From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ignacio Alvarado Subject: Re: [PATCH] KVM: Disable irq while unregistering user notifier Date: Thu, 3 Nov 2016 15:26:19 -0700 Message-ID: References: <1477087712-175064-1-git-send-email-ikalvarado@google.com> <61b5a6c3-9a30-feef-869b-bf9251454381@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , kvm@vger.kernel.org, =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , David Matlack To: Paolo Bonzini Return-path: Received: from mail-oi0-f47.google.com ([209.85.218.47]:35150 "EHLO mail-oi0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932602AbcKCW0U (ORCPT ); Thu, 3 Nov 2016 18:26:20 -0400 Received: by mail-oi0-f47.google.com with SMTP id x4so114590764oix.2 for ; Thu, 03 Nov 2016 15:26:20 -0700 (PDT) In-Reply-To: <61b5a6c3-9a30-feef-869b-bf9251454381@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: The risk would still be present since fire_user_return_notifiers could potentially run at any time and kvm_on_user return could be called from drop_user_return_notifiers either from the kvm_put_kvm path or the kvm_arch_exit path. Regards On Wed, Nov 2, 2016 at 10:25 AM, Paolo Bonzini wrote: > > > 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) >> -- Ignacio Alvarado