svn commit: r273214 - in head/sys: amd64/vmm/intel modules/vmm

[Warner Losh]

On Oct 27, 2014, at 10:54 AM, John Baldwin <jhb at 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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