Re: [Xen-devel] [PATCH V6 08/10] xen: Add arch_domain_preinit to initialise vGIC before evtchn_init

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-06-11 at 17:20 +0800, Chen Baozi wrote:
> On Fri, Jun 05, 2015 at 05:22:56PM +0100, Ian Campbell wrote:
> > On Mon, 2015-06-01 at 20:56 +0800, Chen Baozi wrote:
> > > From: Chen Baozi <baozich@xxxxxxxxx>
> > > 
> > > evtchn_init will call domain_max_vcpus to allocate poll_mask. On
> > > arm/arm64 platform, this number is determined by the vGIC the guest
> > > is going to use, which won't be initialised until arch_domain_create
> > > is called in current implementation. However, moving arch_domain_create
> > > means that we will allocate memory before checking the XSM policy,
> > > which seems not to be acceptable because if the domain is not allowed
> > > to boot by XSM policy the expensive execution of arch_domain_create
> > > is wasteful. Thus, we create the arch_domain_preinit to make vgic_ops
> > > initialisation be done earlier.
> > 
> > I don't have a fundamental objection to this refactoring, but I'm
> > curious under what circumstances something would belong in preinit
> > rather than create, i.e. what is the expected semantics of this new hook
> > vs the old one.
> 
> Hmmm, I didn't think about it at this level, :P. Instead, I just brought
> the code which must be executed before evtchn_init in advance without
> further consideration on semantics etc...
> 
> In fact, the current arch_domain_preinit on arm is all about vgic. I
> was about to use the name vgic_preinit, but that would be an arm-specific
> name which I thought was not suitable to add in the common codes...
> 
> Or will it be clearer to call a subfunction called vgic_preinit in the
> arch_domain_preinit (for arm) and put the current main contents of
> arch_domain_preinit to vgic_preinit?

The main question which needs answering is: given some new bit of
functionality which needs initialising when should it be done in preinit
and when should it be in init?

Ian.



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