Re: Xen virtual IOMMU high level design doc V3

[Lan Tianyu <tianyu.lan@intel.com>]

On 2016年11月21日 15:05, Tian, Kevin wrote:
>> If someone add "intel_iommu=on" kernel parameter manually, IOMMU driver
>> > will panic guest because it can't enable DMA remapping function via gcmd
>> > register and "Translation Enable Status" bit in gsts register is never
>> > set by vIOMMU. This shows actual vIOMMU status that there is no l2
>> > translation support and warn user should not enable l2 translation.
> The rationale of section 3.5 is confusing. Do you mean sth. like below?
> 
> - We can first do IRQ remapping, because DMA remapping (l1/l2) and 
> IRQ remapping can be enabled separately according to VT-d spec. Enabling 
> of DMA remapping will be first emulated as a failure, which may lead
> to guest kernel panic if intel_iommu is turned on in the guest. But it's
> not a big problem because major distributions have DMA remapping
> disabled by default while IRQ remapping is enabled.
> 
> - For DMA remapping, likely you'll enable L2 translation first (there is
> no capability bit) with L1 translation disabled (there is a SVM capability 
> bit). 
> 
> If yes, maybe we can break this design into 3 parts too, so both
> design review and implementation side can move forward step by
> step?
> 

Yes, we may implement IRQ remapping first. I will break this design into
3 parts(interrupt remapping, L2 translation and L1 translation). IRQ
remapping will be first one to be sent out for detail discussion.

-- 
Best regards
Tianyu Lan

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