Re: [Xen-devel] [PATCH v7 23/32] xen/x86: make sure the HVM callback vector is correctly set

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 14/10/15 16:54, Jan Beulich wrote:
>>>> On 02.10.15 at 17:48, <roger.pau@xxxxxxxxxx> wrote:
>> --- a/xen/arch/x86/hvm/irq.c
>> +++ b/xen/arch/x86/hvm/irq.c
>> @@ -330,6 +330,10 @@ void hvm_set_callback_via(struct domain *d, uint64_t 
>> via)
>>           (via_type > HVMIRQ_callback_vector) )
>>          via_type = HVMIRQ_callback_none;
>>  
>> +    if ( via_type != HVMIRQ_callback_vector &&
>> +         (!has_vlapic(d) || !has_vioapic(d) || !has_vpic(d)) )
>> +        return;
> Why are both IO-APIC and PIC required? Doesn't one suffice, or
> can't MSI-like interrupts even get delivered without either?

In real hardware, MSI-like interrupts have no interaction with the
IO-APIC or PIC.

In fact, the purpose of the IO-APIC is to turn legacy line interrupts
into MSI interrupts.  The PICs were from the pre-MSI days where it
asserted the #INTR pin on the processor.

Our virtual interrupt infrastructure should behave in a consistent manor.

~Andrew

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