Checking bhyve supported features (sysctls)
Rodney W. Grimes
freebsd-rwg at pdx.rh.CN85.dnsmgr.net
Thu Aug 16 16:28:09 UTC 2018
> Text manually wrapped to 80, any broken quoting is my fault - rwg
> > > Hello,
> > >
> > > I'm looking for better ways to check for bhyve support / available
> > > features without trying to scan through dmesg output.
> > >Yes, it would be very good to remove that, as it usually tries
> > >to grep a non-existent file /var/run/dmesg.boot that is not
> > >created until after vm_bhyve has been called from /usr/local/etc/rc.d
> > >when you have things set to autostartup >in /etc/rc.conf
> > >
> > > I notice that the following 2 sysctl's appear to be set to 1 as soon
> > > as the vmm module is loaded
> > >
> > > hw.vmm.vmx.initialized: 1
> > > hw.vmm.vmx.cap.unrestricted_guest: 1
> > >
> > > Will these be available on both Intel & AMD processors as a way
> > > to determine if the module has loaded successfully and can run guests?
> > >
> > > I also see the below sysctl related to iommu.
> > >
> > > hw.vmm.iommu.initialized
> > >
> > > Again, will this be set to 1 as soon as the module is loaded if
> > > iommu is supported, or only when it is used?
> > > There also seems to be a vmm.amdvi.enable sysctl.
> > > Would both these need checking or is vmm.iommu enough to
> > > determine support on any processor.
> > >Probalby the safest way for a shell script to decide if bhyve is
> > >up and running is to stat /dev/vmm, if that exists then the modules
> > >have loaded and initialized and bhyve should be ready to process guests.
> > Hmm, I don't get /dev/vmm unless I actually have running guests.
> I'll investigate that, I was pretty sure that you should get this
> as soon as the vmm.ko module is finished initialzing, but you might
> be right in that it takes a first vm to cause its creation.
> Confirmed, /dev/vmm does not exist until the first vm
> is created.
> > >sysctl's mentiond above would be a poor way to make this determination.
> > It would be nice if sysctls were better documented.
> > If vmx.initialized is set once vmm has successfully loaded, I can't see a better way of checking for bhyve support (assuming it's not Intel specific). This entry definitely exists and is set to 0 if you load the module on a non-supported system, and set to 1 as soon as vmm loads on my Intel test system.
> Given its undocumented status you would be relying on an
> undocumented feature that could change in either name or
> behavior, and that is not desirable.
> Let me see if I can come up with something else.
I looked at the code for bhyvectl, bhyveload and
byhve. They do not actually try to decide if vmm
is supported or not, they simply process the error
from a vm_create() or vm_open() call and exit
with an error code if they can not handle it
(some of the code can handle a vm_create failure
if infact we are trying to create a vm that
If you want to maintain full compatibility a similiar
stratergy may be in order.
Why is it that vm-bhyve specifically needs to know
if the kernel has vmm support or not?
Cant it just be written to handle the errors returned
if the supported functions do not exist?
Rod Grimes rgrimes at freebsd.org
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