Re: [PATCH for-4.15 v2] VMX: use a single, global APIC access page [and 1 more messages]

[Ian Jackson <iwj@xxxxxxxxxxxxxx>]

Jan Beulich writes ("[PATCH v2] VMX: use a single, global APIC access page"):
> The address of this page is used by the CPU only to recognize when to
> access the virtual APIC page instead. No accesses would ever go to this
> page. It only needs to be present in the (CPU) page tables so that
> address translation will produce its address as result for respective
> accesses.
> 
> By making this page global, we also eliminate the need to refcount it,
> or to assign it to any domain in the first place.

Thanks for this.

>From this:

Jan Beulich writes ("Re: [PATCH v2] VMX: use a single, global APIC access 
page"):
> While this patch was triggered not just by Julien's observation of
> the early p2m insertion being a problem, but also many earlier
> times of running into this odd code, it is - especially at this
> stage - perhaps a possible option to split the change into just
> the movement of the set_mmio_p2m_entry() invocation and all the
> rest, in order to defer that rest until after 4.15.

I infer that this contains a bugfix, but perhaps other
changes/improvements too.

George, I think you're our expert on this refcounting stuff - what do
you think of this ?

I guess my key question is whether this change will introduce risk by
messing with the complex refcounting machineryt - or remove it by
removing an interaction with the refcounting.

Thanks,
Ian.