Re: kernel panic caused by virtualbox(?)

On Mon, Aug 08, 2016 at 04:44:20PM -0700, Don Lewis wrote:
> On  8 Aug, Konstantin Belousov wrote:
> > On Mon, Aug 08, 2016 at 10:22:44AM -0700, John Baldwin wrote:
> >> On Thursday, August 04, 2016 05:10:29 PM Don Lewis wrote:
> >> > Reposted to -current to get some more eyes on this ...
> >> > 
> >> > I just got a kernel panic when I started up a CentOS 7 VM in virtualbox.
> >> > The host is:
> >> > 	FreeBSD 12.0-CURRENT #17 r302500 GENERIC amd64
> >> > The virtualbox version is:
> >> > 	virtualbox-ose-5.0.26
> >> > 	virtualbox-ose-kmod-5.0.26_1
> >> > 
> >> > The panic message is:
> >> > 
> >> > panic: Unregistered use of FPU in kernel
> >> > cpuid = 1
> >> > KDB: stack backtrace:
> >> > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe085a55d030
> >> > vpanic() at vpanic+0x182/frame 0xfffffe085a55d0b0
> >> > kassert_panic() at kassert_panic+0x126/frame 0xfffffe085a55d120
> >> > trap() at trap+0x7ae/frame 0xfffffe085a55d330
> >> > calltrap() at calltrap+0x8/frame 0xfffffe085a55d330
> >> > --- trap 0x16, rip = 0xffffffff827dd3a9, rsp = 0xfffffe085a55d408, rbp = 0xfffffe085a55d430 ---
> >> > g_pLogger() at 0xffffffff827dd3a9/frame 0xfffffe085a55d430
> >> > g_pLogger() at 0xffffffff8274e5c7/frame 0x3
> >> > KDB: enter: panic
> >> > 
> >> > Since g_pLogger is a symbol in vboxdrv.ko, it looks like virtualbox is
> >> > the trigger.
> >> > 
> >> > There are no symbols for the virtualbox kmods, possibly because I
> >> > installed them as an upgrade using packages (built with the same source
> >> > tree version) instead of by using PORTS_MODULES in make.conf, so ports
> >> > kgdb didn't have anything useful to say about what happened before the
> >> > trap.
> >> > 
> >> > This panic is very repeatable.  I just got another one when starting the
> >> > same VM., but this time the two calls before the trap were
> >> > null_bug_bypass().  Hmn, that symbol is in nullfs ...
> >> > 
> >> > I don't see this with a Windows 7 VM.
> >> > 
> >> > All of the virtualbox kmod files are compiled with -mno-mmx -mno-sse
> >> > -msoft-float -mno-aes -mno-avx
> > Your disassemble listed fxrstor instruction that failing, or did I
> > mis-remembered ? This is most likely some context switch code, either
> > by virtual machine or erronously executed guest code. It is not a
> > spontaneous use of FPU, but more likely something different. Can you
> > confirm ?
> > 
> > In either case, I do not remember any KBI changes around PCB layout or
> > fpu_enter() KPI recently.
> > 
> >> 
> >> I suspect head packages are quite likely built against the a "wrong" KBI
> >> and are too fragile to use for kmods vs compiling from ports. :-/  I would
> >> try a built-from-ports kmod to see if the panics go away.
> > 
> > FWIW, I will commit the following change shortly. Since third-party
> > modules break the invariant, either due to bugs (ndis wrappers) or
> > possibly due to KBI breakage, it is worth to have the detection enabled
> > for production kernels.
> 
> Interesting ... I tried running virtualbox on recent 10.3-STABLE with a
> GENERIC kernel and the guest seemed to operate properly.  Then I enabled
> INVARIANTS and got the panic.  I suspect that is why nobody has stumbled
> across this before.
> 
This is yet another reason to promote KASSERT to the full panic.
I expect that the vbox source lacks fpu_kern_enter() calls around the
FPU state restoration.