virt/steal_governor: Enable the driver

Provide a config option to enable the steal_governor driver.
Since the feature targets paravirtualized environments and requires SMP,
enforce those dependencies. The driver selects CONFIG_PREFERRED_CPU
for the core scheduler mechanisms to work.

It is recommended to build the driver as a module (m) instead of
built-in (y) due to the following reasons:

- Module parameters are read-only after initialization. Building as a
  module allows updating these parameters by simply reloading the module.
  Default module parameters cannot work in all configurations.

- The driver can be completely disabled by unloading the module.

- This feature works best when all VMs operate in a cooperative manner.
  Requiring an explicit module load ensures intentional deployment
  across all VMs by the system administrator.

Suggested-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260928053728.797539-14-sshegde@linux.ibm.com

drivers/virt/Kconfig

@@ -41,6 +41,23 @@ config FSL_HV_MANAGER
           4) A kernel interface for receiving callbacks when a managed
 	     partition shuts down.
 
+config STEAL_GOVERNOR
+	tristate "Dynamic vCPU management based on steal time"
+	depends on PARAVIRT && SMP
+	select PREFERRED_CPU
+	default m
+	help
+	  This driver helps to reduce the steal time in paravirtualized
+	  environments, thereby reducing vCPU preemption costs.
+
+	  By default preferred CPUs will be same as active CPUs. Depending
+	  on the steal time when steal_governor driver is enabled,
+	  preferred CPUs could become subset of active CPUs.
+	  More details are at: Documentation/driver-api/steal-governor.rst
+
+	  It is recommended to build it as module and load the module
+	  to enable it.
+
 source "drivers/virt/vboxguest/Kconfig"
 
 source "drivers/virt/nitro_enclaves/Kconfig"

drivers/virt/Makefile

@@ -5,6 +5,7 @@
 
 obj-$(CONFIG_FSL_HV_MANAGER)	+= fsl_hypervisor.o
 obj-$(CONFIG_VMGENID)		+= vmgenid.o
+obj-$(CONFIG_STEAL_GOVERNOR)	+= steal_governor.o
 obj-y				+= vboxguest/
 
 obj-$(CONFIG_NITRO_ENCLAVES)	+= nitro_enclaves/