Re: [Xen-devel] [PATCH 3/4] VMX: Add posted interrupt supporting

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Keir Fraser wrote on 2013-04-09:
> On 09/04/2013 08:58, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx> wrote:
> 
>> If posted interrupt arrived after vmx_intr_assit() and before vmentry, then
>> the interrupt cannot be inject to guest in time.
> 
> But pending virtual interrupts are picked up during vmentry aren't they?
Yes. But in this case, the interrupt still in PIR not in vIRR, and vmentry 
cannot pick up interrupt from PIR. So we must sync PIR to vIRR before vmentry.

> So if the IPI occurs before vmentry, why is there a race? Isn't the only
> purpose of __vmx_deliver_posted_interrupt() to ensure that the pending
> virtual interrupts of the given vcpu get scanned/handled by the
> appropriate processor?
> 
>  -- Keir
>  
>> vmx_asm_do_vmentry:
>>         call vmx_intr_assist
>>         call nvmx_switch_guest
>>         ASSERT_NOT_IN_ATOMIC
>>                               <---------if posted interrupt arrived here and
>> we don't set softirq, then the interrupt will be delay until next vmentry.
>>         GET_CURRENT(%rbx)
>>         cli
>>         
>>         mov  VCPU_processor(%rbx),%eax
>>         shl  $IRQSTAT_shift,%eax
>>         lea  irq_stat+IRQSTAT_softirq_pending(%rip),%rdx
>>         cmpl $0,(%rdx,%rax,1)
>>         jnz  .Lvmx_process_softirqs
>> Actually, the posted interrupt is same with a normal vcpu kick IPI, except
>> that if cpu received it in non-root mode, it will not cause vmext. So we must
>> follow the vcpu_kick logic.
>


Best regards,
Yang



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