From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: Disable irq while unregistering user notifier Date: Wed, 2 Nov 2016 18:25:25 +0100 Message-ID: <61b5a6c3-9a30-feef-869b-bf9251454381@redhat.com> References: <1477087712-175064-1-git-send-email-ikalvarado@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , David Matlack To: Ignacio Alvarado , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60460 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932624AbcKBRZ3 (ORCPT ); Wed, 2 Nov 2016 13:25:29 -0400 In-Reply-To: <1477087712-175064-1-git-send-email-ikalvarado@google.com> Sender: kvm-owner@vger.kernel.org List-ID: On 22/10/2016 00:08, 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 Should drop_user_return_notifiers instead be moved to kvm_arch_exit? Thanks, Paolo > --- > arch/x86/kvm/x86.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index e375235..51f87f0 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -210,7 +210,15 @@ 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) > + goto out; > for (slot = 0; slot < shared_msrs_global.nr; ++slot) { > values = &locals->values[slot]; > if (values->host != values->curr) { > @@ -220,6 +228,8 @@ static void kvm_on_user_return(struct user_return_notifier *urn) > } > locals->registered = false; > user_return_notifier_unregister(urn); > +out: > + local_irq_restore(flags); > } > > static void shared_msr_update(unsigned slot, u32 msr) >