From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757076AbbIUPmS (ORCPT ); Mon, 21 Sep 2015 11:42:18 -0400 Received: from mail.skyhub.de ([78.46.96.112]:47262 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756413AbbIUPmQ (ORCPT ); Mon, 21 Sep 2015 11:42:16 -0400 Date: Mon, 21 Sep 2015 17:42:13 +0200 From: Borislav Petkov To: Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v2] KVM: x86: put vcpu_create under kvm->srcu critical section Message-ID: <20150921154213.GA3666@pd.tnic> References: <1442815376-28641-1-git-send-email-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1442815376-28641-1-git-send-email-pbonzini@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 21, 2015 at 08:02:56AM +0200, Paolo Bonzini wrote: > This is needed in case vcpu_create wants to access the memslots array. > Fixes this lockdep splat: > > [26421.303750] =============================== > [26421.307952] [ INFO: suspicious RCU usage. ] > [26421.312161] 4.3.0-rc1+ #1 Not tainted > [26421.312161] ------------------------------- > [26421.312162] include/linux/kvm_host.h:488 suspicious rcu_dereference_check() usage! > [26421.312163] > other info that might help us debug this: > > [26421.312164] > rcu_scheduler_active = 1, debug_locks = 0 > [26421.312165] 1 lock held by qemu-system-i38/17000: > [26421.312189] #0: (&(&kvm->mmu_lock)->rlock){+.+...}, at: [] kvm_zap_gfn_range+0x24/0x1a0 [kvm] > [26421.312189] > stack backtrace: > [26421.312191] CPU: 3 PID: 17000 Comm: qemu-system-i38 Not tainted 4.3.0-rc1+ #1 > [26421.312192] Hardware name: To be filled by O.E.M. To be filled by O.E.M./M5A97 EVO R2.0, BIOS 1503 01/16/2013 > [26421.312195] 0000000000000001 ffff880386c0fc90 ffffffff812c8c2a ffff880423f0c740 > [26421.312197] ffff880386c0fcc0 ffffffff8109e60d ffff880429ff8000 ffffffffffffffff > [26421.312199] ffff880386844000 ffff880000000000 ffff880386c0fd30 ffffffffa02d6c18 > [26421.312199] Call Trace: > [26421.312205] [] dump_stack+0x4e/0x84 > [26421.312208] [] lockdep_rcu_suspicious+0xfd/0x130 > [26421.312223] [] kvm_zap_gfn_range+0x188/0x1a0 [kvm] > [26421.312235] [] kvm_set_cr0+0xde/0x1e0 [kvm] > [26421.312244] [] init_vmcb+0x760/0xad0 [kvm_amd] > [26421.312246] [] svm_create_vcpu+0x197/0x250 [kvm_amd] > [26421.312259] [] kvm_arch_vcpu_create+0x47/0x70 [kvm] > [26421.312268] [] kvm_vm_ioctl+0x302/0x7e0 [kvm] > [26421.312271] [] ? __lock_is_held+0x51/0x70 > [26421.312273] [] ? __fget+0x101/0x210 > [26421.312276] [] do_vfs_ioctl+0x2f4/0x560 > [26421.312277] [] ? __fget_light+0x29/0x90 > [26421.312279] [] SyS_ioctl+0x4c/0x90 > [26421.312282] [] entry_SYSCALL_64_fastpath+0x16/0x73 You probably want to trim away all those numbers (timestamps and call trace VAs) as they're useless. > Reported-by: Borislav Petkov > Signed-off-by: Paolo Bonzini > --- > arch/x86/kvm/x86.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 991466bf8dee..6107e09fc5b6 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -7064,13 +7064,16 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, > unsigned int id) > { > struct kvm_vcpu *vcpu; > + int idx; > > if (check_tsc_unstable() && atomic_read(&kvm->online_vcpus) != 0) > printk_once(KERN_WARNING > "kvm: SMP vm created on host with unstable TSC; " > "guest TSC will not be reliable\n"); > > + idx = srcu_read_lock(&kvm->srcu); > vcpu = kvm_x86_ops->vcpu_create(kvm, id); > + srcu_read_unlock(&kvm->srcu, idx); > > return vcpu; Other than that, it works. Tested-by: Borislav Petkov Thanks. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.