[PATCH RFC] vfio error recovery: kernel support

[Michael S. Tsirkin]

This is a design and an initial patch for kernel side for AER
support in VFIO.

0. What happens now (PCIE AER only)
   Fatal errors cause a link reset.
   Non fatal errors don't.
   All errors stop the VM eventually, but not immediately
   because it's detected and reported asynchronously.
   Interrupts are forwarded as usual.
   Correctable errors are not reported to guest at all.
   Note: PPC EEH is different. This focuses on AER.

1. Correctable errors
   I don't see a need to report these to guest. So let's not.

2. Fatal errors
   It's not easy to handle them gracefully since link reset
   is needed. As a first step, let's use the existing mechanism
   in that case.
   
2. Non-fatal errors
   Here we could make progress by reporting them to guest
   and have guest handle them.
   Issues:
    a. this behaviour should only be enabled with new userspace
       old userspace should work without changes
    Suggestion: One way to address this would be to add a new eventfd
    non_fatal_err_trigger. If not set, invoke err_trigger.

    b. drivers are supposed to stop MMIO when error is reported
    if vm keeps going, we will keep doing MMIO/config
    Suggestion 1: ignore this. vm stop happens much later when userspace runs anyway,
    so we are not making things much worse
    Suggestion 2: try to stop MMIO/config, resume on resume call

    Patch below implements Suggestion 1.

    c. PF driver might detect that function is completely broken,
    if vm keeps going, we will keep doing MMIO/config
    Suggestion 1: ignore this. vm stop happens much later when userspace runs anyway,
    so we are not making things much worse
    Suggestion 2: detect this and invoke err_trigger to stop VM

    Patch below implements Suggestion 2.

Aside: we currently return PCI_ERS_RESULT_DISCONNECT when device
is not attached. This seems bogus, likely based on the confusing name.
We probably should return PCI_ERS_RESULT_CAN_RECOVER.

The following patch does not change that.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

---

The patch is completely untested. Let's discuss the design first.
Cao jin, if this is deemed acceptable please take it from here.

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index dce511f..fdca683 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -1292,7 +1292,9 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
 
 	mutex_lock(&vdev->igate);
 
-	if (vdev->err_trigger)
+	if (state == pci_channel_io_normal && vdev->non_fatal_err_trigger)
+		eventfd_signal(vdev->err_trigger, 1);
+	else if (vdev->err_trigger)
 		eventfd_signal(vdev->err_trigger, 1);
 
 	mutex_unlock(&vdev->igate);
@@ -1302,8 +1304,38 @@ static pci_ers_result_t vfio_pci_aer_err_detected(struct pci_dev *pdev,
 	return PCI_ERS_RESULT_CAN_RECOVER;
 }
 
+static pci_ers_result_t vfio_pci_aer_slot_reset(struct pci_dev *pdev,
+						pci_channel_state_t state)
+{
+	struct vfio_pci_device *vdev;
+	struct vfio_device *device;
+
+	device = vfio_device_get_from_dev(&pdev->dev);
+	if (!device)
+		goto err_dev;
+
+	vdev = vfio_device_data(device);
+	if (!vdev)
+		goto err_dev;
+
+	mutex_lock(&vdev->igate);
+
+	if (vdev->err_trigger)
+		eventfd_signal(vdev->err_trigger, 1);
+
+	mutex_unlock(&vdev->igate);
+
+	vfio_device_put(device);
+
+err_data:
+	vfio_device_put(device);
+err_dev:
+	return PCI_ERS_RESULT_RECOVERED;
+}
+
 static const struct pci_error_handlers vfio_err_handlers = {
 	.error_detected = vfio_pci_aer_err_detected,
+	.slot_reset = vfio_pci_aer_slot_reset,
 };
 
 static struct pci_driver vfio_pci_driver = {
diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index 1c46045..e883db5 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -611,6 +611,17 @@ static int vfio_pci_set_err_trigger(struct vfio_pci_device *vdev,
 					       count, flags, data);
 }
 
+static int vfio_pci_set_non_fatal_err_trigger(struct vfio_pci_device *vdev,
+				    unsigned index, unsigned start,
+				    unsigned count, uint32_t flags, void *data)
+{
+	if (index != VFIO_PCI_NON_FATAL_ERR_IRQ_INDEX || start != 0 || count > 1)
+		return -EINVAL;
+
+	return vfio_pci_set_ctx_trigger_single(&vdev->non_fatal_err_trigger,
+					       count, flags, data);
+}
+
 static int vfio_pci_set_req_trigger(struct vfio_pci_device *vdev,
 				    unsigned index, unsigned start,
 				    unsigned count, uint32_t flags, void *data)
@@ -664,6 +675,14 @@ int vfio_pci_set_irqs_ioctl(struct vfio_pci_device *vdev, uint32_t flags,
 			break;
 		}
 		break;
+	case VFIO_PCI_NON_FATAL_ERR_IRQ_INDEX:
+		switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
+		case VFIO_IRQ_SET_ACTION_TRIGGER:
+			if (pci_is_pcie(vdev->pdev))
+				func = vfio_pci_set_err_trigger;
+			break;
+		}
+		break;
 	case VFIO_PCI_REQ_IRQ_INDEX:
 		switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
 		case VFIO_IRQ_SET_ACTION_TRIGGER:
diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
index f37c73b..c27a507 100644
--- a/drivers/vfio/pci/vfio_pci_private.h
+++ b/drivers/vfio/pci/vfio_pci_private.h
@@ -93,6 +93,7 @@ struct vfio_pci_device {
 	struct pci_saved_state	*pci_saved_state;
 	int			refcnt;
 	struct eventfd_ctx	*err_trigger;
+	struct eventfd_ctx	*non_fatal_err_trigger;
 	struct eventfd_ctx	*req_trigger;
 	struct list_head	dummy_resources_list;
 };

-- 
MST