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From bdd720aafc6099e126b682f70e4163e1b2097594 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 21:03:14 +0200
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Subject: [PATCH 06/10] vfio: Fix MSI-X vector expansion
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Message-id: <20140807210314.11689.89693.stgit@gimli.home>
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Patchwork-id: 60482
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O-Subject: [RHEL7.0/z qemu-kvm PATCH v2 5/6] vfio: Fix MSI-X vector expansion
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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: c048be5cc92ae201c339d46984476c4629275ed6
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When new MSI-X vectors are enabled we need to disable MSI-X and
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re-enable it with the correct number of vectors.  That means we need
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to reprogram the eventfd triggers for each vector.  Prior to f4d45d47
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vector->use tracked whether a vector was masked or unmasked and we
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could always pick the KVM path when available for unmasked vectors.
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Now vfio doesn't track mask state itself and vector->use and virq
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remains configured even for masked vectors.  Therefore we need to ask
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the MSI-X code whether a vector is masked in order to select the
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correct signaling path.  As noted in the comment, MSI relies on
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hardware to handle masking.
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Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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Cc: qemu-stable@nongnu.org # QEMU 2.1
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 hw/misc/vfio.c |   38 +++++++++++++++++++++++++++++---------
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 1 files changed, 29 insertions(+), 9 deletions(-)
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diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
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index bd37924..688e2ef 100644
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--- a/hw/misc/vfio.c
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+++ b/hw/misc/vfio.c
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@@ -119,11 +119,20 @@ typedef struct VFIOINTx {
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 } 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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+    /*
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+     * Two interrupt paths are configured per vector.  The first, is only used
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+     * for interrupts injected via QEMU.  This is typically the non-accel path,
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+     * but may also be used when we want QEMU to handle masking and pending
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+     * bits.  The KVM path bypasses QEMU and is therefore higher performance,
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+     * but requires masking at the device.  virq is used to track the MSI route
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+     * through KVM, thus kvm_interrupt is only available when virq is set to a
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+     * valid (>= 0) value.
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+     */
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+    EventNotifier interrupt;
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+    EventNotifier kvm_interrupt;
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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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+    int virq;
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     bool use;
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 } VFIOMSIVector;
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@@ -662,13 +671,24 @@ static int vfio_enable_vectors(VFIODevice *vdev, bool msix)
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     fds = (int32_t *)&irq_set->data;
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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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-        } 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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+        int fd = -1;
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+
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+        /*
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+         * MSI vs MSI-X - The guest has direct access to MSI mask and pending
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+         * bits, therefore we always use the KVM signaling path when setup.
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+         * MSI-X mask and pending bits are emulated, so we want to use the
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+         * KVM signaling path only when configured and unmasked.
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+         */
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+        if (vdev->msi_vectors[i].use) {
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+            if (vdev->msi_vectors[i].virq < 0 ||
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+                (msix && msix_is_masked(&vdev->pdev, i))) {
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+                fd = event_notifier_get_fd(&vdev->msi_vectors[i].interrupt);
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+            } else {
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+                fd = event_notifier_get_fd(&vdev->msi_vectors[i].kvm_interrupt);
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+            }
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         }
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+
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+        fds[i] = fd;
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     }
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     ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);
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-- 
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1.7.1
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