Re: [Qemu-devel] [PATCH v3 07/12] vfio/pci: register sva notifier

[Peter Xu]

On Thu, Mar 08, 2018 at 11:22:26AM +0000, Liu, Yi L wrote:
> > From: Peter Xu [mailto:address@hidden
> > Sent: Tuesday, March 6, 2018 8:10 PM
> > To: Liu, Yi L <address@hidden>
> > Cc: Liu, Yi L <address@hidden>; address@hidden; address@hidden;
> > address@hidden; address@hidden; address@hidden;
> > address@hidden; Tian, Kevin <address@hidden>;
> > address@hidden
> > Subject: Re: [PATCH v3 07/12] vfio/pci: register sva notifier
> > 
> > On Tue, Mar 06, 2018 at 08:00:41AM +0000, Liu, Yi L wrote:
> > > > From: Peter Xu [mailto:address@hidden
> > > > Sent: Tuesday, March 6, 2018 2:45 PM
> > > > Subject: Re: [PATCH v3 07/12] vfio/pci: register sva notifier
> > > >
> > > > On Thu, Mar 01, 2018 at 06:33:30PM +0800, Liu, Yi L wrote:
> > > > > This patch shows how sva notifier is registered. And provided an
> > > > > example by registering notify func for tlb flush propagation.
> > > > >
> > > > > Signed-off-by: Liu, Yi L <address@hidden>
> > > > > ---
> > > > >  hw/vfio/pci.c | 55
> > > > > +++++++++++++++++++++++++++++++++++++++++++++++++++++--
> > > > >  1 file changed, 53 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index a60a4d7..b7297cc
> > > > > 100644
> > > > > --- a/hw/vfio/pci.c
> > > > > +++ b/hw/vfio/pci.c
> > > > > @@ -2775,6 +2775,26 @@ static void
> > > > > vfio_unregister_req_notifier(VFIOPCIDevice
> > > > *vdev)
> > > > >      vdev->req_enabled = false;
> > > > >  }
> > > > >
> > > > > +static VFIOContainer *vfio_get_container_from_busdev(PCIBus *bus,
> > > > > +                                                     int32_t devfn) {
> > > > > +    VFIOGroup *group;
> > > > > +    VFIOPCIDevice *vdev_iter;
> > > > > +    VFIODevice *vbasedev_iter;
> > > > > +    PCIDevice *pdev_iter;
> > > > > +
> > > > > +    QLIST_FOREACH(group, &vfio_group_list, next) {
> > > > > +        QLIST_FOREACH(vbasedev_iter, &group->device_list, next) {
> > > > > +            vdev_iter = container_of(vbasedev_iter, VFIOPCIDevice, 
> > > > > vbasedev);
> > > > > +            pdev_iter = &vdev_iter->pdev;
> > > > > +            if (pci_get_bus(pdev_iter) == bus && pdev_iter->devfn == 
> > > > > devfn) {
> > > > > +                return group->container;
> > > > > +            }
> > > > > +        }
> > > > > +    }
> > > > > +    return NULL;
> > > > > +}
> > > > > +
> > > > >  static void vfio_pci_device_sva_bind_pasid_table(PCIBus *bus,
> > > > >                   int32_t devfn, uint64_t pasidt_addr, uint32_t
> > > > > size) { @@ -2783,11 +2803,42 @@ static void
> > > > > vfio_pci_device_sva_bind_pasid_table(PCIBus *bus,
> > > > >      So far, Intel VT-d and AMD IOMMU requires it. */  }
> > > > >
> > > > > +static void vfio_iommu_sva_tlb_invalidate_notify(IOMMUSVANotifier *n,
> > > > > +
> > > > > +IOMMUSVAEventData
> > > > > +*event_data) {
> > > > > +/*  Sample code, would be detailed in coming virt-SVA patchset.
> > > > > +    VFIOGuestIOMMUSVAContext *gsva_ctx;
> > > > > +    IOMMUSVAContext *sva_ctx;
> > > > > +    VFIOContainer *container;
> > > > > +
> > > > > +    gsva_ctx = container_of(n, VFIOGuestIOMMUSVAContext, n);
> > > > > +    container = gsva_ctx->container;
> > > > > +
> > > > > +    TODO: forward to host through VFIO IOCTL
> > > >
> > > > IMHO if the series is not ready for merging, we can still mark it as
> > > > RFC and declare that so people won't need to go into details of the 
> > > > patches.
> > >
> > > Thanks for the suggestion. Actually, I was hesitating it. As you may
> > > know, this is actually 3rd version of this effort. But yes, I would 
> > > follow your
> > suggestion in coming versions.
> > 
> > Yeah, it's a long way even since the first version of the work.
> > However IMHO it's not about which version are you working with, it's about 
> > whether
> > you think it's a complete work and ready to be merged.
> > IMHO if you are very sure it's not good for merging, we should better 
> > provide the
> > RFC tag, or mention that in the cover letter.  So firstly the maintainer 
> > won't
> > accidentaly merge your series; meanwhile reviewers will know the state of 
> > series so
> > they can decide on which aspect they'll focus on during the review.
> 
> thanks for the guiding~
> 
> > >
> > > > > +*/
> > > > > +}
> > > > > +
> > > > >  static void vfio_pci_device_sva_register_notifier(PCIBus *bus,
> > > > >                            int32_t devfn, IOMMUSVAContext *sva_ctx)  {
