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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 1 Apr 2020 10:13:14 -0400

On Wed, Apr 01, 2020 at 10:08:59PM +0800, Jason Wang wrote:
> 
> On 2020/4/1 下午9:22, Michael S. Tsirkin wrote:
> > 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?
> 
> 
> The problem is that then VHOST_RING must depend on CONFIG_VIRTUALIZATION
> (which enable VHOST_IOTLB) to work.
> 
> But it looks to me CAIF and VOP doesn't requires CONFIG_VIRTUALIZATION.

How about stubs for IOTLB so VHOST_RING does not depend on VHOST_IOTLB?
I'm pretty sure neither user of vringh can actually use IOTLB, it's a
software only thing.

> 
> > 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?
> 
> 
> For VHOST not currently.

Can we just bring it back and select it?

> For VHOST_RING, it was selected by CAIF, VOP and VDPASIM.
> 
> Thanks
> 
> 
> > 
> > 
> > >   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