Avi Kivity wrote:
> Han, Weidong wrote:
>> [Rebased the patch due to my mmio's patch (commit: 0d679782) was
>> checked in]
>>
>> From 9e68fc762358cc44cfec3968ac5ec65324ce04d7 Mon Sep 17 00:00:00
>> 2001 From: Weidong Han <[EMAIL PROTECTED]>
>> Date: Mon, 6 Oct 2008 14:02:18 +0800
>> Subject: [PATCH] Support multiple device assignment to one guest
>>
>> Current VT-d patches in kvm only support one device assignment to one
>> guest due to dmar_domain is per device.
>>
>> In order to support multiple device assignemnt, this patch wraps
>> dmar_domain with a reference count (kvm_vtd_domain), and also adds a
>> pointer in kvm_assigned_dev_kernel to link to a kvm_vtd_domain.
>>
>> Each dmar_domain owns one VT-d page table, in order to reduce page
>> tables and improve IOTLB utility, the devices assigned to the same
>> guest and under the same IOMMU share the same kvm_vtd_domain.
>>
>>
>
> I don't understand this. If we have a one dmar domain per guest, why
> do we need reference counting at all?
>
> We can create the dmar domain when we assign the first device, and
> destroy it when we deassign the last device, but otherwise I don't
> see a need for changes. Particularly I don't understand this:
>
>> @@ -351,7 +351,6 @@ struct kvm_arch{
>> */
>> struct list_head active_mmu_pages;
>> struct list_head assigned_dev_head;
>> - struct dmar_domain *intel_iommu_domain;
>> struct kvm_pic *vpic;
>> struct kvm_ioapic *vioapic;
>> struct kvm_pit *vpit;
>> @@ -305,6 +310,7 @@ struct kvm_assigned_dev_kernel { int
>> irq_requested; struct pci_dev *dev;
>> struct kvm *kvm;
>> + struct kvm_vtd_domain *vtd_domain;
>> };
>
> Oh, I see it now. Different devices may need to go under different
> iommus.
>
> This really feels like it should be handled by the iommu API. Users
> shouldn't need to bother with it.
Why do you say it should be handled by iommu API? The direct way to
support multiple device assignment is keep a dmar_domain list for each
guest, each device corresponds to one dmar_domain. But this will cost
more memory because each dmar_domain has its own VT-d page table. Our
method lets the devices which are under smae iommu and assigned to the
same guest share the same VT-d page table.
Regards,
Weidong
>
> Joerg, can your dma api handle this?
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