-----Original Message----- From: [email protected] <[email protected]> On Behalf Of Marcelo Araujo Sent: 17 August 2018 10:14 To: Matt Churchyard <[email protected]> Cc: [email protected] Subject: Re: Checking bhyve supported features (sysctls)
2018-08-17 16:54 GMT+08:00 Matt Churchyard <[email protected]>: > > > > > 2018-08-17 16:25 GMT+08:00 Matt Churchyard <[email protected]>: > > -----Original Message----- > From: [email protected] < > [email protected]> On Behalf Of Rodney W. > Grimes > Sent: 16 August 2018 18:31 > To: Allan Jude <[email protected]> > Cc: Matt Churchyard <[email protected]>; > freebsd-virtualization@ freebsd.org > Subject: Re: Checking bhyve supported features (sysctls) > > > On August 16, 2018 5:28:05 PM GMT+01:00, "Rodney W. Grimes" < > [email protected]> wrote: > > >> > > >> 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. > > >> > > >> Agreed. > > >> > > >> > 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 already exists). > > > > > >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? > > > > I think the question vm-bhyve wants to answer is: does the CPU have > > the required features to run a multicore VM. > > >Why does it need to know that? If it tries to start a > >multicore/thread > VM and the system can not support it an error is returned and the > bhyve command fails. > > >Actually determining that specific issue is non-trivial iirc as some > >vmm > supported CPU's can only run a single VM with a single thread in that > VM (early core cpu's). > > > > > These or similar sysctls do seem to be the correct way to > > communicate that support. > > >I do not believe any of those sysctl's communicate that your on a > >broken > cpu or to what extent you can run vm's with multiple threads. > > So cap.unrestricted_guest from the vmm "capabilities" set of sysctls > is not a valid way to determine if the host has unrestricted guest > support (required for non-freebsd or multicore freebsd guests, and as > you say missing from some early VT-x capable processors)? > > >I went and looked at why vm-bhyve is groveling around in > /var/run/dmesg.boot and found that it is simply trying to determine if > the host CPU is vmm capable, > >specifically: > >util::check_bhyve_support(){ > >... > > >These checks are already built into the kernel. > >This can all go in the bit bucket, if you try to start a VM on an > unsupported system an error is returned, recoding this in shell is > just setting yourself up for "future" bugs. > > The kernel knows what features are supported but does not expose > these, so all I can do is similar to libvirt and run bhyve with > different options to see what errors pop up. > I think I'll just remove all checking for now and let users discover > the issue for themselves if bhyve won't run. Hopefully the > vmx.initialized / > cap.* sysctls will at some point become a defined way of seeing if vmm > is ready / testing for vmm features, as apparently these serve no > purpose at the moment. > > Matt > > _______________________________________________ > [email protected] mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-virtualization > To unsubscribe, send any mail to "freebsd-virtualization- > [email protected]" > > > > >This is something that is in my long to-do list, I will try to get > >back > to this in couple weeks. > > >I think the way how you are dealing with it nowadays is the best way > >to > try to discover the CPU capabilities, better in this way than let the > users blind. > > >Best, > > Thanks Marcelo, > > > > It’s not exactly critical. I just saw another project using > vmx.initialized and it seemed a much cleaner way to determine support > by seeing if vmm loads rather than probing log files. I asked here > expecting someone to just say “yes if that’s 1 then the host will run > guests”, or “no you can’t tell if guests will run just by that sysctl”. > > > > Matt > > Could you share with me what project is using vmx.initialized? https://github.com/bigdragonsoft/bvm src/vm.c line 2790 > Best, -- _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to "[email protected]"
