linux-kernel - Re: kernel bug in kvm

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Date:	Sun, 01 Nov 2009 11:45:36 +0100
From:	Tejun Heo <tj@...nel.org>
To:	Avi Kivity <avi@...hat.com>
CC:	Andrew Theurer <habanero@...ux.vnet.ibm.com>, kvm@...r.kernel.org,
	Linux-kernel@...r.kernel.org
Subject: Re: kernel bug in kvm_intel

Hello,

Avi Kivity wrote:
> We get a page fault immediately (next instruction) after returning from
> the guest when running with oprofile.  The page fault address does not
> match anything the instruction does, so presumably it is one of the
> accesses the processor performs in order to service an NMI (ordinary
> interrupts are masked; and the fact that it happens with oprofile
> strengthens this assumption).

Ah... okay, that's tricky but IIRC faults like that can be
distinguished from regular ones via processor state, right?

> If this is correct, the fault is not in the NMI handler itself, but in
> one of the memory areas the cpu looks in to vector the NMI, which can be:
> 
> - the IDT
> - the GDT
> - the TSS
> - the NMI stack
> 
> Except for the IDT these are per-cpu structure, though I don't know
> whether they are allocated with the percpu infrastructure.

Don't know where NMI stack is but all else are percpu.

> Here is the code in question:
> 
>>     3ae7:       75 05                   jne    3aee<vmx_vcpu_run+0x26a>
>>       3ae9:       0f 01 c2                vmlaunch
>>       3aec:       eb 03                   jmp    3af1<vmx_vcpu_run+0x26d>
>>       3aee:       0f 01 c3                vmresume
>>       3af1:       48 87 0c 24             xchg   %rcx,(%rsp)
> 
> ^^^ fault, but not at (%rsp)

Can you please post the full oops (including kernel debug messages
during boot) or give me a pointer to the original message?  Also, does
the faulting address coincide with any symbol?

Thanks.

-- 
tejun
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