Re: [RFC PATCH] libxl/arm: Insert "xen,dev-domid" property to virtio-mmio device node

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 14 Apr 2022, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 
> This is needed for grant table based DMA ops layer (CONFIG_XEN_VIRTIO)
> at the guest side to retrieve the ID of Xen domain where the corresponding
> backend resides (it is used as an argument to the grant table APIs).
> 
> This is a part of restricted memory access under Xen feature.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

I think this looks good overall. Instead of mentioning details of the
Linux implementation, we should mention the device tree binding instead,
including a link to it. The device tree binding is the relevant spec in
this case.


> ---
> !!! This patch is based on non upstreamed yet “Virtio support for toolstack
> on Arm” series which is on review now:
> https://lore.kernel.org/xen-devel/1649442065-8332-1-git-send-email-olekstysh@xxxxxxxxx/
> 
> All details are at:
> https://lore.kernel.org/xen-devel/1649963973-22879-1-git-send-email-olekstysh@xxxxxxxxx/
> ---
>  tools/libs/light/libxl_arm.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libs/light/libxl_arm.c b/tools/libs/light/libxl_arm.c
> index 8132a47..d9b26fc 100644
> --- a/tools/libs/light/libxl_arm.c
> +++ b/tools/libs/light/libxl_arm.c
> @@ -875,7 +875,8 @@ static int make_vpci_node(libxl__gc *gc, void *fdt,
>  
>  
>  static int make_virtio_mmio_node(libxl__gc *gc, void *fdt,
> -                                 uint64_t base, uint32_t irq)
> +                                 uint64_t base, uint32_t irq,
> +                                 uint32_t backend_domid)
>  {
>      int res;
>      gic_interrupt intr;
> @@ -900,6 +901,14 @@ static int make_virtio_mmio_node(libxl__gc *gc, void 
> *fdt,
>      res = fdt_property(fdt, "dma-coherent", NULL, 0);
>      if (res) return res;
>  
> +    if (backend_domid != LIBXL_TOOLSTACK_DOMID) {
> +        uint32_t domid[1];
> +
> +        domid[0] = cpu_to_fdt32(backend_domid);
> +        res = fdt_property(fdt, "xen,dev-domid", domid, sizeof(domid));
> +        if (res) return res;
> +    }
> +
>      res = fdt_end_node(fdt);
>      if (res) return res;
>  
> @@ -1218,7 +1227,8 @@ next_resize:
>              libxl_device_disk *disk = &d_config->disks[i];
>  
>              if (disk->protocol == LIBXL_DISK_PROTOCOL_VIRTIO_MMIO)
> -                FDT( make_virtio_mmio_node(gc, fdt, disk->base, disk->irq) );
> +                FDT( make_virtio_mmio_node(gc, fdt, disk->base, disk->irq,
> +                                           disk->backend_domid) );
>          }
>  
>          if (pfdt)
> -- 
> 2.7.4
>