Re: [Xen-devel] [PATCH 1/3] libxl: attach xen-pciback only to PV domains

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Oct 18, 2016 at 03:53:31AM +0200, Marek Marczykowski-Górecki wrote:
> HVM domains use IOMMU and device model assistance for communicating with
> PCI devices, xen-pcifront/pciback is used only in PV domains.

This bit of description is in line with my understanding of how PCI
passthrough works.

> When HVM domain has device model in stubdomain, attaching xen-pciback to
> the target domain itself is not only useless, but also may prevent
> attaching xen-pciback to the stubdomain, effectively breaking PCI
> passthrough.
> 
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> ---
>  tools/libxl/libxl_pci.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
> index 6f8f49c..2ae1bc4 100644
> --- a/tools/libxl/libxl_pci.c
> +++ b/tools/libxl/libxl_pci.c
> @@ -1111,7 +1111,7 @@ out:
>          }
>      }
>  
> -    if (!starting)
> +    if (!starting && !hvm)
>          rc = libxl__device_pci_add_xenstore(gc, domid, pcidev, starting);
>      else
>          rc = 0;
> @@ -1306,7 +1306,8 @@ static void libxl__add_pcidevs(libxl__egc *egc, 
> libxl__ao *ao, uint32_t domid,
>          }
>      }
>  
> -    if (d_config->num_pcidevs > 0) {
> +    if (d_config->num_pcidevs > 0
> +            && d_config->c_info.type == LIBXL_DOMAIN_TYPE_PV) {

Please move the indentation forward.

>          rc = libxl__create_pci_backend(gc, domid, d_config->pcidevs,
>              d_config->num_pcidevs);
>          if (rc < 0) {
> -- 
> 2.5.5
> 

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