From 840b740a35bf969734e0f2e44c21289fdd03079e Mon Sep 17 00:00:00 2001 From: Michael Kelley Date: Tue, 26 May 2026 07:13:04 -0700 Subject: mshv: Add conditional VMBus dependency When the VMBus driver is not part of the kernel (CONFIG_HYPERV_VMBUS=n), the MSHV root driver fails to link: ERROR: modpost: "hv_vmbus_exists" [drivers/hv/mshv_root.ko] undefined! Fix this while meeting these requirements: * It must be possible to include the MSHV root driver without the VMBus driver. In such case, the MSHV root driver can be built-in to the kernel image, or it can be built as a separate module. * If both the MSHV root driver and the VMBus driver are present, the MSHV root driver and VMBus driver can both be built-in, or they can both be separate modules. Or the MSHV root driver can be a module while the VMBus driver can be built-in, but the reverse is disallowed. Regardless of the build choices, the VMBus driver must be loaded before the MSHV driver in order for the SynIC to be managed properly (see comments in the MSHV SynIC code). The fix has two parts: * Add a Kconfig entry for MSHV_ROOT to depend on HYPERV_VMBUS if HYPERV_VMBUS is present. The entry disallows MSHV_ROOT being built-in when HYPERV_VMBUS is a module, but without requiring that HYPERV_VMBUS be built. * Add a stub implementation of hv_vmbus_exists() for when the VMBus driver is not present so that the MSHV root driver has no module dependency on VMBus. When the VMBus driver *is* present, the module dependency ensures that the VMBus driver loads first when both are built as modules. Existing code ensures that the VMBus driver loads first if it is built-in. The VMBus driver uses subsys_initcall(), which is initcall level 4. The MSHV root driver uses module_init(), which becomes device_init() when built-in, and device_init() is initcall level 6. Reported-by: Arnd Bergmann Closes: https://lore.kernel.org/all/20260520074044.923728-1-arnd@kernel.org/ Signed-off-by: Michael Kelley Acked-by: Arnd Bergmann Reviewed-by: Jork Loeser Reviewed-by: Hardik Garg Signed-off-by: Wei Liu --- include/linux/hyperv.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux') diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 41a3d82f0722..734b7ef98f4d 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -1304,7 +1304,11 @@ static inline void *hv_get_drvdata(struct hv_device *dev) struct device *hv_get_vmbus_root_device(void); +#if IS_ENABLED(CONFIG_HYPERV_VMBUS) bool hv_vmbus_exists(void); +#else +static inline bool hv_vmbus_exists(void) { return false; } +#endif struct hv_ring_buffer_debug_info { u32 current_interrupt_mask; -- cgit v1.2.3