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Re: [Xen-devel] [v7][PATCH 13/16] libxl: construct e820 map with RDM information for HVM guest

On Tue, 2015-07-14 at 13:44 +0800, Chen, Tiejun wrote:
> On 2015/7/13 18:15, Ian Campbell wrote:
> > On Mon, 2015-07-13 at 17:47 +0800, Chen, Tiejun wrote:
> >>> This approach looks like it should work, and I think given the point in
> >>> the release it would be acceptable for 4.6.
> >>>
> >>> However long term I think it might make sense to try and reuse one of
> >>> the existing libxl__arch hooks, i.e.
> >>> libxl__arch_domain_init_hw_description or
> >>> libxl__arch_domain_finalise_hw_description. On ARM these are to do with
> >>> setting the Device Tree Blob, which included the memory map, so it is
> >>> somewhat morally equivalent to configuring the e820 on x86, I think.
> >>>
> >>> Those hooks are only called from libxl__build_pv today, but calling them
> >>> from libxl__build_hvm seems like it would be good too.
> >>
> >> But seems this is raising some potential risks, isn't this? Although
> >> libxl__arch_domain_init_hw_description() and
> >> libxl__arch_domain_finalise_hw_description() are NOP to x86, they're
> >> really working on ARM side. So if we call them inside
> >> libxl__build_hvm(), any affects to ARM? I'm not very sure at this point
> >> unless anyone can validate this change on ARM, or you really ensure my
> >> concerns is unnecessary.
> >
> > All ARM guests use the PV code path so there is no risk.
> Okay but please take a close look at this,
> libxl__build_pv(gc, domid, info, state)
>      |
>      + libxl__arch_domain_finalise_hw_description(libxl__gc *gc,
>                                        libxl_domain_build_info *info,
>                                        struct xc_dom_image *dom)
> But in our case we need this parameter, struct xc_hvm_build_args *args, 
> so how can we handle this conflict? Its not easy to add this, and it 
> doesn't make sense as well in pv case.

This is an internal API, you can feel free to modify it as necessary.

Please note that I started this subthread with "However long term I
think it might make sense ...", This was not a request to redo this
patch now.


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