Re: [Xen-devel] [PATCH v6 15/18] vmx: Properly handle notification event when vCPU is running

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

Jan Beulich wrote on 2015-09-07:
>> +     *      jnz  .Lvmx_process_softirqs
>> +     *
>> +     *      ......
>> +     *
>> +     *      je   .Lvmx_launch
>> +     *
>> +     *      ......
>> +     *
>> +     *     .Lvmx_process_softirqs:
>> +     *      sti
>> +     *      call do_softirq
>> +     *      jmp  .Lvmx_do_vmentry
>> +     *
>> +     * If VT-d engine issues a notification event at point 1 above, it 
>> cannot
>> +     * be delivered to the guest during this VM-entry without raising the
>> +     * softirq in this notification handler.
>> +     */
>> +    raise_softirq(VCPU_KICK_SOFTIRQ);
>> +
>> +    this_cpu(irq_count)++;
>> +}
>> +
>>  const struct hvm_function_table * __init start_vmx(void)
>>  {
>>      set_in_cr4(X86_CR4_VMXE);
>> @@ -2073,7 +2119,7 @@ const struct hvm_function_table * __init
>> start_vmx(void)
>> 
>>      if ( cpu_has_vmx_posted_intr_processing )
>>      {
>> -        alloc_direct_apic_vector(&posted_intr_vector,
>> event_check_interrupt); +       
>> alloc_direct_apic_vector(&posted_intr_vector,
>> pi_notification_interrupt);
>> 
>>          if ( iommu_intpost )
>>              alloc_direct_apic_vector(&pi_wakeup_vector,
> pi_wakeup_interrupt);
> 
> Considering that you do this setup independent of iommu_intpost, won't
> this (namely, but not only) for the !iommu_inpost case result in a whole
> lot of useless softirqs to be raised? IOW - shouldn't this setup be
> conditional, and shouldn't the handler also only conditionally raise the
> softirq (to as much as possible limit their amount)?
> 
> Yang, in this context: Why does __vmx_deliver_posted_interrupt()
> not use cpu_raise_softirq(), instead kind of open coding it (see your
> d7dafa375b ["VMX: Add posted interrupt supporting"])?

Sorry, I am not in the context. What do you mean of using cpu_raise_softirq() 
in __vmx_deliver_posted_interrupt()?

Best regards,
Yang


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