On Oct 27, 2014, at 10:54 AM, John Baldwin <j...@freebsd.org> wrote:
> On Friday, October 17, 2014 01:20:50 PM Warner Losh wrote: >> Author: imp >> Date: Fri Oct 17 13:20:49 2014 >> New Revision: 273214 >> URL: https://svnweb.freebsd.org/changeset/base/273214 >> >> Log: >> Fix build to not bogusly always rebuild vmm.ko. >> >> Rename vmx_assym.s to vmx_assym.h to reflect that file's actual use >> and update vmx_support.S's include to match. Add vmx_assym.h to the >> SRCS to that it gets properly added to the dependency list. Add >> vmx_support.S to SRCS as well, so it gets built and needs fewer >> special-case goo. Remove now-redundant special-case goo. Finally, >> vmx_genassym.o doesn't need to depend on a hand expanded ${_ILINKS} >> explicitly, that's all taken care of by beforedepend. >> >> With these items fixed, we no longer build vmm.ko every single time >> through the modules on a KERNFAST build. > > So I cheered for this before, but it appears to be broken. :( > > Namely, I rebuilt world + kernel on my laptop this weekend (it was about a > month old). My normal setup builds kernels with NO_KERNELCLEAN=yes. On my > next reboot when I started a bhyve VM I promptly got a panic due to a page > fault in this assembly code: > > /* > * If 'vmx->eptgen[curcpu]' is not identical to 'pmap->pm_eptgen' > * then we must invalidate all mappings associated with this EPTP. > */ > movq PM_EPTGEN(%r11), %r10 > cmpq %r10, VMX_EPTGEN(%rsi, %rax, 8) > je guest_restore > > (The 'cmpq' instruction) > > This change came to mind, so I blew away the 'vmm' module directory and > rebuilt my kernel. Comparing the assembly of this instruction before and > after used different values for VMX_EPTGEN. In other words, the > NO_KERNELCLEAN=yes build failed to regenerate vmx_assym.h and the build used > stale values. Is there a way to force this condition for testing? > In particular, if you examine the generated .depend file, you will find that > there are no dependencies recorded for vmx_genassym.o, so it is never rebuilt > if any of the headers it includes are changed. In my case the panic happened > to be one that was easily diagnosed, but I could imagine stale assym headers > causing very odd crashes that would be quite hard to track down. I think > these changes should be reverted if we can't fix the dependencies of the > associated object files they are generated from. :( Give me a bit and I’ll fix it. There’s a number of implicit dependencies that don’t get recorded in the .depend file, iirc, so that’s not completely conclusive. Not building, though is kinda a big hint that something’s amiss. However, -DNO_CLEAN has always been a very-sharp edged tool that will cut you in a number of ways, so there’s no rush to back this out. Warner
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