Re: [Xen-devel] [PATCH v2 3/5] xen/domain: Stricter configuration checking

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Nov 13, 2018 at 07:14:24AM -0700, Jan Beulich wrote:
> >>> On 12.11.18 at 17:16, <andrew.cooper3@xxxxxxxxxx> wrote:
> > Currently, a number of options passed for domain creation are ignored, or 
> > have
> > implicit fallback behaviour.  This is bad for forwards compatibility, and 
> > for
> > end users to be certain that they got the configuration they asked for.
> > 
> > With this change:
> >  * ARM now strictly requires that XEN_DOMCTL_CDF_hap is passed.  Previously,
> >    only XEN_DOMCTL_CDF_hvm_guest was checked.
> >  * For x86, requesting HAP without HVM is now prohibited, as the combination
> >    makes no sense.
> >  * For x86, requesting HAP on a non-HAP capable system will fail, rather 
> > than
> >    silently fall back to Shadow.
> > 
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > ---
> > CC: Jan Beulich <JBeulich@xxxxxxxx>
> > CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> > CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > CC: Julien Grall <julien.grall@xxxxxxx>
> > CC: Ian Jackson <Ian.Jackson@xxxxxxxxxx>
> > CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> > 
> > Semi RFC because this may cause a user-visible change in behaviour.  
> > However,
> > if the user has gone to the effort of specifying hap=1, silently falling 
> > back
> > to shadow is unexpected, and IMO, a bug.
> 
> My view on this to a fair part depends on whether the tool stack
> would guard us from actually getting into such a situation in the
> hypervisor. Getting an unspecific -EINVAL back without further
> help towards diagnosis by the tool stack would make such a
> change undesirable imo.

If you want toolstack to tell you what goes wrong, this sanitisation
function should be shared with the toolstack, and presumably with some
if __XEN_TOOLS__ trickeries to return / print out the culprit.

Wei.

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