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

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Message-ID: <be04a26f-866d-43e6-9a0b-15b91405503e@linux.microsoft.com>
Date: Wed, 7 May 2025 16:51:50 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: 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: Roman Kisel <romank@...ux.microsoft.com>,
 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 3:49 PM, Saurabh Singh Sengar wrote:
>> Provide an interface for Virtual Machine Monitor like OpenVMM and its
>> use as OpenHCL paravisor to control VTL0 (Virtual trust Level).
>> Expose devices and support IOCTLs for features like VTL creation,
>> VTL0 memory management, context switch, making hypercalls,
>> mapping VTL0 address space to VTL2 userspace, getting new VMBus
>> messages and channel events in VTL2 etc.
>>
>> Co-developed-by: Roman Kisel <romank@...ux.microsoft.com>
>> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>
>> Co-developed-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
>> Signed-off-by: Saurabh Sengar <ssengar@...ux.microsoft.com>
>> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
>> ---
>>
>> OpenVMM :
>> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fopenv
>> mm.dev%2Fguide%2F&data=05%7C02%7Cssengar%40microsoft.com%7Ce3b
>> 0a61c2c72423aa33408dd8c7af2e9%7C72f988bf86f141af91ab2d7cd011db47%
>> 7C1%7C0%7C638821181946438191%7CUnknown%7CTWFpbGZsb3d8eyJFbXB
>> 0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFp
>> bCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=uYUgaqKTazf0BL8ukdeUEor
>> d9hN8NidMLwE19NdprlE%3D&reserved=0
>>
>> ---

<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.

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