bhyve: Document the hw.vmm.maxcpu tunable and the current limit on vCPUs

Reviewed by:	corvink (original version)
Co-authored-by: John Baldwin <jhb@FreeBSD.org>
Differential Revision:	https://reviews.freebsd.org/D40074

share/man/man4/vmm.4

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd December 19, 2013
+.Dd October 12, 2023
 .Dt VMM 4
 .Os
 .Sh NAME
@@ -79,6 +79,16 @@ The
 and
 .Va pptdevs3
 variables can be used for additional entries.
+.Sh LOADER TUNABLES
+Tunables can be set at the
+.Xr loader 8
+prompt before booting the kernel or stored in
+.Xr loader.conf 5 .
+.Bl -tag -width indent
+.It Va hw.vmm.maxcpu
+Maximum number of virtual CPUs.
+The default is the number of physical CPUs in the system.
+.El
 .Sh EXAMPLES
 Reserve three PCI devices for use by the hypervisor: bus 10 slot 0 function 0,
 bus 6 slot 5 function 0, and bus 6 slot 5 function 1.

usr.sbin/bhyve/bhyve.8

@@ -22,7 +22,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd October 9, 2023
+.Dd October 12, 2023
 .Dt BHYVE 8
 .Os
 .Sh NAME
@@ -129,7 +129,6 @@ The default value for each of
 and
 .Ar threads
 is 1.
-The current maximum number of guest virtual CPUs is 16.
 If
 .Ar numcpus
 is not specified then it will be calculated from the other arguments.
@@ -143,6 +142,15 @@ and
 If a
 .Ar setting
 is specified more than once the last one has precedence.
+.Pp
+The maximum number of virtual CPUs defaults to the number of active
+physical CPUs in the system available via the
+.Va hw.vmm.maxcpu
+.Xr sysctl 8
+variable.
+The limit can be adjusted via the
+.Va hw.vmm.maxcpu
+loader tunable.
 .It Fl D
 Destroy the VM on guest initiated power-off.
 .It Fl e