From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-Id: <20120124023932.668116344@clark.kroah.org> Date: Mon, 23 Jan 2012 18:35:18 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Thomas Renninger , Bruno Friedmann , Len Brown Subject: [098/129] intel idle: Make idle driver more robust In-Reply-To: <20120124024041.GA18422@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ Content-Length: 1651 Lines: 47 From: Thomas Renninger 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][] ? cpuidle_idle_call+0xb4/0x340 [0.984807][] ? __atomic_notifier_call_chain+0x4c/0x70 [0.984807][] ? cpu_idle+0x78/0xd0 Reference: https://bugzilla.novell.com/show_bug.cgi?id=726296 Signed-off-by: Thomas Renninger CC: Bruno Friedmann Signed-off-by: Len Brown Signed-off-by: Greg Kroah-Hartman --- 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 @@ -348,7 +348,8 @@ 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; pr_debug(PREFIX "MWAIT substates: 0x%x\n", mwait_substates);