During migration restoring, vfio_enable_vectors() is called to restore
enabling MSI-X interrupts for assigned devices. It sets the range from
0 to nr_vectors to kernel to enable MSI-X and the vectors unmasked in
guest. During the MSI-X enabling, all the vectors within the range are
allocated according to the VFIO_DEVICE_SET_IRQS ioctl.
When dynamic MSI-X allocation is supported, we only want the guest
unmasked vectors being allocated and enabled. Use vector 0 with an
invalid fd to get MSI-X enabled, after that, all the vectors can be
allocated in need.
Signed-off-by: Jing Liu <jing2....@intel.com>
Reviewed-by: Cédric Le Goater <c...@redhat.com>
Reviewed-by: Alex Williamson <alex.william...@redhat.com>
---
Changes since v2:
- Apply Cédric's Reviewed-by.
- Apply Alex's Reviewed-by.
Changes since v1:
- No change.
Changes since RFC v1:
- Revise the comments. (Alex)
- Call the new helper function in previous patch to enable MSI-X. (Alex)
---
hw/vfio/pci.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index bf676a49ae77..8a082af39e77 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -402,6 +402,23 @@ static int vfio_enable_vectors(VFIOPCIDevice *vdev, bool
msix)
int ret = 0, i, argsz;
int32_t *fds;
+ /*
+ * If dynamic MSI-X allocation is supported, the vectors to be allocated
+ * and enabled can be scattered. Before kernel enabling MSI-X, setting
+ * nr_vectors causes all these vectors to be allocated on host.
+ *
+ * To keep allocation as needed, use vector 0 with an invalid fd to get
+ * MSI-X enabled first, then set vectors with a potentially sparse set of
+ * eventfds to enable interrupts only when enabled in guest.
+ */
+ if (msix && !vdev->msix->noresize) {
+ ret = vfio_enable_msix_no_vec(vdev);
+
+ if (ret) {
+ return ret;
+ }
+ }
+
argsz = sizeof(*irq_set) + (vdev->nr_vectors * sizeof(*fds));
irq_set = g_malloc0(argsz);
--
2.27.0
