linux-kernel - Re: [BUG] kvm: guest can not startup due to triple fault

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Message-ID: <4CBC5097.1020105@redhat.com>
Date:	Mon, 18 Oct 2010 15:50:15 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Dave Young <hidave.darkstar@...il.com>
CC:	Jan Kiszka <jan.kiszka@....de>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] kvm: guest can not startup due to triple fault

  On 10/18/2010 03:46 PM, Avi Kivity wrote:
>  On 10/18/2010 03:45 PM, Dave Young wrote:
>> On Mon, Oct 18, 2010 at 03:26:30PM +0200, Avi Kivity wrote:
>> >   On 10/18/2010 02:58 PM, Dave Young wrote:
>> > >>
>> > >>   It's secondary_startup_64 enabling efer.sce and efer.nx.
>> > >>
>> > >>   Dave, please post your /proc/cpuinfo.  Is your host running 
>> with NX
>> > >>   disabled?
>> > >
>> > >I see nx bit in /proc/cpuinfo, Actually I don't know how to 
>> disable it.
>> >
>> >  Strange.
>> >
>> >  Please patch arch/x86/kvm/x86.c to printk efer_reserved_bits (a
>> >  global), efer (an argument) and old_efer (a local), and post the
>> >  results.
>>
>> I add printk before kvm_mmu_reset_context(vcpu), correct? get 
>> following value:
>>
>
> Add it at the beginning please, otherwise we'll miss the important one 
> due to an early return.
>

No need actually:

> [ 3228.468325] efer_reserved_bits = 0xfffffffffffffafe


Bit 11 is reserved, so the guest can't enable nx.

 From arch/x86/kvm/vmx.c:
> static __init int hardware_setup(void)
> {
>     if (setup_vmcs_config(&vmcs_config) < 0)
>         return -EIO;
>
>     if (boot_cpu_has(X86_FEATURE_NX))
>         kvm_enable_efer_bits(EFER_NX);
>

Please patch hardware_setup() to show the value of 
boot_cpu_has(X86_FEATURE_NX).

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

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