Blame SOURCES/kvm-vfio-pci-Fix-MSI-X-masking-performance.patch

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From a48a4761390e9aa917ebef7628dfc72f905910ee Mon Sep 17 00:00:00 2001
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From: Alex Williamson <alex.williamson@redhat.com>
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Date: Thu, 7 Aug 2014 21:03:08 +0200
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Subject: [PATCH 05/10] vfio-pci: Fix MSI-X masking performance
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Message-id: <20140807210308.11689.93757.stgit@gimli.home>
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Patchwork-id: 60481
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O-Subject: [RHEL7.0/z qemu-kvm PATCH v2 4/6] vfio-pci: Fix MSI-X masking performance
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Bugzilla: 1110693 1110695
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RH-Acked-by: Bandan Das <bsd@redhat.com>
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RH-Acked-by: Amos Kong <akong@redhat.com>
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RH-Acked-by: Laszlo Ersek <lersek@redhat.com>
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Upstream: f4d45d47826377722700894dbf7f47444527a9d2
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There are still old guests out there that over-exercise MSI-X masking.
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The current code completely sets-up and tears-down an MSI-X vector on
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the "use" and "release" callbacks.  While this is functional, it can
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slow an old guest to a crawl.  We can easily skip the KVM parts of
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this so that we keep the MSI route and irqfd setup.  We do however
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need to switch VFIO to trigger a different eventfd while masked.
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Actually, we have the option of continuing to use -1 to disable the
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trigger, but by using another EventNotifier we can allow the MSI-X
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core to emulate pending bits and re-fire the vector once unmasked.
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MSI code gets updated as well to use the same setup and teardown
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structures and functions.
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Prior to this change, an igbvf assigned to a RHEL5 guest gets about
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20Mbps and 50 transactions/s with netperf (remote or VF->PF).  With
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this change, we get line rate and 3k transactions/s remote or 2Gbps
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and 6k+ transactions/s to the PF.  No significant change is expected
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for newer guests with more well behaved MSI-X support.
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Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 hw/misc/vfio.c |  233 +++++++++++++++++++++++++++++++------------------------
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 1 files changed, 131 insertions(+), 102 deletions(-)
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diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
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index 5f0460a..bd37924 100644
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--- a/hw/misc/vfio.c
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+++ b/hw/misc/vfio.c
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@@ -120,6 +120,7 @@ typedef struct VFIOINTx {
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 typedef struct VFIOMSIVector {
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     EventNotifier interrupt; /* eventfd triggered on interrupt */
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+    EventNotifier kvm_interrupt; /* eventfd triggered for KVM irqfd bypass */
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     struct VFIODevice *vdev; /* back pointer to device */
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     MSIMessage msg; /* cache the MSI message so we know when it changes */
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     int virq; /* KVM irqchip route for QEMU bypass */
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@@ -663,10 +664,11 @@ static int vfio_enable_vectors(VFIODevice *vdev, bool msix)
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     for (i = 0; i < vdev->nr_vectors; i++) {
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         if (!vdev->msi_vectors[i].use) {
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             fds[i] = -1;
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-            continue;
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+        } else if (vdev->msi_vectors[i].virq >= 0) {
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+            fds[i] = event_notifier_get_fd(&vdev->msi_vectors[i].kvm_interrupt);
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+        } else {
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+            fds[i] = event_notifier_get_fd(&vdev->msi_vectors[i].interrupt);
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         }
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-
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-        fds[i] = event_notifier_get_fd(&vdev->msi_vectors[i].interrupt);
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     }
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     ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
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@@ -676,6 +678,52 @@ static int vfio_enable_vectors(VFIODevice *vdev, bool msix)
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     return ret;
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 }
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+static void vfio_add_kvm_msi_virq(VFIOMSIVector *vector, MSIMessage *msg,
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+                                  bool msix)
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+{
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+    int virq;
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+
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+    if ((msix && !VFIO_ALLOW_KVM_MSIX) ||
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+        (!msix && !VFIO_ALLOW_KVM_MSI) || !msg) {
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+        return;
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+    }
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+
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+    if (event_notifier_init(&vector->kvm_interrupt, 0)) {
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+        return;
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+    }
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+
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+    virq = kvm_irqchip_add_msi_route(kvm_state, *msg);
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+    if (virq < 0) {
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+        event_notifier_cleanup(&vector->kvm_interrupt);
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+        return;
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+    }
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+
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+    if (kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->kvm_interrupt,
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+                                       virq) < 0) {
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+        kvm_irqchip_release_virq(kvm_state, virq);
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+        event_notifier_cleanup(&vector->kvm_interrupt);
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+        return;
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+    }
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+
