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Re: [Qemu-devel] [PATCH v7 0/5] IOMMU: intel_iommu support map and unmap


From: Lan Tianyu
Subject: Re: [Qemu-devel] [PATCH v7 0/5] IOMMU: intel_iommu support map and unmap notifications
Date: Tue, 6 Dec 2016 15:06:20 +0800
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

On 2016年12月06日 14:51, Peter Xu wrote:
> 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?

First case I think of is nest virtualization and we assign physical
device to l2 guest. User space driver(E.G DPDK) also can enable/disable
IOVA for device dynamically.

-- 
Best regards
Tianyu Lan



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