Re: [67/90] intel idle: Make idle driver more robust

[Kirill A. Shutemov]

On Mon, Jan 23, 2012 at 03:39:53PM -0800, Greg KH wrote:
> 3.0-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Thomas Renninger <trenn@xxxxxxx>
> 
> commit 5c2a9f06a9cd7194f884cdc88144866235dec07d upstream.
> 
> kvm -cpu host passes the original cpuid info to the guest.
> 
> Latest kvm version seem to return true for mwait_leaf cpuid
> function on recent Intel CPUs. But it does not return mwait
> C-states (mwait_substates), instead zero is returned.
> 
> While real CPUs seem to always return non-zero values, the intel
> idle driver should not get active in kvm (mwait_substates == 0)
> case and bail out.
> Otherwise a Null pointer exception will happen later when the
> cpuidle subsystem tries to get active:
> [0.984807] BUG: unable to handle kernel NULL pointer dereference at (null)
> [0.984807] IP: [<(null)>] (null)
> ...
> [0.984807][<ffffffff8143cf34>] ? cpuidle_idle_call+0xb4/0x340
> [0.984807][<ffffffff8159e7bc>] ? __atomic_notifier_call_chain+0x4c/0x70
> [0.984807][<ffffffff81001198>] ? cpu_idle+0x78/0xd0
> 
> Reference:
> https://bugzilla.novell.com/show_bug.cgi?id=726296
> 
> Signed-off-by: Thomas Renninger <trenn@xxxxxxx>
> CC: Bruno Friedmann <bruno@xxxxxxxxxxx>
> Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> 
> ---
>  drivers/idle/intel_idle.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -321,7 +321,8 @@ static int intel_idle_probe(void)
>  	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &mwait_substates);
>  
>  	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
> -		!(ecx & CPUID5_ECX_INTERRUPT_BREAK))
> +	    !(ecx & CPUID5_ECX_INTERRUPT_BREAK) ||
> +	    !mwait_substates)
>  			return -ENODEV;

It breaks build for me.