From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933529AbcHDMUJ (ORCPT ); Thu, 4 Aug 2016 08:20:09 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:36168 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933297AbcHDMUG (ORCPT ); Thu, 4 Aug 2016 08:20:06 -0400 Subject: Re: [PATCH 1/2] KVM: lapic: fix access preemption timer stuff even if kernel_irqchip=off To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1470197053-3581-1-git-send-email-wanpeng.li@hotmail.com> Cc: Wanpeng Li , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Yunhong Jiang From: Paolo Bonzini Message-ID: <1b93d6f6-855f-271b-dcf6-d322e2fe9f13@redhat.com> Date: Thu, 4 Aug 2016 14:20:02 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 MIME-Version: 1.0 In-Reply-To: <1470197053-3581-1-git-send-email-wanpeng.li@hotmail.com> 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 On 03/08/2016 06:04, Wanpeng Li wrote: > From: Wanpeng Li > > BUG: unable to handle kernel NULL pointer dereference at 000000000000008c > IP: [] kvm_lapic_hv_timer_in_use+0x10/0x20 [kvm] > PGD 0 > Oops: 0000 [#1] SMP > Call Trace: > kvm_arch_vcpu_load+0x86/0x260 [kvm] > vcpu_load+0x46/0x60 [kvm] > kvm_vcpu_ioctl+0x79/0x7c0 [kvm] > ? __lock_is_held+0x54/0x70 > do_vfs_ioctl+0x96/0x6a0 > ? __fget_light+0x2a/0x90 > SyS_ioctl+0x79/0x90 > do_syscall_64+0x7c/0x1e0 > entry_SYSCALL64_slow_path+0x25/0x25 > RIP [] kvm_lapic_hv_timer_in_use+0x10/0x20 [kvm] > RSP > CR2: 000000000000008c > ---[ end trace a55fb79d2b3b4ee8 ]--- > > This can be reproduced steadily by kernel_irqchip=off. > > We should not access preemption timer stuff if lapic is emulated in userspace. > This patch fix it by avoiding access preemption timer stuff when kernel_irqchip=off. > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Yunhong Jiang > Signed-off-by: Wanpeng Li > --- > arch/x86/kvm/lapic.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 6895fd2..0120a58 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1348,6 +1348,9 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic) > > bool kvm_lapic_hv_timer_in_use(struct kvm_vcpu *vcpu) > { > + if (!lapic_in_kernel(vcpu)) > + return false; > + > return vcpu->arch.apic->lapic_timer.hv_timer_in_use; > } > EXPORT_SYMBOL_GPL(kvm_lapic_hv_timer_in_use); > Applied patch 1, while 2 will wait for 4.9. Paolo