Re: [RFC PATCH v1 2/8] vfio-ccw: Don't inject an I/O interrupt if the subchannel is not enabled

[Eric Farman <farman@linux.ibm.com>]

On 11/18/19 1:23 PM, Cornelia Huck wrote:
> On Fri, 15 Nov 2019 04:34:31 +0100
> Eric Farman <farman@linux.ibm.com> wrote:
> 
>> From: Farhan Ali <alifm@linux.ibm.com>
>>
>> According to PoPs, when the SCHIB.PMCW bit 8 is 0 status presented by
>> the device is not made available to the program. So don't inject an
>> interrupt in the guest if the guest OS has not enabled the
>> subchannel.
> 
> Have you managed to trigger this state in real life?

No, and I have no notes on how this came to be.  I'll try running some
of the config tests with this reverted, and see if I can find any weirdness.

> 
>>
>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>> Signed-off-by: Eric Farman <farman@linux.ibm.com>
>> ---
>>
>> Notes:
>>     v0->v1: [EF]
>>      - Update commit message, as the bit in question is bit 8 not 15
>>
>>  hw/vfio/ccw.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
>> index 0919ddbeb8..0590a6f512 100644
>> --- a/hw/vfio/ccw.c
>> +++ b/hw/vfio/ccw.c
>> @@ -230,6 +230,11 @@ static void vfio_ccw_io_notifier_handler(void *opaque)
>>          return;
>>      }
>>  
>> +    /* Virtual subchannel is not enabled */
>> +    if (!(schib->pmcw.flags & PMCW_FLAGS_MASK_ENA)) {
> 
> How can that happen? We should not be able to disable the subchannel
> while it is in active use, should we? I fear I'm missing something
> here...

Me too...  Hrm...

> 
>> +        return;
>> +    }
>> +
>>      size = pread(vcdev->vdev.fd, region, vcdev->io_region_size,
>>                   vcdev->io_region_offset);
>>      if (size == -1) {
>