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+    vector->msg = *msg;
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+    vector->virq = virq;
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+}
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+
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+static void vfio_remove_kvm_msi_virq(VFIOMSIVector *vector)
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+{
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+    kvm_irqchip_remove_irqfd_notifier(kvm_state, &vector->kvm_interrupt,
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+                                      vector->virq);
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+    kvm_irqchip_release_virq(kvm_state, vector->virq);
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+    vector->virq = -1;
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+    event_notifier_cleanup(&vector->kvm_interrupt);
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+}
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+
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+static void vfio_update_kvm_msi_virq(VFIOMSIVector *vector, MSIMessage msg)
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+{
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+    kvm_irqchip_update_msi_route(kvm_state, vector->virq, msg);
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+    vector->msg = msg;
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+}
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+
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 static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
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                                    MSIMessage *msg, IOHandler *handler)
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 {
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@@ -688,30 +736,32 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
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             vdev->host.function, nr);
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     vector = &vdev->msi_vectors[nr];
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-    vector->vdev = vdev;
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-    vector->use = true;
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-
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-    msix_vector_use(pdev, nr);
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-    if (event_notifier_init(&vector->interrupt, 0)) {
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-        error_report("vfio: Error: event_notifier_init failed");
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+    if (!vector->use) {
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+        vector->vdev = vdev;
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+        vector->virq = -1;
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+        if (event_notifier_init(&vector->interrupt, 0)) {
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+            error_report("vfio: Error: event_notifier_init failed");
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+        }
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+        vector->use = true;
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+        msix_vector_use(pdev, nr);
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     }
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+    qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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+                        handler, NULL, vector);
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+
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     /*
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      * Attempt to enable route through KVM irqchip,
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      * default to userspace handling if unavailable.
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      */
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-    vector->virq = msg && VFIO_ALLOW_KVM_MSIX ?
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-                   kvm_irqchip_add_msi_route(kvm_state, *msg) : -1;
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-    if (vector->virq < 0 ||
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-        kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
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-                                       vector->virq) < 0) {
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-        if (vector->virq >= 0) {
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-            kvm_irqchip_release_virq(kvm_state, vector->virq);
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-            vector->virq = -1;
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+    if (vector->virq >= 0) {
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+        if (!msg) {
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+            vfio_remove_kvm_msi_virq(vector);
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+        } else {
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+            vfio_update_kvm_msi_virq(vector, *msg);
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         }
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-        qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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-                            handler, NULL, vector);
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+    } else {
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+        vfio_add_kvm_msi_virq(vector, msg, true);
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     }
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     /*
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@@ -742,7 +792,11 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr,
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         irq_set->count = 1;
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         pfd = (int32_t *)&irq_set->data;
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-        *pfd = event_notifier_get_fd(&vector->interrupt);
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+        if (vector->virq >= 0) {
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+            *pfd = event_notifier_get_fd(&vector->kvm_interrupt);
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+        } else {
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+            *pfd = event_notifier_get_fd(&vector->interrupt);
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+        }
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         ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
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         g_free(irq_set);
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@@ -764,50 +818,41 @@ static void vfio_msix_vector_release(PCIDevice *pdev, unsigned int nr)
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 {
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     VFIODevice *vdev = DO_UPCAST(VFIODevice, pdev, pdev);
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     VFIOMSIVector *vector = &vdev->msi_vectors[nr];
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-    int argsz;
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-    struct vfio_irq_set *irq_set;
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-    int32_t *pfd;
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     DPRINTF("%s(%04x:%02x:%02x.%x) vector %d released\n", __func__,
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             vdev->host.domain, vdev->host.bus, vdev->host.slot,
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             vdev->host.function, nr);
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     /*
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-     * XXX What's the right thing to do here?  This turns off the interrupt
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-     * completely, but do we really just want to switch the interrupt to
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-     * bouncing through userspace and let msix.c drop it?  Not sure.
