Re: [Qemu-devel] [PATCH] vfio/pci: fix out-of-sync BAR information on reset

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 21 Oct 2016 13:00:33 -0400
Ido Yariv <ido@wizery.com> wrote:

> When a PCI device is reset, pci_do_device_reset resets all BAR addresses
> in the relevant PCIDevice's config buffer.
> 
> The VFIO configuration space stays untouched, so the guest OS may choose
> to skip restoring the BAR addresses as they would seem intact. The PCI
> device may be left non-operational.
> One example of such a scenario is when the guest exits S3.
> 
> Fix this by resetting the BAR addresses in the VFIO configuration space
> as well.
> 
> Signed-off-by: Ido Yariv <ido@wizery.com>
> ---
>  hw/vfio/pci.c | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 65d30fd..9e1dee0 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1922,11 +1922,41 @@ static void vfio_pci_pre_reset(VFIOPCIDevice *vdev)
>  static void vfio_pci_post_reset(VFIOPCIDevice *vdev)
>  {
>      Error *err = NULL;
> +    int nr;
>  
>      vfio_intx_enable(vdev, &err);
>      if (err) {
>          error_reportf_err(err, ERR_PREFIX, vdev->vbasedev.name);
>      }
> +
> +    for (nr = 0; nr < PCI_NUM_REGIONS - 1; ++nr) {
> +        VFIOBAR *bar = &vdev->bars[nr];
> +        off_t addr = vdev->config_offset + PCI_BASE_ADDRESS_0 + (4 * nr);
> +        uint32_t org = 0;
> +        uint64_t val = 0;
> +        uint32_t len;
> +
> +        if (!bar->region.size) {
> +            continue;
> +        }
> +
> +        if (pread(vdev->vbasedev.fd, &org, sizeof(org), addr) < 0) {
> +            error_report("%s(%s) read bar %d failed: %m", __func__,
> +                         vdev->vbasedev.name, nr);
> +            continue;
> +        }
> +
> +        val = le32_to_cpu(org);
> +        val &= (bar->ioport ? ~PCI_BASE_ADDRESS_IO_MASK :
> +                              ~PCI_BASE_ADDRESS_MEM_MASK);
> +        val = cpu_to_le64(val);
> +
> +        len = bar->mem64 ? sizeof(uint64_t) : sizeof(uint32_t);
> +        if (pwrite(vdev->vbasedev.fd, &val, len, addr) != len) {
> +            error_report("%s(%s) reset bar %d failed: %m", __func__,
> +                         vdev->vbasedev.name, nr);
> +        }
> +    }

Why do we care to be so precise, can't we just blindly do 4-byte writes
of zero to each of the 6 BAR registers?  The bits you're trying to
preserve should be read-only anyway.  Nothing is saved by trying to do
an 8-byte write for 64-bit BARs.  Thanks,

Alex

>  }
>  
>  static bool vfio_pci_host_match(PCIHostDeviceAddress *addr, const char *name)