Re: [Qemu-devel] [PATCH 12/13] spapr/xics: ignore the lower 4K in the IRQ number space

["Cédric Le Goater" <clg@kaod.org>]

On 2/12/19 2:06 AM, David Gibson wrote:
> On Mon, Jan 07, 2019 at 07:39:45PM +0100, Cédric Le Goater wrote:
>> The IRQ number space of the XIVE and XICS interrupt mode are aligned
>> when using the dual interrupt mode for the machine. This means that
>> the ICS offset is set to zero in QEMU and that the KVM XICS device
>> should be informed of this new value. Unfortunately, there is now way
>> to do so and KVM still maintains the XICS_IRQ_BASE (0x1000) offset.
>>
>> Ignore the lower 4K which are not used under the XICS interrupt
>> mode. These IRQ numbers are only claimed by XIVE for the CPU IPIs.
>>
>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
>> ---
>>  hw/intc/xics_kvm.c | 18 ++++++++++++++++++
>>  1 file changed, 18 insertions(+)
>>
>> diff --git a/hw/intc/xics_kvm.c b/hw/intc/xics_kvm.c
>> index 651bbfdf6966..1d21ff217b82 100644
>> --- a/hw/intc/xics_kvm.c
>> +++ b/hw/intc/xics_kvm.c
>> @@ -238,6 +238,15 @@ static void ics_get_kvm_state(ICSState *ics)
>>      for (i = 0; i < ics->nr_irqs; i++) {
>>          ICSIRQState *irq = &ics->irqs[i];
>>  
>> +        /*
>> +         * The KVM XICS device considers that the IRQ numbers should
>> +         * start at XICS_IRQ_BASE (0x1000). Ignore the lower 4K
>> +         * numbers (only claimed by XIVE for the CPU IPIs).
>> +         */
>> +        if (i + ics->offset < XICS_IRQ_BASE) {
>> +            continue;
>> +        }
>> +
> 
> This seems bogus to me.  The guest-visible irq numbers need to line up
> between xics and xive mode, yes, but that doesn't mean we need to keep
> around a great big array of unused array of ICS irq states, even in
> TCG mode.

This is because the qirqs[] array is under the machine and shared between 
both interrupt modes, xics and xive.

C.

> 
>>          kvm_device_access(kernel_xics_fd, KVM_DEV_XICS_GRP_SOURCES,
>>                            i + ics->offset, &state, false, &error_fatal);
>>  
>> @@ -303,6 +312,15 @@ static int ics_set_kvm_state(ICSState *ics, int version_id)
>>          ICSIRQState *irq = &ics->irqs[i];
>>          int ret;
>>  
>> +        /*
>> +         * The KVM XICS device considers that the IRQ numbers should
>> +         * start at XICS_IRQ_BASE (0x1000). Ignore the lower 4K
>> +         * numbers (only claimed by XIVE for the CPU IPIs).
>> +         */
>> +        if (i + ics->offset < XICS_IRQ_BASE) {
>> +            continue;
>> +        }
>> +
>>          state = irq->server;
>>          state |= (uint64_t)(irq->saved_priority & KVM_XICS_PRIORITY_MASK)
>>              << KVM_XICS_PRIORITY_SHIFT;
>