Re: [Qemu-devel] [PATCH] spapr/xive: H_INT_ESB is used for LSIs only

[Cédric Le Goater]

On 01/07/2019 07:07, David Gibson wrote:
> On Fri, Jun 21, 2019 at 05:05:45PM +0200, Cédric Le Goater wrote:
>> On 21/06/2019 16:52, Greg Kurz wrote:
>>> As indicated in the function header, this "hcall is only supported for
>>> LISNs that have the ESB hcall flag set to 1 when returned from hcall()
>>> H_INT_GET_SOURCE_INFO". We only set that flag for LSIs actually.
>>>
>>> Check that in h_int_esb().
>>
>> Indeed. H_INT_ESB should work on any IRQ, but I think it's better 
>> to check that the HCALL is only used with the IRQ requiring it.
> 
> I'm not so convinced.  It seems to me that specifically limiting this
> to certain things limits our options if we ever need future
> workarounds for problems with ESB mapping.
> 
> In addition using H_INT_ESB for non-LSIs could be useful for minimal
> guests (e.g. kvm-unit-tests) where mapping memory might be awkward.

Ah yes. This is true. There is no real reason for enforcing this
restriction in QEMU as H_INT_ESB should work on any irq. We can
keep it that way I guess. It would be a small deviation from PAPR.

Thanks,

C. 

> So, I'm not really seeing a compelling reason to apply this.
> 
>>
>>> Signed-off-by: Greg Kurz <address@hidden>
>>
>> Reviewed-by: Cédric Le Goater <address@hidden>
>>
>> Thanks,
>>
>> C.
>>
>>> ---
>>>  hw/intc/spapr_xive.c |    6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/hw/intc/spapr_xive.c b/hw/intc/spapr_xive.c
>>> index 58c2e5d890bd..01dd47ad5b02 100644
>>> --- a/hw/intc/spapr_xive.c
>>> +++ b/hw/intc/spapr_xive.c
>>> @@ -1408,6 +1408,12 @@ static target_ulong h_int_esb(PowerPCCPU *cpu,
>>>          return H_P2;
>>>      }
>>>  
>>> +    if (!xive_source_irq_is_lsi(xsrc, lisn)) {
>>> +        qemu_log_mask(LOG_GUEST_ERROR, "XIVE: LISN " TARGET_FMT_lx "isn't 
>>> LSI\n",
>>> +                      lisn);
>>> +        return H_P2;
>>> +    }
>>> +
>>>      if (offset > (1ull << xsrc->esb_shift)) {
>>>          return H_P3;
>>>      }
>>>
>>
>