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Re: [Qemu-devel] [PATCH 13/13] pseries: Implement IOMMU and DMA for PAPR
From: |
Benjamin Herrenschmidt |
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 |
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.
- [Qemu-devel] [PATCH 01/13] Use DMADirection type for dma_bdrv_io, (continued)
- [Qemu-devel] [PATCH 06/13] usb-ohci: Use universal DMA helper functions, David Gibson, 2012/03/09
- [Qemu-devel] [PATCH 03/13] usb-xhci: Use PCI DMA helper functions, David Gibson, 2012/03/09
- [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, David Gibson, 2012/03/09
- Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, Paolo Bonzini, 2012/03/09
- Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, David Gibson, 2012/03/13
- Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, Alexander Graf, 2012/03/13
- Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, David Gibson, 2012/03/13
- Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, Alexander Graf, 2012/03/13
- Re: [Qemu-devel] [PATCH 10/13] iommu: Introduce IOMMU emulation infrastructure, David Gibson, 2012/03/14