[PULL,1/2] vfio/pci: Add support for mmapping sub-page MMIO BARs after live migration

Commit Message

Alex Williamson Nov. 1, 2021, 8:01 p.m. UTC

From: Kunkun Jiang <[e-mail]>

We can expand MemoryRegions of sub-page MMIO BARs in
vfio_pci_write_config() to improve IO performance for some
devices. However, the MemoryRegions of destination VM are
not expanded any more after live migration. Because their
addresses have been updated in vmstate_load_state()
(vfio_pci_load_config) and vfio_sub_page_bar_update_mapping()
will not be called.

This may result in poor performance after live migration.
So iterate BARs in vfio_pci_load_config() and try to update
sub-page BARs.

Reported-by: Nianyao Tang <[e-mail]>
Reported-by: Qixin Gan <[e-mail]>
Signed-off-by: Kunkun Jiang <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alex Williamson <[e-mail]>
---
 hw/vfio/pci.c |   19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

Patch

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 5cdf1d4298a7..7b45353ce27f 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -2453,7 +2453,12 @@  static int vfio_pci_load_config(VFIODevice *vbasedev, QEMUFile *f)
 {
     VFIOPCIDevice *vdev = container_of(vbasedev, VFIOPCIDevice, vbasedev);
     PCIDevice *pdev = &vdev->pdev;
-    int ret;
+    pcibus_t old_addr[PCI_NUM_REGIONS - 1];
+    int bar, ret;
+
+    for (bar = 0; bar < PCI_ROM_SLOT; bar++) {
+        old_addr[bar] = pdev->io_regions[bar].addr;
+    }
 
     ret = vmstate_load_state(f, &vmstate_vfio_pci_config, vdev, 1);
     if (ret) {
@@ -2463,6 +2468,18 @@  static int vfio_pci_load_config(VFIODevice *vbasedev, QEMUFile *f)
     vfio_pci_write_config(pdev, PCI_COMMAND,
                           pci_get_word(pdev->config + PCI_COMMAND), 2);
 
+    for (bar = 0; bar < PCI_ROM_SLOT; bar++) {
+        /*
+         * The address may not be changed in some scenarios
+         * (e.g. the VF driver isn't loaded in VM).
+         */
+        if (old_addr[bar] != pdev->io_regions[bar].addr &&
+            vdev->bars[bar].region.size > 0 &&
+            vdev->bars[bar].region.size < qemu_real_host_page_size) {
+            vfio_sub_page_bar_update_mapping(pdev, bar);
+        }
+    }
+
     if (msi_enabled(pdev)) {
         vfio_msi_enable(vdev);
     } else if (msix_enabled(pdev)) {