Re: [PATCH v2 1/2] vfio/pci: Fix vfio-pci sub-page MMIO BAR mmaping in live migration

[Eric Auger]

Hi Kunkun,

On 9/14/21 3:53 AM, Kunkun Jiang wrote:
> We expand MemoryRegions of vfio-pci sub-page MMIO BARs to
> vfio_pci_write_config to improve IO performance.
s/to vfio_pci_write_config/ in vfio_pci_write_config()
> The MemoryRegions of destination VM will not be expanded
> successful in live migration, because their addresses have
s/will not be expanded successful in live migration/are not expanded
anymore after live migration (?) Is that the correct symptom?
> been updated in vmstate_load_state (vfio_pci_load_config).
>
> So iterate BARs in vfio_pci_write_config and try to update
> sub-page BARs.
>
> Fixes: c5e2fb3ce4d (vfio: Add save and load functions for VFIO PCI devices)
is it an actual fix or an optimization?
> Reported-by: Nianyao Tang <tangnianyao@huawei.com>
> Reported-by: Qixin Gan <ganqixin@huawei.com>
> Signed-off-by: Kunkun Jiang <jiangkunkun@huawei.com>
> ---
>  hw/vfio/pci.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index e1ea1d8a23..43c7e93153 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;
> +    }
what are those values before the vmstate_load_state ie. can't you do the
vfio_sub_page_bar_update_mapping() unconditionnaly on old_addr[bar] !=
pdev->io_regions[bar].addr
>  
>      ret = vmstate_load_state(f, &vmstate_vfio_pci_config, vdev, 1);
>      if (ret) {
> @@ -2463,6 +2468,14 @@ 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++) {
> +        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)) {
Thanks

Eric