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SubjectGuest kernel hangs in smp kvm for older kernels prior to tsc sync cleanup
Booting RHEL 5 i386 in kvm with -no-kvm-irqchip -smp 4 will hang in 
udev. I bisected this to a change in the _guest_ kernel:

> commit 95492e4646e5de8b43d9a7908d6177fb737b61f0
> Author: Ingo Molnar <mingo@elte.hu>
> Date: Fri Feb 16 01:27:34 2007 -0800
>
> [PATCH] x86: rewrite SMP TSC sync code
>
> make the TSC synchronization code more robust, and unify it
> between x86_64 and
> i386.
>
> The biggest change is the removal of the 'fix up TSCs' code on
> x86_64 and
> i386, in some rare cases it was /causing/ time-warps on SMP systems.
>
> The new code only checks for TSC asynchronity - and if it can prove a
> time-warp (if it can observe the TSC going backwards when going
> from one CPU
> to another within a critical section), then the TSC clock-source
> is turned
> off.
>
> The TSC synchronization-checking code also got moved into a
> separate file.

So, guest kernels prior to this commit will hang in kvm smp; after this
commit they will boot fine.

While the change mentions that it fixes a time warp bug, it also says it
should be rare. So clearly kvm smp tsc handing is buggy. Ingo/Thomas,
(or anybody else), do you have any insight as to what kvm can be doing
wrong to trigger this behavior?


--
error compiling committee.c: too many arguments to function



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