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xen-devel
Re: [Xen-devel][PATCH][VT-d] Dis-allow PCI device assignment if PoD is e
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To: |
"Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx> |
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Subject: |
Re: [Xen-devel][PATCH][VT-d] Dis-allow PCI device assignment if PoD is enabled |
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From: |
George Dunlap <george.dunlap@xxxxxxxxxxxxx> |
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Date: |
Thu, 21 Jan 2010 13:45:33 +0000 |
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Cc: |
Keir, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>, Fraser <Keir.Fraser@xxxxxxxxxxxxx>, "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> |
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Thu, 21 Jan 2010 05:46:06 -0800 |
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Thunderbird 2.0.0.23 (X11/20090817) |
Seems like a good "seatbelt" for 4.0.
Looking forward, what would it take to make PoD and VT-d coexist? We
only need PoD during boot, until the balloon driver comes up and
balloons down the guest's memory. Three solutions come to mind, but as
I don't know the constraints of VT-d, I don't know which is feasible (if
any):
* Redo the VT-d mapping every time the p2m map changes as a result of PoD.
* While PoD pages exist, intercept device commands, and redo the VT-d
map if the page was marked PoD the last time we updated the VT-d map
* Detect DMA faults, instantiate the page if necessary, update the VT-d
map, and re-start the transaction.
How expensive is it to change the VT-d pagetable? Is a DMA fault
re-startable? i.e., could we take a fault, redo the VT-d map, and
re-issue the DMA request?
-George
Xu, Dongxiao wrote:
It seems that currently we don't have any code to handle
the coexistence of VT-d and PoD. VT-d engine needs to set up
the entire page table for the domain. However if PoD is enabled,
un-populated memory is marked as populate_on_demand, and
VT-d engine won't set up page tables for them. Therefore any
DMA towards those memory may cause DMA fault.
So for safety concern, its better to dis-allow PCI device
assignment if PoD is enabled.
Best Regards,
-- Dongxiao
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