Re: [PATCH V8 28/39] vfio-pci: cpr part 2 (msi)

[Alex Williamson]

On Wed, 15 Jun 2022 07:52:15 -0700
Steve Sistare <steven.sistare@oracle.com> wrote:

> Finish cpr for vfio-pci MSI/MSI-X devices by preserving eventfd's and
> vector state.
> 
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  hw/vfio/pci.c | 122 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 121 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 237231b..2fd7121 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -53,17 +53,53 @@ static void vfio_disable_interrupts(VFIOPCIDevice *vdev);
>  static void vfio_mmap_set_enabled(VFIOPCIDevice *vdev, bool enabled);
>  static void vfio_msi_disable_common(VFIOPCIDevice *vdev);
>  
> +#define EVENT_FD_NAME(vdev, name)   \
> +    g_strdup_printf("%s_%s", (vdev)->vbasedev.name, (name))
> +
> +static int save_event_fd(VFIOPCIDevice *vdev, const char *name, int nr,
> +                         EventNotifier *ev)
> +{
> +    int fd = event_notifier_get_fd(ev);
> +
> +    if (fd >= 0) {
> +        Error *err;
> +        g_autofree char *fdname = EVENT_FD_NAME(vdev, name);
> +
> +        if (cpr_resave_fd(fdname, nr, fd, &err)) {
> +            error_report_err(err);
> +            return 1;


Preferably -1, but the caller doesn't actually test the return value
anyway :-\


> +        }
> +    }
> +    return 0;
> +}
> +
> +static int load_event_fd(VFIOPCIDevice *vdev, const char *name, int nr)
> +{
> +    g_autofree char *fdname = EVENT_FD_NAME(vdev, name);
> +    int fd = cpr_find_fd(fdname, nr);
> +    return fd;


    return cpr_find_fd(EVENT_FD_NAME(vdev, name), nr);


> +}
> +
> +static void delete_event_fd(VFIOPCIDevice *vdev, const char *name, int nr)
> +{
> +    g_autofree char *fdname = EVENT_FD_NAME(vdev, name);
> +    cpr_delete_fd(fdname, nr);


    cpr_delete_fd(EVENT_FD_NAME(vdev, name), nr);


> +}
> +
>  /* Create new or reuse existing eventfd */
>  static int vfio_notifier_init(VFIOPCIDevice *vdev, EventNotifier *e,
>                                const char *name, int nr)
>  {
> -    int fd = -1;   /* placeholder until a subsequent patch */
>      int ret = 0;
> +    int fd = load_event_fd(vdev, name, nr);
>  
>      if (fd >= 0) {
>          event_notifier_init_fd(e, fd);
>      } else {
>          ret = event_notifier_init(e, 0);
> +        if (!ret) {
> +            save_event_fd(vdev, name, nr, e);


Return value not tested.  The function generates an error report if it
fails, but it doesn't seem that actually blocks a cpr attempt.  Do we
just wind up with that error report as a breadcrumb to why cpr breaks
with a missing fd down the road?


> +        }
>      }
>      return ret;
>  }
> @@ -71,6 +107,7 @@ static int vfio_notifier_init(VFIOPCIDevice *vdev, 
> EventNotifier *e,
>  static void vfio_notifier_cleanup(VFIOPCIDevice *vdev, EventNotifier *e,
>                                    const char *name, int nr)
>  {
> +    delete_event_fd(vdev, name, nr);
>      event_notifier_cleanup(e);
>  }
>  
> @@ -511,6 +548,15 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, 
> unsigned int nr,
>      VFIOMSIVector *vector;
>      int ret;
>  
> +    /*
> +     * Ignore the callback from msix_set_vector_notifiers during resume.
> +     * The necessary subset of these actions is called from 
> vfio_claim_vectors
> +     * during post load.
> +     */
> +    if (vdev->vbasedev.reused) {
> +        return 0;
> +    }
> +
>      trace_vfio_msix_vector_do_use(vdev->vbasedev.name, nr);
>  
>      vector = &vdev->msi_vectors[nr];
> @@ -2784,6 +2830,11 @@ static void vfio_register_err_notifier(VFIOPCIDevice 
> *vdev)
>      fd = event_notifier_get_fd(&vdev->err_notifier);
>      qemu_set_fd_handler(fd, vfio_err_notifier_handler, NULL, vdev);
>  
> +    /* Do not alter irq_signaling during vfio_realize for cpr */
> +    if (vdev->vbasedev.reused) {
> +        return;
> +    }
> +
>      if (vfio_set_irq_signaling(&vdev->vbasedev, VFIO_PCI_ERR_IRQ_INDEX, 0,
>                                 VFIO_IRQ_SET_ACTION_TRIGGER, fd, &err)) {
>          error_reportf_err(err, VFIO_MSG_PREFIX, vdev->vbasedev.name);
> @@ -2849,6 +2900,12 @@ static void vfio_register_req_notifier(VFIOPCIDevice 
> *vdev)
>      fd = event_notifier_get_fd(&vdev->req_notifier);
>      qemu_set_fd_handler(fd, vfio_req_notifier_handler, NULL, vdev);
>  
> +    /* Do not alter irq_signaling during vfio_realize for cpr */
> +    if (vdev->vbasedev.reused) {
> +        vdev->req_enabled = true;
> +        return;
> +    }


vfio_notifier_init() transparently gets the old fd or creates a new
one, how do we know which has occurred to know that this eventfd is
already configured?

