Re: [Qemu-devel] [PATCH 2/3] virtio-pci: add an option to bypass guest_notifier_mask

[Didier Pallard]

On 12/07/2015 02:59 PM, Marc-André Lureau wrote:
Hi
On Mon, Dec 7, 2015 at 2:37 PM, Marc-André Lureau
<marcandre.lur...@gmail.com> wrote:
Hi

On Thu, Dec 3, 2015 at 10:53 AM, Didier Pallard
<didier.pall...@6wind.com> wrote:
Using guest_notifier_mask function in vhost-user case may
break interrupt mask paradigm, because mask/unmask is not
really done when returning from guest_notifier_mask call, instead
message is posted in a unix socket, and processed later.

Add an option bit to disable the use of guest_notifier_mask
in virtio pci.
Why not disabling it whenever vhost-user is used if it's broken and
inefficient to be fixed?
Sorry, I missed the following patch.

I am not sure it's necessary to have a user-visible property,
especially if it's overwritten later. But apparently, other properties
are already forced.

looks good overall to me, but maintainers might have different opinions.

Signed-off-by: Didier Pallard <didier.pall...@6wind.com>
Reviewed-by: Thibaut Collet <thibaut.col...@6wind.com>
---
  hw/virtio/virtio-pci.c | 29 +++++++++++++++++++++++------
  hw/virtio/virtio-pci.h |  6 ++++++
  2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index dd48562..26bb617 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -806,7 +806,8 @@ static int kvm_virtio_pci_vector_use(VirtIOPCIProxy *proxy, 
int nvqs)
          /* If guest supports masking, set up irqfd now.
           * Otherwise, delay until unmasked in the frontend.
           */
-        if (k->guest_notifier_mask) {
+        if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
+            k->guest_notifier_mask) {
              ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
              if (ret < 0) {
                  kvm_virtio_pci_vq_vector_release(proxy, vector);
@@ -822,7 +823,8 @@ undo:
          if (vector >= msix_nr_vectors_allocated(dev)) {
              continue;
          }
-        if (k->guest_notifier_mask) {
+        if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
+            k->guest_notifier_mask) {
              kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
          }
          kvm_virtio_pci_vq_vector_release(proxy, vector);
@@ -849,7 +851,8 @@ static void kvm_virtio_pci_vector_release(VirtIOPCIProxy 
*proxy, int nvqs)
          /* If guest supports masking, clean up irqfd now.
           * Otherwise, it was cleaned when masked in the frontend.
           */
-        if (k->guest_notifier_mask) {
+        if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
+            k->guest_notifier_mask) {
              kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
          }
          kvm_virtio_pci_vq_vector_release(proxy, vector);
@@ -882,7 +885,8 @@ static int virtio_pci_vq_vector_unmask(VirtIOPCIProxy 
*proxy,
      /* If guest supports masking, irqfd is already setup, unmask it.
       * Otherwise, set it up now.
       */
-    if (k->guest_notifier_mask) {
+    if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
+        k->guest_notifier_mask) {
          k->guest_notifier_mask(vdev, queue_no, false);
          /* Test after unmasking to avoid losing events. */
          if (k->guest_notifier_pending &&
@@ -905,7 +909,8 @@ static void virtio_pci_vq_vector_mask(VirtIOPCIProxy *proxy,
      /* If guest supports masking, keep irqfd but mask it.
       * Otherwise, clean it up now.
       */
-    if (k->guest_notifier_mask) {
+    if ((proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
+        k->guest_notifier_mask) {
          k->guest_notifier_mask(vdev, queue_no, true);
      } else {
          kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
@@ -1022,7 +1027,9 @@ static int virtio_pci_set_guest_notifier(DeviceState *d, 
int n, bool assign,
          event_notifier_cleanup(notifier);
      }

-    if (!msix_enabled(&proxy->pci_dev) && vdc->guest_notifier_mask) {
+    if (!msix_enabled(&proxy->pci_dev) &&
+        (proxy->flags & VIRTIO_PCI_FLAG_USE_NOTIFIERMASK) &&
+        vdc->guest_notifier_mask) {
          vdc->guest_notifier_mask(vdev, n, !assign);
      }

@@ -1164,6 +1171,8 @@ static void virtio_9p_pci_realize(VirtIOPCIProxy 
*vpci_dev, Error **errp)
  static Property virtio_9p_pci_properties[] = {
      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
+    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
      DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
      DEFINE_PROP_END_OF_LIST(),
  };
@@ -1908,6 +1917,8 @@ static Property virtio_blk_pci_properties[] = {
      DEFINE_PROP_UINT32("class", VirtIOPCIProxy, class_code, 0),
      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
+    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
      DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
      DEFINE_PROP_END_OF_LIST(),
  };
@@ -1961,6 +1972,8 @@ static const TypeInfo virtio_blk_pci_info = {
  static Property virtio_scsi_pci_properties[] = {
      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
+    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
      DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors,
                         DEV_NVECTORS_UNSPECIFIED),
      DEFINE_PROP_END_OF_LIST(),
@@ -2175,6 +2188,8 @@ static void virtio_serial_pci_realize(VirtIOPCIProxy 
*vpci_dev, Error **errp)
  static Property virtio_serial_pci_properties[] = {
      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, true),
+    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
      DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 2),
      DEFINE_PROP_UINT32("class", VirtIOPCIProxy, class_code, 0),
      DEFINE_PROP_END_OF_LIST(),
@@ -2215,6 +2230,8 @@ static const TypeInfo virtio_serial_pci_info = {
  static Property virtio_net_properties[] = {
      DEFINE_PROP_BIT("ioeventfd", VirtIOPCIProxy, flags,
                      VIRTIO_PCI_FLAG_USE_IOEVENTFD_BIT, false),
+    DEFINE_PROP_BIT("usenotifiermask", VirtIOPCIProxy, flags,
+                    VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT, true),
      DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
      DEFINE_PROP_END_OF_LIST(),
  };
diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index ffb74bb..aecd4eb 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -86,6 +86,12 @@ typedef struct VirtioBusClass VirtioPCIBusClass;
  #define VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY \
      (1 << VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY_BIT)

+/* Where vhost-user implementation exists, using the guest notifier mask
+ * feature can lead to improper interrupt management. Add a flag to
+ * allow to disable this guest notifier mask if desired */
+#define VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT 6
+#define VIRTIO_PCI_FLAG_USE_NOTIFIERMASK (1 << 
VIRTIO_PCI_FLAG_USE_NOTIFIERMASK_BIT)
+
  typedef struct {
      MSIMessage msg;
      int virq;
--
2.1.4




--
Marc-André Lureau

Hi marc-André,

thanks for reviewing.

I am not sure it's necessary to have a user-visible property,

I make this a user visible property, because I thought it should perhaps be
  useful to have the ability to force this behaviour on some non-pci 
bus as well,
  (since the patch that forces the option only applies to PCI buses) 
and I have
  no knowledge of non PCI buses in qemu or if vhost-user can be used on 
such
  buses.

Didier