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+     * There are still old guests that mask and unmask vectors on every
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+     * interrupt.  If we're using QEMU bypass with a KVM irqfd, leave all of
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+     * the KVM setup in place, simply switch VFIO to use the non-bypass
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+     * eventfd.  We'll then fire the interrupt through QEMU and the MSI-X
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+     * core will mask the interrupt and set pending bits, allowing it to
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+     * be re-asserted on unmask.  Nothing to do if already using QEMU mode.
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      */
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-    msix_vector_unuse(pdev, nr);
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-
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-    argsz = sizeof(*irq_set) + sizeof(*pfd);
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+    if (vector->virq >= 0) {
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+        int argsz;
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+        struct vfio_irq_set *irq_set;
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+        int32_t *pfd;
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-    irq_set = g_malloc0(argsz);
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-    irq_set->argsz = argsz;
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-    irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD |
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-                     VFIO_IRQ_SET_ACTION_TRIGGER;
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-    irq_set->index = VFIO_PCI_MSIX_IRQ_INDEX;
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-    irq_set->start = nr;
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-    irq_set->count = 1;
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-    pfd = (int32_t *)&irq_set->data;
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+        argsz = sizeof(*irq_set) + sizeof(*pfd);
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-    *pfd = -1;
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+        irq_set = g_malloc0(argsz);
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+        irq_set->argsz = argsz;
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+        irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD |
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+                         VFIO_IRQ_SET_ACTION_TRIGGER;
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+        irq_set->index = VFIO_PCI_MSIX_IRQ_INDEX;
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+        irq_set->start = nr;
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+        irq_set->count = 1;
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+        pfd = (int32_t *)&irq_set->data;
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-    ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
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+        *pfd = event_notifier_get_fd(&vector->interrupt);
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-    g_free(irq_set);
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+        ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
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-    if (vector->virq < 0) {
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-        qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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-                            NULL, NULL, NULL);
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-    } else {
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-        kvm_irqchip_remove_irqfd_notifier(kvm_state, &vector->interrupt,
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-                                          vector->virq);
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-        kvm_irqchip_release_virq(kvm_state, vector->virq);
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-        vector->virq = -1;
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+        g_free(irq_set);
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     }
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-
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-    event_notifier_cleanup(&vector->interrupt);
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-    vector->use = false;
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 }
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 static void vfio_enable_msix(VFIODevice *vdev)
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@@ -857,28 +902,28 @@ retry:
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         VFIOMSIVector *vector = &vdev->msi_vectors[i];
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         vector->vdev = vdev;
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+        vector->virq = -1;
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         vector->use = true;
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         if (event_notifier_init(&vector->interrupt, 0)) {
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             error_report("vfio: Error: event_notifier_init failed");
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         }
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+        qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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+                            vfio_msi_interrupt, NULL, vector);
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+
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         vector->msg = msi_get_message(&vdev->pdev, i);
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         /*
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          * Attempt to enable route through KVM irqchip,
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          * default to userspace handling if unavailable.
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          */
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-        vector->virq = VFIO_ALLOW_KVM_MSI ?
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-                       kvm_irqchip_add_msi_route(kvm_state, vector->msg) : -1;
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-        if (vector->virq < 0 ||
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-            kvm_irqchip_add_irqfd_notifier(kvm_state, &vector->interrupt,
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-                                           vector->virq) < 0) {
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-            qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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-                                vfio_msi_interrupt, NULL, vector);
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-        }
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+        vfio_add_kvm_msi_virq(vector, &vector->msg, false);
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     }
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+    /* Set interrupt type prior to possible interrupts */
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+    vdev->interrupt = VFIO_INT_MSI;
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+
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     ret = vfio_enable_vectors(vdev, false);
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     if (ret) {
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         if (ret < 0) {
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@@ -891,14 +936,10 @@ retry:
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         for (i = 0; i < vdev->nr_vectors; i++) {
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             VFIOMSIVector *vector = &vdev->msi_vectors[i];
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             if (vector->virq >= 0) {
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-                kvm_irqchip_remove_irqfd_notifier(kvm_state, &vector->interrupt,
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-                                                  vector->virq);
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-                kvm_irqchip_release_virq(kvm_state, vector->virq);
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-                vector->virq = -1;
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-            } else {
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-                qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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-                                    NULL, NULL, NULL);
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+                vfio_remove_kvm_msi_virq(vector);
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             }
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+            qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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+                                NULL, NULL, NULL);
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             event_notifier_cleanup(&vector->interrupt);
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         }
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@@ -910,11 +951,17 @@ retry:
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         }
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         vdev->nr_vectors = 0;
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+        /*
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+         * Failing to setup MSI doesn't really fall within any specification.
