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

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 01.04.20 17:57, Michael S. Tsirkin wrote:
> On Wed, Apr 01, 2020 at 10:50:50PM +0800, Jason Wang wrote:
>>
>> On 2020/4/1 下午10:27, Michael S. Tsirkin wrote:
>>> On Wed, Apr 01, 2020 at 10:13:29PM +0800, Jason Wang wrote:
>>>> On 2020/4/1 下午9:02, Christian Borntraeger wrote:
>>>>> On 01.04.20 14:56, Christian Borntraeger wrote:
>>>>>> On 01.04.20 14:50, Jason Wang wrote:
>>>>>>> On 2020/4/1 下午7:21, Christian Borntraeger wrote:
>>>>>>>> On 26.03.20 15:01, 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.
>>>>>>>> FWIW, this now results in vhost not being build with defconfig kernels (in todays
>>>>>>>> linux-next).
>>>>>>>>
>>>>>>> Hi Christian:
>>>>>>>
>>>>>>> Did you meet it even with this commit https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=a4be40cbcedba9b5b714f3c95182e8a45176e42d?
>>>>>> I simply used linux-next. The defconfig does NOT contain CONFIG_VHOST and therefore CONFIG_VHOST_NET and friends
>>>>>> can not be selected.
>>>>>>
>>>>>> $ git checkout next-20200401
>>>>>> $ make defconfig
>>>>>>     HOSTCC  scripts/basic/fixdep
>>>>>>     HOSTCC  scripts/kconfig/conf.o
>>>>>>     HOSTCC  scripts/kconfig/confdata.o
>>>>>>     HOSTCC  scripts/kconfig/expr.o
>>>>>>     LEX     scripts/kconfig/lexer.lex.c
>>>>>>     YACC    scripts/kconfig/parser.tab.[ch]
>>>>>>     HOSTCC  scripts/kconfig/lexer.lex.o
>>>>>>     HOSTCC  scripts/kconfig/parser.tab.o
>>>>>>     HOSTCC  scripts/kconfig/preprocess.o
>>>>>>     HOSTCC  scripts/kconfig/symbol.o
>>>>>>     HOSTCC  scripts/kconfig/util.o
>>>>>>     HOSTLD  scripts/kconfig/conf
>>>>>> *** Default configuration is based on 'x86_64_defconfig'
>>>>>> #
>>>>>> # configuration written to .config
>>>>>> #
>>>>>>
>>>>>> $ grep VHOST .config
>>>>>> # CONFIG_VHOST is not set
>>>>>>
>>>>>>> If yes, what's your build config looks like?
>>>>>>>
>>>>>>> Thanks
>>>>> This was x86. Not sure if that did work before.
>>>>> On s390 this is definitely a regression as the defconfig files
>>>>> for s390 do select VHOST_NET
>>>>>
>>>>> grep VHOST arch/s390/configs/*
>>>>> arch/s390/configs/debug_defconfig:CONFIG_VHOST_NET=m
>>>>> arch/s390/configs/debug_defconfig:CONFIG_VHOST_VSOCK=m
>>>>> arch/s390/configs/defconfig:CONFIG_VHOST_NET=m
>>>>> arch/s390/configs/defconfig:CONFIG_VHOST_VSOCK=m
>>>>>
>>>>> and this worked with 5.6, but does not work with next. Just adding
>>>>> CONFIG_VHOST=m to the defconfig solves the issue, something like
>>>>
>>>> Right, I think we probably need
>>>>
>>>> 1) add CONFIG_VHOST=m to all defconfigs that enables
>>>> CONFIG_VHOST_NET/VSOCK/SCSI.
>>>>
>>>> or
>>>>
>>>> 2) don't use menuconfig for CONFIG_VHOST, let NET/SCSI/VDPA just select it.
>>>>
>>>> Thanks
>>> OK I tried this:
>>>
>>> diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
>>> index 2523a1d4290a..a314b900d479 100644
>>> --- a/drivers/vhost/Kconfig
>>> +++ b/drivers/vhost/Kconfig
>>> @@ -19,11 +19,10 @@ menuconfig VHOST
>>>   	  This option is selected by any driver which needs to access
>>>   	  the core of vhost.
>>> -if VHOST
>>> -
>>>   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
>>> @@ -35,6 +34,7 @@ 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
>>> @@ -44,6 +44,7 @@ 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
>>> @@ -57,6 +58,7 @@ config VHOST_VDPA
>>>   	tristate "Vhost driver for vDPA-based backend"
>>>   	depends on EVENTFD
>>>   	select VDPA
>>> +	select VHOST
>>>   	help
>>>   	  This kernel module can be loaded in host kernel to accelerate
>>>   	  guest virtio devices with the vDPA-based backends.
>>> @@ -78,5 +80,3 @@ config VHOST_CROSS_ENDIAN_LEGACY
>>>   	  adds some overhead, it is disabled by default.
>>>   	  If unsure, say "N".
>>> -
>>> -endif
>>>
>>>
>>> But now CONFIG_VHOST is always "y", never "m".
>>> Which I think will make it a built-in.
>>> Didn't figure out why yet.
>>
>>
>> Is it because the dependency of EVENTFD for CONFIG_VHOST?
> 
> Oh no, it's because I forgot to change menuconfig to config.
> 
> 
>> Remove that one for this patch, I can get CONFIG_VHOST=m.

FWIW, the current vhost/linux-next branch seems to work again.