Re: [Xen-devel] [PATCH] tools/libxl: Reposition build_pre() logic between architectures

[Julien Grall <julien@xxxxxxx>]

Hi,

On 30/12/2019 13:38, Andrew Cooper wrote:
> On 30/12/2019 13:15, Julien Grall wrote:
> > Hi Andrew,
> >
> > On 27/12/2019 13:45, Andrew Cooper wrote:
> > > The call to xc_domain_disable_migrate() is made only from x86, while its
> > > handling in Xen is common.  Move it to the libxl__build_pre().
> > >
> > > hvm_set_conf_params(), hvm_set_viridian_features(),
> > > hvm_set_mca_capabilities(), and the altp2m logic is all in common
> > > code (parts ifdef'd) but despite this, is all actually x86 specific.
> > While altp2m is only supported on x86, the concept is not
> > x86-specific. I am actually aware of people using altp2m on Arm,
> > althought the support is not upstream yet.
> >
> > > Move it into x86 specific code, and fold all of the
> > > xc_hvm_param_set() calls
> > > together into hvm_set_conf_params() in a far more coherent way.
> > >
> > > Finally - ensure that all hypercalls have their return values checked.
> > >
> > > No practical change in constructed domains.  Fewer useless hypercalls
> > > now to
> > > construct an ARM guest.
> > I think it would be best to keep anything that we know can be used on
> > arm (or new architecture) in common code. I am thinking about
> > "nestedhvm" and "altp2m".
> Neither of those options are going to survive in this form.
Oh, it wasn't clear from the commit message. Would you mind to add a 
sentence in the commit message about it?
> Also, the checks can't stay in common code.  Currently, Xen doesn't
> reject bad parameters, and the toolstack doesn't check return values.
> Frankly, neither of these bugs should ever have got through code review,
> seeing as we were doing rather better code review by the time the ARM
> port came about.
The HVM_PARAM is not great on Arm :(. It would be nice to get this fixed 
properly.
> I've fixed the libxl code to check return values, but when the
> hypervisor has its
> "not-quite-an-XSA-because-the-guest-induced-damage-is-in-unsupported-subsystems"
> bugs fixed, these hypercalls will start failing.
Cheers,

--
Julien Grall

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