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Re: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb descript

From: Jason Wang
Subject: Re: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb descriptor
Date: Thu, 16 Feb 2017 13:59:41 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 2017年02月16日 13:43, Jason Wang wrote:

On 2017年02月16日 13:36, Liu, Yi L wrote:
-----Original Message-----
From: Qemu-devel [mailto:address@hidden
On Behalf Of Michael S. Tsirkin
Sent: Tuesday, January 10, 2017 1:40 PM
To: address@hidden
Cc: Peter Maydell <address@hidden>; Eduardo Habkost
<address@hidden>; Jason Wang <address@hidden>; Peter Xu
<address@hidden>; Paolo Bonzini <address@hidden>; Richard
Henderson <address@hidden>
Subject: [Qemu-devel] [PULL 08/41] intel_iommu: support device iotlb

From: Jason Wang <address@hidden>

This patch enables device IOTLB support for intel iommu. The major work is to implement QI device IOTLB descriptor processing and notify the device through
iommu notifier.

Hi Jason/Michael,

Recently Peter Xu's patch also touched intel-iommu emulation. His patch shadows second-level page table by capturing iotlb flush from guest. It would result in page table updating in host. Does this patch also use the same map/umap API provided
by VFIO?

Yes, it depends on the iommu notifier too.

If it is, then I think it would also update page table in host. It looks to be a duplicate update. Pls refer to the following snapshot captured from section
of vtd spec.

"Since translation requests from a device may be serviced by hardware from the IOTLB, software must always request IOTLB invalidation (iotlb_inv_dsc) before requesting corresponding Device-TLB
(dev_tlb_inv_dsc) invalidation."

Maybe for device-iotlb, we need a separate API which just pass down the invalidate
info without updating page table. Any thoughts?

cc Alex.

If we want ATS to be visible for guest (but I'm not sure if VFIO support this), we probably need another notifier or a new flag.


Or need a dedicated address_space if ATS were enabled for the device.

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