Re: [Qemu-devel] [Qemu-ppc] [PATCH qemu v13 07/16] vfio, memory: Notify IOMMU about starting/stopping being used by VFIO

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 03/03/2016 04:28 PM, David Gibson wrote:
> On Tue, Mar 01, 2016 at 08:10:32PM +1100, Alexey Kardashevskiy wrote:
>> This adds a vfio_votify() callback to inform an IOMMU (and then its owner)
>> that VFIO started using the IOMMU. This is used by the pseries machine to
>> enable/disable in-kernel acceleration of TCE hypercalls.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>
> Hmm.. the current approach of having a hook when vfio-pci devices are
> attached is pretty ugly, but what exactly the case that it doesn't
> handle and this approach does?

Sorry, I am not following you here. What hook do you mean here?

My hook fixes the case when I want to enable/disable KVM acceleration, 
without these patches, I need to re-count how many vfio-pci devices are 
there and it is more ugly with PCI hotplug/unplug...


> This two tiered notify system for a single bit is also kinda ugly.
>
>> ---
>>   hw/ppc/spapr_iommu.c   |  9 +++++++++
>>   hw/ppc/spapr_pci.c     | 14 ++++++++------
>>   hw/vfio/common.c       |  7 +++++++
>>   include/exec/memory.h  |  2 ++
>>   include/hw/ppc/spapr.h |  4 ++++
>>   5 files changed, 30 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
>> index 8a88a74..67a8356 100644
>> --- a/hw/ppc/spapr_iommu.c
>> +++ b/hw/ppc/spapr_iommu.c
>> @@ -136,6 +136,13 @@ static IOMMUTLBEntry spapr_tce_translate_iommu(MemoryRegion *iommu, hwaddr addr,
>>       return ret;
>>   }
>>
>> +static int spapr_tce_vfio_notify(MemoryRegion *iommu, bool attached)
>> +{
>> +    sPAPRTCETable *tcet = container_of(iommu, sPAPRTCETable, iommu);
>> +
>> +    return spapr_tce_vfio_notify_owner(tcet->owner, tcet, attached);
>
> I'm guessing the "owner" is the PHB, but I'm not entirely clear.
>
> Could you use the QOM parent to get the the PHB instead of storing it
> explicitly?


I am pretty sure I am not allowed to use the QOM parent, this is why there 
is no object_get_parent() helper.


>
>> +}
>> +
>>   static int spapr_tce_table_post_load(void *opaque, int version_id)
>>   {
>>       sPAPRTCETable *tcet = SPAPR_TCE_TABLE(opaque);
>> @@ -167,6 +174,7 @@ static const VMStateDescription vmstate_spapr_tce_table = {
>>
>>   static MemoryRegionIOMMUOps spapr_iommu_ops = {
>>       .translate = spapr_tce_translate_iommu,
>> +    .vfio_notify = spapr_tce_vfio_notify,
>>   };
>>
>>   static int spapr_tce_table_realize(DeviceState *dev)
>> @@ -235,6 +243,7 @@ sPAPRTCETable *spapr_tce_new_table(DeviceState *owner, uint32_t liobn)
>>
>>       tcet = SPAPR_TCE_TABLE(object_new(TYPE_SPAPR_TCE_TABLE));
>>       tcet->liobn = liobn;
>> +    tcet->owner = owner;
>>
>>       snprintf(tmp, sizeof(tmp), "tce-table-%x", liobn);
>>       object_property_add_child(OBJECT(owner), tmp, OBJECT(tcet), NULL);
>> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
>> index ee0fecf..b0cd148 100644
>> --- a/hw/ppc/spapr_pci.c
>> +++ b/hw/ppc/spapr_pci.c
>> @@ -1084,6 +1084,14 @@ static int spapr_populate_pci_child_dt(PCIDevice *dev, void *fdt, int offset,
>>       return 0;
>>   }
>>
>> +int spapr_tce_vfio_notify_owner(DeviceState *dev, sPAPRTCETable *tcet,
>> +                                bool attached)
>> +{
>> +    spapr_tce_set_need_vfio(tcet, attached);
>
> Hmm.. you go to the trouble of storing owner in dev, then don't
> actually use it.


Yeah, I need to clean this, I removed spapr_tce_vfio_notify_owner() from my 
working branch already and call spapr_tce_set_need_vfio() directly from 
spapr_tce_vfio_notify().


