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Date: Tue, 6 Dec 2016 14:51:55 +0800
From: Peter Xu <peterx@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v7 0/5] IOMMU: intel_iommu support map and
 unmap notifications
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To: Lan Tianyu <tianyu.lan@intel.com>
Cc: "Aviv B.D" <bd.aviv@gmail.com>, qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>, Alex Williamson <alex.williamson@redhat.com>, Jason Wang <jasowang@redhat.com>, "Liu, Yi L" <yi.l.liu@intel.com>, "Wu, Fengguang" <fengguang.wu@intel.com>

On Tue, Dec 06, 2016 at 02:30:24PM +0800, Lan Tianyu wrote:

[...]

> >> 2. How to restore GPA->HPA mapping when IOVA is disabled by guest.
> >> When guest enables IOVA for device, vIOMMU will invalidate all previous
> >> GPA->HPA mapping and update IOVA->HPA mapping to pIOMMU via iommu
> >> notifier. But if IOVA is disabled, I think we should restore GPA->HPA
> >> mapping for the device otherwise the device won't work again in the VM.
> > 
> > If we can have a workable replay mechanism, this problem will be
> > solved IMHO.
> 
> Basic idea is to replay related memory regions to restore GPA->HPA
> mapping when guest disables IOVA.

Btw, could you help elaborate in what case we will trigger such a
condition? Or, can we dynamically enable/disable an IOMMU?

Thanks,

-- peterx