Linux Virtualization - Apr 2020 - [PATCH] vhost: fix default for vhost_iotlb

During randconfig build testing, I ran into a configuration that has
CONFIG_VHOST=m, CONFIG_VHOST_IOTLB=m and CONFIG_VHOST_RING=y, which
makes the iotlb implementation left out from vhost_ring, and in turn
leads to a link failure of the vdpa_sim module:

ERROR: modpost: "vringh_set_iotlb" [drivers/vdpa/vdpa_sim/vdpa_sim.ko]
undefined!
ERROR: modpost: "vringh_init_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
ERROR: modpost: "vringh_iov_push_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
ERROR: modpost: "vringh_iov_pull_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
ERROR: modpost: "vringh_complete_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
ERROR: modpost: "vringh_getdesc_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!

Work around it by setting the default for VHOST_IOTLB to avoid this
configuration.

Fixes: e6faeaa12841 ("vhost: drop vring dependency on iotlb")
Signed-off-by: Arnd Bergmann <arnd at arndb.de>
---
I fixed this a while ago locally but never got around to sending the
fix. If the problem has been addressed differently in the meantime,
please ignore this one.
---
 drivers/vhost/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 2c75d164b827..ee5f85761024 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 config VHOST_IOTLB
 	tristate
+	default y if VHOST=m && VHOST_RING=y
 	help
 	  Generic IOTLB implementation for vhost and vringh.
 	  This option is selected by any driver which needs to support
-- 
2.26.0

On Wed, Apr 29, 2020 at 04:23:04PM +0200, Arnd Bergmann
wrote:
> During randconfig build testing, I ran into a configuration that has
> CONFIG_VHOST=m, CONFIG_VHOST_IOTLB=m and CONFIG_VHOST_RING=y, which
> makes the iotlb implementation left out from vhost_ring, and in turn
> leads to a link failure of the vdpa_sim module:
> 
> ERROR: modpost: "vringh_set_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
> ERROR: modpost: "vringh_init_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
> ERROR: modpost: "vringh_iov_push_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
> ERROR: modpost: "vringh_iov_pull_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
> ERROR: modpost: "vringh_complete_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
> ERROR: modpost: "vringh_getdesc_iotlb"
[drivers/vdpa/vdpa_sim/vdpa_sim.ko] undefined!
> 
> Work around it by setting the default for VHOST_IOTLB to avoid this
> configuration.
> 
> Fixes: e6faeaa12841 ("vhost: drop vring dependency on iotlb")
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> ---
> I fixed this a while ago locally but never got around to sending the
> fix. If the problem has been addressed differently in the meantime,
> please ignore this one.

So I ended up not sending e6faeaa12841 upstream because of this problem.
But hey, that's a nice idea!
I'll queue something like this for the next release.
> ---
>  drivers/vhost/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index 2c75d164b827..ee5f85761024 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -1,6 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  config VHOST_IOTLB
>  	tristate
> +	default y if VHOST=m && VHOST_RING=y
>  	help
>  	  Generic IOTLB implementation for vhost and vringh.
>  	  This option is selected by any driver which needs to support
> -- 
> 2.26.0