Re: [Xen-devel] [PATCH 7/7] vm-event/arm: implement support for control-register write vm-events

[Julien Grall <julien.grall@xxxxxxx>]

On 22/06/2016 20:37, Corneliu ZUZU wrote:
> I've also realized that it's a bit complicated to avoid writing HCR from
> 2 places.
> That's because:
> - p2m_restore_state is part of the process of switching to another vCPU
> and the HCR write _must be committed_ here because other components
> depend on that, like address-translation functions
> - I want vm_event_vcpu_enter to be called _after_ the switch to the vCPU
> is completed
> - I want HCR_TVM to be set in vm_event_vcpu_enter because setting
> necessary traps _for cr vm-events_ to work should be done there (setting
> HCR_TVM bit makes sense to be there and the purpose is to centralize
> operations such as this for code comprehensibility; also, on the X86
> counterpart a similar operation is done for trapping CR3, so it would be
> nice to keep the symmetry)
>
> Would it be such a stretch to have HCR written in 2 places? (the second
> time happens rarely anyway: it's unlikely(..) to have to do the write in
> vm_event_vcpu_enter)
Not really. It was mostly to avoid setting/clearing HCR bits in 
different place in the code. It makes more difficult to know what is the 
final result of the register.
Anyway, let's skip it for now, if it is too difficult.

Regards,

--
Julien Grall

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