Re: [Xen-devel] [PATCH 12/20] xen/domctl: Merge max_vcpus into createdomain

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Mar 19, 2018 at 07:13:51PM +0000, Andrew Cooper wrote:
> XEN_DOMCTL_max_vcpus is a mandatory hypercall, but nothing actually prevents a
> toolstack from unpausing a domain with no vcpus.
> 
> Originally, d->vcpus[] was an embedded array in struct domain, but c/s
> fb442e217 "x86_64: allow more vCPU-s per guest" in Xen 4.0 altered it to being
> dynamically allocated.  A side effect of this is that d->vcpu[] is NULL until
> XEN_DOMCTL_max_vcpus has completed, but a lot of hypercalls blindly
> dereference it.
> 
> Even today, the behaviour of XEN_DOMCTL_max_vcpus is a mandatory singleton
> call which can't change the number of vcpus once a value has been chosen.
> Therefore, delete XEN_DOMCTL_max_vcpus (including XSM hooks and toolstack
> wrappers) and retain the functionality in XEN_DOMCTL_createdomain.
> 
> This will allow future cleanup to ensure that d->vcpus[] is always valid for a
> locatable domain, and allow simplification of some creation logic which needs
> to size domain-wide objects based on max_cpus, which currently have to be
> deferred until vcpu construction.
> 
> For the python stubs, extend the domain_create keyword list to take a
> max_vcpus parameter, in lieu of deleting the pyxc_domain_max_vcpus function.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>

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