Subject: Re: [PATCH V9 1/9] vhost: refine vhost and vringh kconfig

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 1 Apr 2020 09:22:52 -0400

On Thu, Mar 26, 2020 at 10:01:17PM +0800, Jason Wang wrote:
> Currently, CONFIG_VHOST depends on CONFIG_VIRTUALIZATION. But vhost is
> not necessarily for VM since it's a generic userspace and kernel
> communication protocol. Such dependency may prevent archs without
> virtualization support from using vhost.
> 
> To solve this, a dedicated vhost menu is created under drivers so
> CONIFG_VHOST can be decoupled out of CONFIG_VIRTUALIZATION.
> 
> While at it, also squash Kconfig.vringh into vhost Kconfig file. This
> avoids the trick of conditional inclusion from VOP or CAIF. Then it
> will be easier to introduce new vringh users and common dependency for
> both vringh and vhost.
> 
> Signed-off-by: Jason Wang <[email-masked]>

Is this just so we can drop the dependency on CONFIG_VIRTUALIZATION?
If yes what happens if we drop this patch?
Given the impact it had I'd like to defer it till next release if
possible.

> ---
>  arch/arm/kvm/Kconfig         |  2 --
>  arch/arm64/kvm/Kconfig       |  2 --
>  arch/mips/kvm/Kconfig        |  2 --
>  arch/powerpc/kvm/Kconfig     |  2 --
>  arch/s390/kvm/Kconfig        |  4 ----
>  arch/x86/kvm/Kconfig         |  4 ----
>  drivers/Kconfig              |  2 ++
>  drivers/misc/mic/Kconfig     |  4 ----
>  drivers/net/caif/Kconfig     |  4 ----
>  drivers/vhost/Kconfig        | 23 ++++++++++++++---------
>  drivers/vhost/Kconfig.vringh |  6 ------
>  11 files changed, 16 insertions(+), 39 deletions(-)
>  delete mode 100644 drivers/vhost/Kconfig.vringh
> 
> diff --git a/arch/arm/kvm/Kconfig b/arch/arm/kvm/Kconfig
> index f591026347a5..be97393761bf 100644
> --- a/arch/arm/kvm/Kconfig
> +++ b/arch/arm/kvm/Kconfig
> @@ -54,6 +54,4 @@ config KVM_ARM_HOST
>  	---help---
>  	  Provides host support for ARM processors.
>  
> -source "drivers/vhost/Kconfig"
> -
>  endif # VIRTUALIZATION
> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
> index a475c68cbfec..449386d76441 100644
> --- a/arch/arm64/kvm/Kconfig
> +++ b/arch/arm64/kvm/Kconfig
> @@ -64,6 +64,4 @@ config KVM_ARM_PMU
>  config KVM_INDIRECT_VECTORS
>         def_bool KVM && (HARDEN_BRANCH_PREDICTOR || HARDEN_EL2_VECTORS)
>  
> -source "drivers/vhost/Kconfig"
> -
>  endif # VIRTUALIZATION
> diff --git a/arch/mips/kvm/Kconfig b/arch/mips/kvm/Kconfig
> index eac25aef21e0..b91d145aa2d5 100644
> --- a/arch/mips/kvm/Kconfig
> +++ b/arch/mips/kvm/Kconfig
> @@ -72,6 +72,4 @@ config KVM_MIPS_DEBUG_COP0_COUNTERS
>  
>  	  If unsure, say N.
>  
> -source "drivers/vhost/Kconfig"
> -
>  endif # VIRTUALIZATION
> diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
> index 711fca9bc6f0..12885eda324e 100644
> --- a/arch/powerpc/kvm/Kconfig
> +++ b/arch/powerpc/kvm/Kconfig
> @@ -204,6 +204,4 @@ config KVM_XIVE
>  	default y
>  	depends on KVM_XICS && PPC_XIVE_NATIVE && KVM_BOOK3S_HV_POSSIBLE
>  
> -source "drivers/vhost/Kconfig"
> -
>  endif # VIRTUALIZATION
> diff --git a/arch/s390/kvm/Kconfig b/arch/s390/kvm/Kconfig
> index d3db3d7ed077..def3b60f1fe8 100644
> --- a/arch/s390/kvm/Kconfig
> +++ b/arch/s390/kvm/Kconfig
> @@ -55,8 +55,4 @@ config KVM_S390_UCONTROL
>  
>  	  If unsure, say N.
>  
> -# OK, it's a little counter-intuitive to do this, but it puts it neatly under
> -# the virtualization menu.
> -source "drivers/vhost/Kconfig"
> -
>  endif # VIRTUALIZATION
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 991019d5eee1..0dfe70e17af9 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -94,8 +94,4 @@ config KVM_MMU_AUDIT
>  	 This option adds a R/W kVM module parameter 'mmu_audit', which allows
>  	 auditing of KVM MMU events at runtime.
>  
> -# OK, it's a little counter-intuitive to do this, but it puts it neatly under
> -# the virtualization menu.
> -source "drivers/vhost/Kconfig"
> -
>  endif # VIRTUALIZATION
> diff --git a/drivers/Kconfig b/drivers/Kconfig
> index 8befa53f43be..7a6d8b2b68b4 100644
> --- a/drivers/Kconfig
> +++ b/drivers/Kconfig
> @@ -138,6 +138,8 @@ source "drivers/virt/Kconfig"
>  
>  source "drivers/virtio/Kconfig"
>  
> +source "drivers/vhost/Kconfig"
> +
>  source "drivers/hv/Kconfig"
>  
>  source "drivers/xen/Kconfig"
> diff --git a/drivers/misc/mic/Kconfig b/drivers/misc/mic/Kconfig
> index b6841ba6d922..8f201d019f5a 100644
> --- a/drivers/misc/mic/Kconfig
> +++ b/drivers/misc/mic/Kconfig
> @@ -133,8 +133,4 @@ config VOP
>  	  OS and tools for MIC to use with this driver are available from
>  	  <http://software.intel.com/en-us/mic-developer>.
>  
> -if VOP
> -source "drivers/vhost/Kconfig.vringh"
> -endif
> -
>  endmenu
> diff --git a/drivers/net/caif/Kconfig b/drivers/net/caif/Kconfig
> index e74e2bb61236..9db0570c5beb 100644
> --- a/drivers/net/caif/Kconfig
> +++ b/drivers/net/caif/Kconfig
> @@ -58,8 +58,4 @@ config CAIF_VIRTIO
>  	---help---
>  	  The CAIF driver for CAIF over Virtio.
>  
> -if CAIF_VIRTIO
> -source "drivers/vhost/Kconfig.vringh"
> -endif
> -
>  endif # CAIF_DRIVERS
> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
> index 3d03ccbd1adc..4aef10a54cd1 100644
> --- a/drivers/vhost/Kconfig
> +++ b/drivers/vhost/Kconfig
> @@ -1,8 +1,20 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> +config VHOST_RING
> +	tristate
> +	help
> +	  This option is selected by any driver which needs to access
> +	  the host side of a virtio ring.
> +
> +menuconfig VHOST
> +	tristate "Host kernel accelerator for virtio (VHOST)"
> +	help
> +	  This option is selected by any driver which needs to access
> +	  the core of vhost.
> +if VHOST
> +

