On 08/08/2011 12:55 PM, Tejun Heo wrote:
Hello, Avi. On Sun, Aug 07, 2011 at 06:32:35PM +0300, Avi Kivity wrote: > qemu, under some conditions (-cpu host or -cpu kvm64), erroneously > passes family=15 as the virtual cpuid. This causes a BUG() in > percpu code during late boot: > > ------------[ cut here ]------------ > kernel BUG at mm/percpu.c:577!
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> All this applies to v3.0; current upstream (c2f340a69ca) fails even > worse, haven't yet determined exactly why. > > I'm surprised this hasn't been reported before; Ingo, don't you have > family=15 hosts in your test farm? Hmmm... I can't trigger the problem w/ kvm64 (I tried mounting and unmounting filesystems but it worked okay) and am quite skeptical this is a wide spread problem given that the percpu core code is used very widely and hasn't seen a lot of changes lately. Is there anything specific you need to do to trigger the condition? Can you try to print out the s_files addresses being allocated and freed?
Coming back to this, the trigger if cpuid family=6 and model>=13 (model 12 works). Looks like the code disables rep_good is some MSR doesn't have the expected value. While we should configure the MSR correctly, it looks like the fallback code for !rep_good is broken. Will look further.
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