From e71b8aac80271011c1248a32782452c02bb23198 Mon Sep 17 00:00:00 2001

From: Alex Williamson <alex.williamson@redhat.com>

Date: Thu, 7 Aug 2014 21:03:14 +0200

Subject: [PATCH 6/7] vfio: Fix MSI-X vector expansion

Message-id: <20140807210314.11689.89693.stgit@gimli.home>

Patchwork-id: 60482

O-Subject: [RHEL7.0/z qemu-kvm PATCH v2 5/6] vfio: Fix MSI-X vector expansion

Bugzilla: 1098976

RH-Acked-by: Bandan Das <bsd@redhat.com>

RH-Acked-by: Amos Kong <akong@redhat.com>

RH-Acked-by: Laszlo Ersek <lersek@redhat.com>

When new MSI-X vectors are enabled we need to disable MSI-X and

re-enable it with the correct number of vectors.  That means we need

to reprogram the eventfd triggers for each vector.  Prior to f4d45d47

vector->use tracked whether a vector was masked or unmasked and we

could always pick the KVM path when available for unmasked vectors.

Now vfio doesn't track mask state itself and vector->use and virq

remains configured even for masked vectors.  Therefore we need to ask

the MSI-X code whether a vector is masked in order to select the

correct signaling path.  As noted in the comment, MSI relies on

hardware to handle masking.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Cc: qemu-stable@nongnu.org # QEMU 2.1

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 hw/misc/vfio.c | 38 +++++++++++++++++++++++++++++---------

 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c

index bd37924..688e2ef 100644

--- a/hw/misc/vfio.c

+++ b/hw/misc/vfio.c

@@ -119,11 +119,20 @@ typedef struct VFIOINTx {

 } VFIOINTx;

 typedef struct VFIOMSIVector {

-    EventNotifier interrupt; /* eventfd triggered on interrupt */

-    EventNotifier kvm_interrupt; /* eventfd triggered for KVM irqfd bypass */

+    /*

+     * Two interrupt paths are configured per vector.  The first, is only used

+     * for interrupts injected via QEMU.  This is typically the non-accel path,

+     * but may also be used when we want QEMU to handle masking and pending

+     * bits.  The KVM path bypasses QEMU and is therefore higher performance,

+     * but requires masking at the device.  virq is used to track the MSI route

+     * through KVM, thus kvm_interrupt is only available when virq is set to a

+     * valid (>= 0) value.

+     */

+    EventNotifier interrupt;

+    EventNotifier kvm_interrupt;

     struct VFIODevice *vdev; /* back pointer to device */

     MSIMessage msg; /* cache the MSI message so we know when it changes */

-    int virq; /* KVM irqchip route for QEMU bypass */

+    int virq;

     bool use;

 } VFIOMSIVector;

@@ -662,13 +671,24 @@ static int vfio_enable_vectors(VFIODevice *vdev, bool msix)

     fds = (int32_t *)&irq_set->data;

     for (i = 0; i < vdev->nr_vectors; i++) {

-        if (!vdev->msi_vectors[i].use) {

-            fds[i] = -1;

-        } else if (vdev->msi_vectors[i].virq >= 0) {

-            fds[i] = event_notifier_get_fd(&vdev->msi_vectors[i].kvm_interrupt);

-        } else {

-            fds[i] = event_notifier_get_fd(&vdev->msi_vectors[i].interrupt);

+        int fd = -1;

+

+        /*

+         * MSI vs MSI-X - The guest has direct access to MSI mask and pending

+         * bits, therefore we always use the KVM signaling path when setup.

+         * MSI-X mask and pending bits are emulated, so we want to use the

+         * KVM signaling path only when configured and unmasked.

+         */

+        if (vdev->msi_vectors[i].use) {

+            if (vdev->msi_vectors[i].virq < 0 ||

+                (msix && msix_is_masked(&vdev->pdev, i))) {

+                fd = event_notifier_get_fd(&vdev->msi_vectors[i].interrupt);

+            } else {

+                fd = event_notifier_get_fd(&vdev->msi_vectors[i].kvm_interrupt);

+            }

         }

+

+        fds[i] = fd;

     }

     ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, irq_set);

-- 

1.8.3.1