access to guest memory, by guest physical address.  It *shouldn't*,
> but it does - that's the way it's specced and that's the way the guest
> kernel expects it to be.  It could be fixed with a new feature bit,
> but that's a project for another day.

More precisely, the patch don't break virtio as virtio just bypasses
this all.

Also having virtio go through the iommu might not be such a great idea,
it should definitely remain optional. The ability of virtio to go
straight to guest memory has some significant performance advantages.

Cheers,
Ben.

  reply	other threads:[~2012-03-11  2:03 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-03-09  5:01 [Qemu-devel] [0/13] Implement support for guest visible IOMMUs David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 01/13] Use DMADirection type for dma_bdrv_io David Gibson
2012-03-09  9:34   ` Kevin Wolf
2012-03-09 10:01   ` Paolo Bonzini
2012-03-13  5:53     ` David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 02/13] Better support for dma_addr_t variables David Gibson
2012-03-09 10:00   ` Paolo Bonzini
2012-03-09  5:01 ` [Qemu-devel] [PATCH 03/13] usb-xhci: Use PCI DMA helper functions David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 04/13] Implement cpu_physical_memory_zero() David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 05/13] iommu: Add universal DMA helper functions David Gibson
2012-03-09 10:06   ` Paolo Bonzini
2012-03-09 11:19     ` David Gibson
2012-03-09 11:55       ` Paolo Bonzini
2012-03-09  5:01 ` [Qemu-devel] [PATCH 06/13] usb-ohci: Use " David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 07/13] iommu: Make sglists and dma_bdrv helpers use new universal DMA helpers David Gibson
2012-03-09  9:43   ` Kevin Wolf
2012-03-13 10:42     ` David Gibson
2012-03-13 11:55       ` Kevin Wolf
2012-03-09 10:11   ` Paolo Bonzini
2012-03-13  6:37     ` David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 08/13] ide/ahci: Use universal DMA helper functions David Gibson
2012-03-09  9:48   ` Kevin Wolf
2012-03-10  5:30     ` David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 09/13] usb: Convert usb_packet_{map, unmap} to universal DMA helpers David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure David Gibson
2012-03-09 10:23   ` Paolo Bonzini
2012-03-13  5:07     ` David Gibson
2012-03-13 13:56       ` Alexander Graf
2012-03-13 14:04         ` David Gibson
2012-03-13 14:37           ` Alexander Graf
2012-03-14  9:05             ` David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 11/13] pseries: Convert sPAPR TCEs to use generic IOMMU infrastructure David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 12/13] iommu: Allow PCI to use " David Gibson
2012-03-09  5:01 ` [Qemu-devel] [PATCH 13/13] pseries: Implement IOMMU and DMA for PAPR PCI devices David Gibson
2012-03-09 10:23   ` Paolo Bonzini
2012-03-09 10:58     ` David Gibson
2012-03-11  2:02       ` Benjamin Herrenschmidt [this message]
  -- strict thread matches above, loose matches on Subject: below --
2012-03-22  2:14 [Qemu-devel] [0/13] RFC: Guest visible IOMMU David Gibson
2012-03-22  2:14 ` [Qemu-devel] [PATCH 13/13] pseries: Implement IOMMU and DMA for PAPR PCI devices David Gibson
2012-03-01  5:35 [Qemu-devel] [0/13] RFC: Support for guest-visible IOMMUs David Gibson
2012-03-01  5:36 ` [Qemu-devel] [PATCH 13/13] pseries: Implement IOMMU and DMA for PAPR PCI devices David Gibson

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