Don't we also have the same issue relative to vdev->pci_aer for the
error handler?

> +
>      if (vfio_set_irq_signaling(&vdev->vbasedev, VFIO_PCI_REQ_IRQ_INDEX, 0,
>                             VFIO_IRQ_SET_ACTION_TRIGGER, fd, &err)) {
>          error_reportf_err(err, VFIO_MSG_PREFIX, vdev->vbasedev.name);
> @@ -3357,6 +3414,43 @@ static Property vfio_pci_dev_properties[] = {
>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> +static void vfio_claim_vectors(VFIOPCIDevice *vdev, int nr_vectors, bool 
> msix)
> +{
> +    int i, fd;
> +    bool pending = false;
> +    PCIDevice *pdev = &vdev->pdev;
> +
> +    vdev->nr_vectors = nr_vectors;
> +    vdev->msi_vectors = g_new0(VFIOMSIVector, nr_vectors);
> +    vdev->interrupt = msix ? VFIO_INT_MSIX : VFIO_INT_MSI;
> +
> +    for (i = 0; i < nr_vectors; i++) {
> +        VFIOMSIVector *vector = &vdev->msi_vectors[i];
> +
> +        fd = load_event_fd(vdev, "interrupt", i);
> +        if (fd >= 0) {
> +            vfio_vector_init(vdev, i);
> +            qemu_set_fd_handler(fd, vfio_msi_interrupt, NULL, vector);
> +        }
> +
> +        if (load_event_fd(vdev, "kvm_interrupt", i) >= 0) {
> +            vfio_route_change = kvm_irqchip_begin_route_changes(kvm_state);
> +            vfio_add_kvm_msi_virq(vdev, vector, i, msix);
> +            kvm_irqchip_commit_route_changes(&vfio_route_change);
> +            vfio_connect_kvm_msi_virq(vector, i);


Shouldn't we take advantage of the batching support here?


> +        }


How do we debug if one of the above fails that shouldn't have failed?
Should we have an assert or change this to a non-void return if we
cannot setup an interrupt that we think is configured?


> +
> +        if (msix && msix_is_pending(pdev, i) && msix_is_masked(pdev, i)) {
> +            set_bit(i, vdev->msix->pending);
> +            pending = true;
> +        }
> +    }
> +
> +    if (msix) {
> +        memory_region_set_enabled(&pdev->msix_pba_mmio, pending);
> +    }
> +}
> +
>  /*
>   * The kernel may change non-emulated config bits.  Exclude them from the
>   * changed-bits check in get_pci_config_device.
> @@ -3375,6 +3469,29 @@ static int vfio_pci_pre_load(void *opaque)
>      return 0;
>  }
>  
> +static int vfio_pci_post_load(void *opaque, int version_id)
> +{
> +    VFIOPCIDevice *vdev = opaque;
> +    PCIDevice *pdev = &vdev->pdev;
> +    int nr_vectors;
> +
> +    if (msix_enabled(pdev)) {
> +        msix_set_vector_notifiers(pdev, vfio_msix_vector_use,
> +                                   vfio_msix_vector_release, NULL);
> +        nr_vectors = vdev->msix->entries;



Maybe this is why we're not generating an error above, we don't know
which vectors are configured other than if they have a saved eventfd,
where we don't test whether we were able to actually save the fd.
Thanks,

Alex


> +        vfio_claim_vectors(vdev, nr_vectors, true);
> +
> +    } else if (msi_enabled(pdev)) {
> +        nr_vectors = msi_nr_vectors_allocated(pdev);
> +        vfio_claim_vectors(vdev, nr_vectors, false);
> +
> +    } else if (vfio_pci_read_config(pdev, PCI_INTERRUPT_PIN, 1)) {
> +        assert(0);      /* completed in a subsequent patch */
> +    }
> +
> +    return 0;
> +}
> +
>  static bool vfio_pci_needed(void *opaque)
>  {
>      return cpr_get_mode() == CPR_MODE_RESTART;
> @@ -3387,8 +3504,11 @@ static const VMStateDescription vfio_pci_vmstate = {
>      .minimum_version_id = 0,
>      .priority = MIG_PRI_VFIO_PCI,       /* must load before container */
>      .pre_load = vfio_pci_pre_load,
> +    .post_load = vfio_pci_post_load,
>      .needed = vfio_pci_needed,
>      .fields = (VMStateField[]) {
> +        VMSTATE_PCI_DEVICE(pdev, VFIOPCIDevice),
> +        VMSTATE_MSIX_TEST(pdev, VFIOPCIDevice, vfio_msix_present),
>          VMSTATE_END_OF_LIST()
>      }
>  };