From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752303AbeDKJYK (ORCPT ); Wed, 11 Apr 2018 05:24:10 -0400 Received: from smtp-fw-6001.amazon.com ([52.95.48.154]:33378 "EHLO smtp-fw-6001.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751734AbeDKJYI (ORCPT ); Wed, 11 Apr 2018 05:24:08 -0400 X-IronPort-AV: E=Sophos;i="5.48,435,1517875200"; d="scan'208";a="339348924" From: KarimAllah Ahmed To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: KarimAllah Ahmed , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , x86@kernel.org Subject: [PATCH] X86/KVM: Do not allow DISABLE_EXITS_MWAIT when LAPIC ARAT is not available Date: Wed, 11 Apr 2018 11:16:03 +0200 Message-Id: <1523438163-768-1-git-send-email-karahmed@amazon.de> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If the processor does not have an "Always Running APIC Timer" (aka ARAT), we should not give guests direct access to MWAIT. The LAPIC timer would stop ticking in deep C-states, so any host deadlines would not wakeup the host kernel. The host kernel intel_idle driver handles this by switching to broadcast mode when ARAT is not available and MWAIT is issued with a deep C-state that would stop the LAPIC timer. When MWAIT is passed through, we can not tell when MWAIT is issued. So just disable this capability when LAPIC ARAT is not available. I am not even sure if there are any CPUs with VMX support but no LAPIC ARAT or not. Cc: Paolo Bonzini Cc: Radim Krčmář Cc: Thomas Gleixner Cc: Ingo Molnar Cc: H. Peter Anvin Cc: x86@kernel.org Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Reported-by: Wanpeng Li Signed-off-by: KarimAllah Ahmed --- arch/x86/kvm/x86.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b2ff74b..0334b25 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2819,7 +2819,8 @@ static int msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs __user *user_msrs, static inline bool kvm_can_mwait_in_guest(void) { return boot_cpu_has(X86_FEATURE_MWAIT) && - !boot_cpu_has_bug(X86_BUG_MONITOR); + !boot_cpu_has_bug(X86_BUG_MONITOR) && + boot_cpu_has(X86_FEATURE_ARAT); } int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) -- 2.7.4