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

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Date:	Mon, 18 Oct 2010 21:58:13 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Avi Kivity <avi@...hat.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 Mon, Oct 18, 2010 at 03:50:15PM +0200, Avi Kivity wrote:
>  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).

It's 0
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