[PATCH (repost) RFC 2/2] virtio-pci: recall and return msix notifications on ISR read

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

MSIX spec requires that device can be operated with
all vectors masked, by polling pending bits.
Add APIs to recall an msix notification, and make polling
mode possible in virtio-pci by clearing the
pending bits and setting ISR appropriately on ISR read.

Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 hw/msix.c       |   26 ++++++++++++++++++++++++++
 hw/msix.h       |    3 +++
 hw/virtio-pci.c |   11 ++++++++++-
 3 files changed, 39 insertions(+), 1 deletions(-)

diff --git a/hw/msix.c b/hw/msix.c
index 63b41b9..fe967c9 100644
--- a/hw/msix.c
+++ b/hw/msix.c
@@ -349,6 +349,32 @@ void msix_notify(PCIDevice *dev, unsigned vector)
     stl_le_phys(address, data);
 }
 
+/* Recall outstanding MSI-X notifications for a vector, if possible.
+ * Return true if any were outstanding. */
+bool msix_recall(PCIDevice *dev, unsigned vector)
+{
+    bool ret;
+    if (vector >= dev->msix_entries_nr)
+        return false;
+    ret = msix_is_pending(dev, vector);
+    msix_clr_pending(dev, vector);
+    return ret;
+}
+
+/* Recall outstanding MSI-X notifications for all vectors, if possible.
+ * Return true if any were outstanding. */
+bool msix_recall_all(PCIDevice *dev)
+{
+    uint8_t ret = 0;
+    uint8_t *b;
+    for (b = dev->msix_table_page + MSIX_PAGE_PENDING;
+	 b <= msix_pending_byte(dev, dev->msix_entries_nr - 1); ++b) {
+        ret |= *b;
+        *b = 0;
+    }
+    return ret;
+}
+
 void msix_reset(PCIDevice *dev)
 {
     if (!(dev->cap_present & QEMU_PCI_CAP_MSIX))
diff --git a/hw/msix.h b/hw/msix.h
index 7e04336..86a92b1 100644
--- a/hw/msix.h
+++ b/hw/msix.h
@@ -27,6 +27,9 @@ void msix_unuse_all_vectors(PCIDevice *dev);
 
 void msix_notify(PCIDevice *dev, unsigned vector);
 
+bool msix_recall(PCIDevice *dev, unsigned vector);
+bool msix_recall_all(PCIDevice *dev);
+
 void msix_reset(PCIDevice *dev);
 
 extern int msix_supported;
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index df27c19..cab7dde 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -393,7 +393,16 @@ static uint32_t virtio_ioport_read(VirtIOPCIProxy *proxy, uint32_t addr)
         /* reading from the ISR also clears it. */
         ret = vdev->isr;
         vdev->isr = 0;
-        qemu_set_irq(proxy->pci_dev.irq[0], 0);
+        if (msix_enabled(&proxy->pci_dev)) {
+            if (msix_recall(&proxy->pci_dev, vdev->config_vector)) {
+                ret |= VIRTIO_ISR_CONFIG;
+            }
+            if (msix_recall_all(&proxy->pci_dev)) {
+                ret |= VIRTIO_ISR_VQ;
+            }
+        } else {
+		qemu_set_irq(proxy->pci_dev.irq[0], 0);
+        }
         break;
     case VIRTIO_MSI_CONFIG_VECTOR:
         ret = vdev->config_vector;
-- 
1.7.5.53.gc233e
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