Re: [Xen-devel] ARM Guest VM Type

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sat, 2014-04-26 at 15:17 +0100, Stefano Stabellini wrote:
> On Fri, 25 Apr 2014, Wei Huang wrote:
> > According to enlighten.c in Kernel, ARM DomU is considered as HVM domain.
> > However when the DomU is created, its property isn't configured to reflect
> > this (XEN_DOMCTL_CDF_xxx) in tools. So is_hvm_domain(d) will return FALSE
> > inside hypervisor.
> > 
> > Error?
> 
> It is not really an error, more an inconsistency. In reality the old
> "PV" and "HVM" labels don't fit ARM guests very well.
> 
> From Linux POV it makes sense to think of ARM guests as HVM guests.
> If it makes sense to do the same in Xen, then we might as well set the
> flag.

The "PV" and "HVM" labels are x86 specific and have no real bearing on
the ARM hypervisor. We've been slowly eliminating the is_{pv,hvm}_foo
calls from the generic code in the hypervisor in favour of more specific
functionality tests (often paging-mode-translate based ones). We should
continue to do this cleanup, setting any kind of PV or HVM based flag
for an ARM guest would be wrong.

IMHO we should be doing the same on Linux (and all guest kernels) as
well, but the leakage of x86-isms into the generic code is more
pervasive there it seems (although I hope that between ARM and x86 PVH
we can eventually clean it up there too)

Ian.


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