Re: [Xen-devel] RFC: making the PVH 64bit ABI as stableo

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 2 Jun 2015, Andrew Cooper wrote:
> With my x86 maintainer hat on, the following is an absolute minimum set
> of prerequisite for PVH.
> 
> * 32bit support

Could you please explain why 32bit is important to get PVH out of tech
preview? I don't see 32 bit OSes as an important use case. Maybe there
is more behind it that I cannot see.


> * AMD support

Given that it is pretty difficult for any AMD related changes to affect
the interface, why is this item in the list of things needed to get out
of experimental?


> * Removal of all /* TODO pvhfixme */ from the code
> 
> OTOH, I do not see PCI Passthough or Migration as blockers to tech preview.
> 
> All three of these issues can be addressed by ceasing to think of PVH as
> PV + hardware virt, and by thinking of PVH as HVM without qemu.  At this
> point, PVH and HVM are basically identical from Xens point of view.
> 
> It is my strong oppinion that all PVH guests should start in 32bit flat
> mode (curiously the same as a multiboot entry, hint hint, which I expect
> all mainstream kernels to already have entry points for) at which point
> they can do whatever they like 32/64bit wise and pagetable wise, and we
> are not in the same position as we are with current PV guests where we
> need to know the bitness of them ahead of domain construction.
> 
> ~Andrew
> 

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