Re: [PATCH v3 06/11] KVM: x86: Set current_vcpu per-cpu var before enabling interrupts at host

[Liran Alon <LIRAN.ALON@ORACLE.COM>]

On 27/12/17 12:06, Paolo Bonzini wrote:
> On 24/12/2017 17:12, Liran Alon wrote:
>>
>> +	kvm_before_handle_host_interrupts(vcpu);
>>   	local_irq_enable();
>> +	kvm_after_handle_host_interrupts(vcpu);
>>   	preempt_enable();
>
> This should be around the call to kvm_x86_ops->handle_external_intr, not
> here.
>
> Also, perhaps you could: 1) do the kvm_before_handle_* unconditionally
> before the point where NMIs would be injected; 2) remove the
> kvm_after_handle_* from vmx_complete_atomic_exit and svm_vcpu_run; 3)
> only do kvm_after_handle_* after kvm_x86_ops->handle_external_intr, not
> before it.
>
> Paolo
>

The intention of this change was that later commit can handle the case 
where nested posted-interrupts processing is triggered by self-IPI but 
the CPU has immediately exited guest after resume because of another 
external interrupt (different than POSTED_INTR_NESTED_VECTOR).

In this case, the POSTED_INTR_NESTED_VECTOR interrupt will be triggered 
on host after vcpu_enter_guest() calls local_irq_enable(). And our 
handler should re-set vmx->nested.pi_pending to true so that on next 
vmentry, vmx_complete_nested_posted_interrupt() will re-trigger a self-IPI.

Therefore it is not sufficient to put calls to 
kvm_{before,after}_handle_host_interrupts around call to 
kvm_x86_ops->handle_external_intr().

But you are correct that it makes sense to also put these calls around 
that call-site as-well.

So as I see it, we have 2 alternatives here:
1. Just add calls around kvm_x86_ops->handle_external_intr().
2. Go with your suggestion but with a more intuitive approach:
Change only vcpu_enter_guest() such that:
a. Will call  kvm_before_handle_host_interrupts() after setting 
vcpu->mode = IN_GUEST_MODE.
b. Will call kvm_after_handle_host_interrupts() after calls to 
local_irq_enable() (One in case there is a pending KVM requst and one 
after guest was run and we exited guest normally).

What do you think?

Regards,
-Liran