>
>> +    return 0;
>> +}
>> +
>>   /* create OF node for pci device and required OF DT properties */
>>   static int spapr_create_pci_child_dt(sPAPRPHBState *phb, PCIDevice *dev,
>>                                        void *fdt, int node_offset)
>> @@ -1118,12 +1126,6 @@ static void spapr_phb_add_pci_device(sPAPRDRConnector *drc,
>>       void *fdt = NULL;
>>       int fdt_start_offset = 0, fdt_size;
>>
>> -    if (object_dynamic_cast(OBJECT(pdev), "vfio-pci")) {
>> -        sPAPRTCETable *tcet = spapr_tce_find_by_liobn(phb->dma_liobn);
>> -
>> -        spapr_tce_set_need_vfio(tcet, true);
>> -    }
>> -
>>       if (dev->hotplugged) {
>>           fdt = create_device_tree(&fdt_size);
>>           fdt_start_offset = spapr_create_pci_child_dt(phb, pdev, fdt, 0);
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 9bf4c3b..ca3fd47 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -384,6 +384,7 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>           QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
>>
>>           memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
>> +        giommu->iommu->iommu_ops->vfio_notify(section->mr, true);
>>           memory_region_iommu_replay(giommu->iommu, &giommu->n,
>>                                      vfio_container_granularity(container),
>>                                      false);
>> @@ -430,6 +431,7 @@ static void vfio_listener_region_del(MemoryListener *listener,
>>       VFIOContainer *container = container_of(listener, VFIOContainer, listener);
>>       hwaddr iova, end;
>>       int ret;
>> +    MemoryRegion *iommu = NULL;
>>
>>       if (vfio_listener_skipped_section(section)) {
>>           trace_vfio_listener_region_del_skip(
>> @@ -451,6 +453,7 @@ static void vfio_listener_region_del(MemoryListener *listener,
>>           QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
>>               if (giommu->iommu == section->mr) {
>>                   memory_region_unregister_iommu_notifier(&giommu->n);
>> +                iommu = giommu->iommu;
>>                   QLIST_REMOVE(giommu, giommu_next);
>>                   g_free(giommu);
>>                   break;
>> @@ -483,6 +486,10 @@ static void vfio_listener_region_del(MemoryListener *listener,
>>                        "0x%"HWADDR_PRIx") = %d (%m)",
>>                        container, iova, end - iova, ret);
>>       }
>> +
>> +    if (iommu && iommu->iommu_ops && iommu->iommu_ops->vfio_notify) {
>> +        iommu->iommu_ops->vfio_notify(section->mr, false);
>> +    }
>
> So, if an IOMMU is removed from the guest, this will turn off VFIO
> enablement.  However, IIUC this won't get caled in the more likely
> case that the address space stays the same, but the VFIO device is
> removed.


When VFIO device is removed, its listener gets removed and this is supposed 
to end up calling vfio_listener_region_del().


>
>>   }
>>
>>   static const MemoryListener vfio_memory_listener = {
>> diff --git a/include/exec/memory.h b/include/exec/memory.h
>> index d5284c2..9f82629 100644
>> --- a/include/exec/memory.h
>> +++ b/include/exec/memory.h
>> @@ -150,6 +150,8 @@ typedef struct MemoryRegionIOMMUOps MemoryRegionIOMMUOps;
>>   struct MemoryRegionIOMMUOps {
>>       /* Return a TLB entry that contains a given address. */
>>       IOMMUTLBEntry (*translate)(MemoryRegion *iommu, hwaddr addr, bool is_write);
>> +    /* Called when VFIO starts/stops using this */
>> +    int (*vfio_notify)(MemoryRegion *iommu, bool attached);
>>   };
>>
>>   typedef struct CoalescedMemoryRange CoalescedMemoryRange;
>> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
>> index 8aa0c45..5d2f8f4 100644
>> --- a/include/hw/ppc/spapr.h
>> +++ b/include/hw/ppc/spapr.h
>> @@ -550,6 +550,7 @@ struct sPAPRTCETable {
>>       int fd;
>>       MemoryRegion root, iommu;
>>       struct VIOsPAPRDevice *vdev; /* for @bypass migration compatibility only */
>> +    DeviceState *owner;
>>       QLIST_ENTRY(sPAPRTCETable) list;
>>   };
>>
>> @@ -629,4 +630,7 @@ int spapr_rng_populate_dt(void *fdt);
>>    */
>>   #define SPAPR_LMB_FLAGS_ASSIGNED 0x00000008
>>
>> +int spapr_tce_vfio_notify_owner(DeviceState *dev, sPAPRTCETable *tcet,
>> +                                bool attached);
>> +
>>   #endif /* !defined (__HW_SPAPR_H__) */
>


-- 
Alexey