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+         * Let's try leaving interrupts disabled and hope the guest figures
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+         * out to fall back to INTx for this device.
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+         */
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+        error_report("vfio: Error: Failed to enable MSI");
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+        vdev->interrupt = VFIO_INT_NONE;
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+
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         return;
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     }
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-    vdev->interrupt = VFIO_INT_MSI;
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-
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     DPRINTF("%s(%04x:%02x:%02x.%x) Enabled %d MSI vectors\n", __func__,
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             vdev->host.domain, vdev->host.bus, vdev->host.slot,
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             vdev->host.function, vdev->nr_vectors);
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@@ -922,6 +969,20 @@ retry:
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 static void vfio_disable_msi_common(VFIODevice *vdev)
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 {
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+    int i;
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+
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+    for (i = 0; i < vdev->nr_vectors; i++) {
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+        VFIOMSIVector *vector = &vdev->msi_vectors[i];
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+        if (vdev->msi_vectors[i].use) {
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+            if (vector->virq >= 0) {
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+                vfio_remove_kvm_msi_virq(vector);
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+            }
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+            qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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+                                NULL, NULL, NULL);
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+            event_notifier_cleanup(&vector->interrupt);
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+        }
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+    }
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+
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     g_free(vdev->msi_vectors);
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     vdev->msi_vectors = NULL;
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     vdev->nr_vectors = 0;
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@@ -943,6 +1004,7 @@ static void vfio_disable_msix(VFIODevice *vdev)
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     for (i = 0; i < vdev->nr_vectors; i++) {
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         if (vdev->msi_vectors[i].use) {
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             vfio_msix_vector_release(&vdev->pdev, i);
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+            msix_vector_unuse(&vdev->pdev, i);
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         }
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     }
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@@ -958,30 +1020,7 @@ static void vfio_disable_msix(VFIODevice *vdev)
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 static void vfio_disable_msi(VFIODevice *vdev)
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 {
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-    int i;
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-
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     vfio_disable_irqindex(vdev, VFIO_PCI_MSI_IRQ_INDEX);
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-
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-    for (i = 0; i < vdev->nr_vectors; i++) {
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-        VFIOMSIVector *vector = &vdev->msi_vectors[i];
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-
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-        if (!vector->use) {
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-            continue;
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-        }
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-
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-        if (vector->virq >= 0) {
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-            kvm_irqchip_remove_irqfd_notifier(kvm_state,
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-                                              &vector->interrupt, vector->virq);
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-            kvm_irqchip_release_virq(kvm_state, vector->virq);
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-            vector->virq = -1;
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-        } else {
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-            qemu_set_fd_handler(event_notifier_get_fd(&vector->interrupt),
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-                                NULL, NULL, NULL);
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-        }
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-
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-        event_notifier_cleanup(&vector->interrupt);
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-    }
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-
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     vfio_disable_msi_common(vdev);
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     DPRINTF("%s(%04x:%02x:%02x.%x)\n", __func__, vdev->host.domain,
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@@ -1001,17 +1040,7 @@ static void vfio_update_msi(VFIODevice *vdev)
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         }
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         msg = msi_get_message(&vdev->pdev, i);
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-
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-        if (msg.address != vector->msg.address ||
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-            msg.data != vector->msg.data) {
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-
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-            DPRINTF("%s(%04x:%02x:%02x.%x) MSI vector %d changed\n",
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-                    __func__, vdev->host.domain, vdev->host.bus,
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-                    vdev->host.slot, vdev->host.function, i);
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-
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-            kvm_irqchip_update_msi_route(kvm_state, vector->virq, msg);
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-            vector->msg = msg;
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-        }
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+        vfio_update_kvm_msi_virq(vector, msg);
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     }
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 }
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-- 
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1.7.1
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