The description here is wrong, isn't it?
VHOST and VHOST_RING are no longer selected, right?

>  config VHOST_NET
>  	tristate "Host kernel accelerator for virtio net"
>  	depends on NET && EVENTFD && (TUN || !TUN) && (TAP || !TAP)
> -	select VHOST
>  	---help---
>  	  This kernel module can be loaded in host kernel to accelerate
>  	  guest networking with virtio_net. Not to be confused with virtio_net
> @@ -14,7 +26,6 @@ config VHOST_NET
>  config VHOST_SCSI
>  	tristate "VHOST_SCSI TCM fabric driver"
>  	depends on TARGET_CORE && EVENTFD
> -	select VHOST
>  	default n
>  	---help---
>  	Say M here to enable the vhost_scsi TCM fabric module
> @@ -24,7 +35,6 @@ config VHOST_VSOCK
>  	tristate "vhost virtio-vsock driver"
>  	depends on VSOCKETS && EVENTFD
>  	select VIRTIO_VSOCKETS_COMMON
> -	select VHOST
>  	default n
>  	---help---
>  	This kernel module can be loaded in the host kernel to provide AF_VSOCK
> @@ -34,12 +44,6 @@ config VHOST_VSOCK
>  	To compile this driver as a module, choose M here: the module will be called
>  	vhost_vsock.
>  
> -config VHOST
> -	tristate
> -	---help---
> -	  This option is selected by any driver which needs to access
> -	  the core of vhost.
> -
>  config VHOST_CROSS_ENDIAN_LEGACY
>  	bool "Cross-endian support for vhost"
>  	default n
> @@ -54,3 +58,4 @@ config VHOST_CROSS_ENDIAN_LEGACY
>  	  adds some overhead, it is disabled by default.
>  
>  	  If unsure, say "N".
> +endif
> diff --git a/drivers/vhost/Kconfig.vringh b/drivers/vhost/Kconfig.vringh
> deleted file mode 100644
> index c1fe36a9b8d4..000000000000
> --- a/drivers/vhost/Kconfig.vringh
> +++ /dev/null
> @@ -1,6 +0,0 @@
> -# SPDX-License-Identifier: GPL-2.0-only
> -config VHOST_RING
> -	tristate
> -	---help---
> -	  This option is selected by any driver which needs to access
> -	  the host side of a virtio ring.
> -- 
> 2.20.1