RE: [Xen-devel] [PATCH 1/4] xen interface for HVM S3

["Yu, Ke" <ke.yu@xxxxxxxxx>]

Keir Fraser wrote:
> Patches 2 and 3 look okay. Patch 4 is not really useful as it is, as
> you pointed out. And that then raises the question of what *is* the
> usage scenario for this feature? This also raises questions about
> patch 1 -- as it is I think it will need some cleaning up, but if we
> only wanted to do S3 across guest save/restore then we may not need
> Xen changes at all. We simply would not save/restore HVM sate but
> instead have tools manufacture a correct initial HVM state to load
> during restore. Corresponding to a clean initialised system with BP
> about to enter the BIOS. 
> 
>  -- Keir
> 

Yes,  this is good question. 

For the usage scenario, I agree with what Ian Pratt has pointed out. The
most important one is the PCI pass through. Think about if one HVM
domain is directly assigned with physical device, meanwhile, user what
to do host S3.  In this case, Xen must notify HVM domain to do virtual
S3, otherwise, HVM domain will be surprise to see the assigned device is
not working. With the evolution of the PCI passthrouhg technology, e.g.
SR-IOV, we anticipate this scenario will be more and more comon
especially when Xen is used in client side.

Another usage scenario may be extended save/restore. To be honest, we
did not anticipate this usage when design the virtual S3 feature, but
surely we are happy if this feature can be used in this way, which means
this feature is more useful than we expected :)

For patch 1~3, they are basic infrastructure, virtual S3 can not be
achieved without these 3 patches. And please feel free to have cleanup
on patch1.

For the patch4, it is mostly a user interface to call underlying resume
infrastructure which is provided by patch 1~3, we are open on how this
user interface could be. Patch4 just demonstrate how the underlying
infrastructure can be used. And as Ian Pratt has said, probably we can
also implemented "virtual lid" for this purpose in the next step.

Best Regards
Ke


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