From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:47402 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933810AbcKQRbm (ORCPT ); Thu, 17 Nov 2016 12:31:42 -0500 Subject: Re: [PATCH v2] KVM: Disable irq while unregistering user notifier To: Ignacio Alvarado , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" References: <1478286955-108360-1-git-send-email-ikalvarado@google.com> Cc: kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , David Matlack , stable From: Paolo Bonzini Message-ID: Date: Thu, 17 Nov 2016 13:42:43 +0100 MIME-Version: 1.0 In-Reply-To: <1478286955-108360-1-git-send-email-ikalvarado@google.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org List-ID: On 04/11/2016 20:15, Ignacio Alvarado wrote: > Function user_notifier_unregister should be called only once for each > registered user notifier. > > Function kvm_arch_hardware_disable can be executed from an IPI context > which could cause a race condition with a VCPU returning to user mode > and attempting to unregister the notifier. > > Signed-off-by: Ignacio Alvarado Cc: stable@vger.kernel.org Reviewed-by: Paolo Bonzini > --- > Changelog since v1: > - Move unregistration to the beginning of kvm_on_user_return > > arch/x86/kvm/x86.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index e375235..952e19d 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -210,7 +210,18 @@ static void kvm_on_user_return(struct user_return_notifier *urn) > struct kvm_shared_msrs *locals > = container_of(urn, struct kvm_shared_msrs, urn); > struct kvm_shared_msr_values *values; > + unsigned long flags; > > + /* > + * Disabling irqs at this point since the following code could be > + * interrupted and executed through kvm_arch_hardware_disable() > + */ > + local_irq_save(flags); > + if (locals->registered) { > + locals->registered = false; > + user_return_notifier_unregister(urn); > + } > + local_irq_restore(flags); > for (slot = 0; slot < shared_msrs_global.nr; ++slot) { > values = &locals->values[slot]; > if (values->host != values->curr) { > @@ -218,8 +229,6 @@ static void kvm_on_user_return(struct user_return_notifier *urn) > values->curr = values->host; > } > } > - locals->registered = false; > - user_return_notifier_unregister(urn); > } > > static void shared_msr_update(unsigned slot, u32 msr) >