Re: [Qemu-devel] [qemu-s390x] [PATCH v3 3/5] s390: vfio_pci: Use a PCI Group structure

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 9/9/19 1:18 AM, Thomas Huth wrote:
> On 07/09/2019 02.16, Matthew Rosato wrote:
>> From: Pierre Morel <pmorel@linux.ibm.com>
>>
>> We use a S390PCIGroup structure to hold the information
>> related to zPCI Function group.
>>
>> This allows us to be ready to support multiple groups and to retrieve
>> the group information from the host.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> ---
>>  hw/s390x/s390-pci-bus.c  | 42 ++++++++++++++++++++++++++++++++++++++++++
>>  hw/s390x/s390-pci-bus.h  | 11 ++++++++++-
>>  hw/s390x/s390-pci-inst.c | 22 +++++++++++++---------
>>  3 files changed, 65 insertions(+), 10 deletions(-)
>>
>> diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
>> index 963a41c..e625217 100644
>> --- a/hw/s390x/s390-pci-bus.c
>> +++ b/hw/s390x/s390-pci-bus.c
>> @@ -730,6 +730,46 @@ static void s390_pci_iommu_free(S390pciState *s, PCIBus *bus, int32_t devfn)
>>      object_unref(OBJECT(iommu));
>>  }
>>  
>> +static S390PCIGroup *s390_grp_create(int ug)
>> +{
>> +    S390PCIGroup *grp;
>> +    S390pciState *s = s390_get_phb();
>> +
>> +    grp = g_new0(S390PCIGroup, 1);
>> +    grp->ug = ug;
>> +    QTAILQ_INSERT_TAIL(&s->zpci_grps, grp, link);
>> +    return grp;
>> +}
> 
> Maybe an ignorant question, but shouldn't there also be some kind of
> clean up function that also frees the memory again, e.g. during a
> machine reset? Or are these groups supposed to survive a machine reset?

Hmm..  Well, I think it is in line with the way the devices themselves
are handled during reset (they are not removed during a reset unless
there was a pending unplug and their info persists).  But you have a
point in that it seems sketchy to leave the group information around,
particularly in cases where the last device associated with the group
has been unplugged.

So yes, I think there is some work to be done here.  I need to
investigate whether a precautionary wiping of the list (minus the
default group) at machine reset is really good enough or whether we need
to remove group info sooner (device unplug).

Thanks,
Matt