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Date:   Wed, 29 Apr 2020 11:33:51 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Jason Wang <jasowang@redhat.com>, Tiwei Bie <tiwei.bie@intel.com>,
        kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vhost: fix default for vhost_iotlb
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References: <20200429142317.1847441-1-arnd@arndb.de>
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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@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