linux-kernel - Re: [PATCH] Drivers: hv: Introduce mshv

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Message-ID: <29edc00e-9797-4f4a-83b3-0b4158c94a16@linux.microsoft.com>
Date: Wed, 7 May 2025 13:31:36 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: Naman Jain <namjain@...ux.microsoft.com>,
 Saurabh Singh Sengar <ssengar@...rosoft.com>,
 KY Srinivasan <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>,
 Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>
Cc: Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
 Saurabh Sengar <ssengar@...ux.microsoft.com>,
 Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
 Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: Re: [PATCH] Drivers: hv: Introduce mshv_vtl driver



On 5/7/2025 4:21 AM, Naman Jain wrote:
> 
> 

[...]

> <snip>
> 
>>> +        return -EINVAL;
>>> +    if (copy_from_user(payload, (void __user *)message.payload_ptr,
>>> +               message.payload_size))
>>> +        return -EFAULT;
>>> +
>>> +    return hv_post_message((union
>>
>> This function definition is in separate file which can be build as 
>> independent module, this will cause
>> problem while linking . Try building with CONFIG_HYPERV=m and check.
>>
>> - Saurabh
> 
> Thanks for reviewing Saurabh. As CONFIG_HYPERV can be set to 'm'
> and CONFIG_MSHV_VTL depends on it, changing CONFIG_MSHV_VTL to tristate
> and a few tweaks in Makefile will fix this issue. This will ensure that
> mshv_vtl is also built as a module when hyperv is built as a module.
> 
> I'll take care of this in next version.

Let me ask for a clarification. How would the system boot if
CONFIG_HYPERV is set to m? The arch parts are going to be still
compiled-in, correct? Otherwise I don't see how that would
initialize.

I am thinking who would load Hyper-V modules on the system
that requires Hyper-V here. It is understandable that
distro's build Hyper-V as a module. That way, they don't have to load
anything when there is no Hyper-V. Here, it is Hyper-V in and out, what
do we need to fix?

> 
> here is the diff for reference:
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 57dcfcb69b88..c7f21b483377 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -73,7 +73,7 @@ config MSHV_ROOT
>            If unsure, say N.
> 
>   config MSHV_VTL
> -       bool "Microsoft Hyper-V VTL driver"
> +       tristate "Microsoft Hyper-V VTL driver"
>          depends on HYPERV && X86_64
>          depends on TRANSPARENT_HUGEPAGE
>          depends on OF
> diff --git a/drivers/hv/Makefile b/drivers/hv/Makefile
> index 5e785dae08cc..c53a0df746b7 100644
> --- a/drivers/hv/Makefile
> +++ b/drivers/hv/Makefile
> @@ -15,9 +15,11 @@ hv_vmbus-$(CONFIG_HYPERV_TESTING)    += hv_debugfs.o
>   hv_utils-y := hv_util.o hv_kvp.o hv_snapshot.o hv_utils_transport.o
>   mshv_root-y := mshv_root_main.o mshv_synic.o mshv_eventfd.o mshv_irq.o \
>                 mshv_root_hv_call.o mshv_portid_table.o
> +mshv_vtl-y := mshv_vtl_main.o
> 
>   # Code that must be built-in
>   obj-$(subst m,y,$(CONFIG_HYPERV)) += hv_common.o
> -obj-$(subst m,y,$(CONFIG_MSHV_ROOT)) += hv_proc.o mshv_common.o
> -
> -mshv_vtl-y := mshv_vtl_main.o mshv_common.o
> +obj-$(subst m,y,$(CONFIG_MSHV_ROOT)) += hv_proc.o
> +ifneq ($(CONFIG_MSHV_ROOT) $(CONFIG_MSHV_VTL),)
> +    obj-y += mshv_common.o
> +endif
> 
> Regards,
> Naman

-- 
Thank you,
Roman