> > > > > -    /* Register notifier for TLB invalidation propagation
> > > > > -       */
> > > > > +    VFIOContainer *container =
> > > > > + vfio_get_container_from_busdev(bus,
> > > > > + devfn);
> > > > > +
> > > > > +    if (container != NULL) {
> > > > > +        VFIOGuestIOMMUSVAContext *gsva_ctx;
> > > > > +        gsva_ctx = g_malloc0(sizeof(*gsva_ctx));
> > > > > +        gsva_ctx->sva_ctx = sva_ctx;
> > > > > +        gsva_ctx->container = container;
> > > > > +        QLIST_INSERT_HEAD(&container->gsva_ctx_list,
> > > > > +                          gsva_ctx,
> > > > > +                          gsva_ctx_next);
> > > > > +       /* Register vfio_iommu_sva_tlb_invalidate_notify with event 
> > > > > flag
> > > > > +           IOMMU_SVA_EVENT_TLB_INV */
> > > > > +        iommu_sva_notifier_register(sva_ctx,
> > > > > +                                    &gsva_ctx->n,
> > > > > +                                    
> > > > > vfio_iommu_sva_tlb_invalidate_notify,
> > > > > +                                    IOMMU_SVA_EVENT_TLB_INV);
> > > >
> > > > I would squash this patch into previous one since basically this is
> > > > only part of the implementation to provide vfio-speicific register hook.
> > >
> > > sure.
> > >
> > > > But a more important question is... why this?
> > > >
> > > > IMHO the notifier registration can be general for PCI.  Why vfio
> > > > needs to provide it's own register callback?  Would it be enough if it 
> > > > only
> > provides its own notify callback?
> > >
> > > The notifiers are in VFIO. However, the registration is controlled by 
> > > vIOMMU
> > emulator.
> > > In this series, PASID tagged Address Space is introduced. And the new
> > > notifiers are for such Address Space. Such Address Space is created and 
> > > deleted in
> > vIOMMU emulator.
> > > So the notifier registration needs to happen accordingly.
> > >
> > > e.g. guest SVM application bind a device to a process, it programs the
> > > guest iommu translation structure, vIOMMU emulator captures the
> > > change, and create a PASID tagged Address Space for it and register 
> > > notifiers.
> > >
> > > That's why I do it in such a manner.
> > 
> > I agree that the things are mostly managed by vIOMMU, but I still cannot 
> > understand
> > why vfio must have its own register hook.
> > 
> > Let me try to explain a bit more on my question.  Basically I was asking 
> > about
> > whether we can removet the register/unregister hook in the SVAOps, instead 
> > we can
> > have something like (I'll start to use pasid as prefix):
> > 
> > struct PCIPASIDOps {
> >     void (*pasid_bind_table)(PCIBus *bus, int32_t devfn, ...);
> >     void (*pasid_invalidate_extend_iotlb)(PCIBus *bus, int32_t devfn, ...) 
> > };
> > 
> > Firstly we keep the bind_table operation, but instead of the reg/unreg we 
> > only
> > provide a hook that device can override to listen to extend iotlb 
> > invalidations.
> 
> Yeah, I also considered do invalidation this manner. I turned to the one in 
> this patch.
> Reason as below:
>     the invalidate operation is supposed to pass down thru vfio container 
> IOCTL, for
>     each pasid_invalidate_extend_iotlb() calling, it needs to figure out a 
> vfio container,
>     which may be time consuming. Pls refer to 
> vfio_get_container_from_busdev() in this
>     patch. If we expose register/unregister hook, searching container will 
> happen only in
>     the register/unregister phase. And future invalidation could only be 
> notifier firing.
> With the reason above, I chose the register/unregister hook solution. If 
> there is solution
> to save the container searching, it would be better to do it in your 
> proposal. Pls feel free
> to let me know if any idea from you.

If there is PCIBus* and devfn passed into
pasid_invalidate_extend_iotlb() (let's assume it's called this way),
then IMHO we can get the PCIDevice*, which can be upcast to a
VFIOPCIDevice, then would VFIOPCIDevice.vbasedev.group->container be
the container for that device?

> 
> > IMHO my understanding is that the vIOMMU should be able to even hide the 
> > detailed
> > PASID information here, and only call the
> > pasid_invalidate_extend_iotlb() if the device gets extended-iotlb 
> > invalidations (then
> > it passes it down to host IOMMU, with the same information like domain ID, 
> > PASID,
> > granularity).
> > 
> > Would that work?
> 
> address, size, PASID, granularity may be enough. DID should be in host.

Yeah, it is.

Thanks,

-- 
Peter Xu