Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753982AbdCOOdv (ORCPT ); Wed, 15 Mar 2017 10:33:51 -0400 Received: from foss.arm.com ([217.140.101.70]:47936 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751280AbdCOOdh (ORCPT ); Wed, 15 Mar 2017 10:33:37 -0400 Subject: Re: [PATCH 3/3] kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd To: Marc Zyngier , Christoffer Dall References: <1489503154-20705-1-git-send-email-suzuki.poulose@arm.com> <1489503154-20705-4-git-send-email-suzuki.poulose@arm.com> <20170315092147.GM1277@cbox> <314fbde3-17e6-414b-85e6-326de22bdc1c@arm.com> <20170315105639.GA31974@cbox> <0e5ff7f7-855c-ea28-fdee-73c062c3d289@arm.com> Cc: linux-arm-kernel@lists.infradead.org, andreyknvl@google.com, dvyukov@google.com, christoffer.dall@linaro.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kcc@google.com, syzkaller@googlegroups.com, will.deacon@arm.com, catalin.marinas@arm.com, pbonzini@redhat.com, mark.rutland@arm.com, ard.biesheuvel@linaro.org, stable@vger.kernel.org From: Suzuki K Poulose Message-ID: <0afc4248-9a1b-ee0f-8f9b-5357707b9d72@arm.com> Date: Wed, 15 Mar 2017 14:33:31 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 MIME-Version: 1.0 In-Reply-To: <0e5ff7f7-855c-ea28-fdee-73c062c3d289@arm.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2246 Lines: 58 On 15/03/17 13:28, Marc Zyngier wrote: > On 15/03/17 10:56, Christoffer Dall wrote: >> On Wed, Mar 15, 2017 at 09:39:26AM +0000, Marc Zyngier wrote: >>> On 15/03/17 09:21, Christoffer Dall wrote: >>>> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote: >>>>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling >>>>> unmap_stage2_range() on the entire memory range for the guest. This could >>>>> cause problems with other callers (e.g, munmap on a memslot) trying to >>>>> unmap a range. >>>>> >>>>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup") >>>>> Cc: stable@vger.kernel.org # v3.10+ >>>>> Cc: Marc Zyngier >>>>> Cc: Christoffer Dall >>>>> Signed-off-by: Suzuki K Poulose ... >> ok, then there's just the concern that we may be holding a spinlock for >> a very long time. I seem to recall Mario once added something where he >> unlocked and gave a chance to schedule something else for each PUD or >> something like that, because he ran into the issue during migration. Am >> I confusing this with something else? > > That definitely rings a bell: stage2_wp_range() uses that kind of trick > to give the system a chance to breathe. Maybe we could use a similar > trick in our S2 unmapping code? How about this (completely untested) patch: > > diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > index 962616fd4ddd..1786c24212d4 100644 > --- a/arch/arm/kvm/mmu.c > +++ b/arch/arm/kvm/mmu.c > @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) > phys_addr_t addr = start, end = start + size; > phys_addr_t next; > > + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); > + > pgd = kvm->arch.pgd + stage2_pgd_index(addr); > do { > + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) > + cond_resched_lock(&kvm->mmu_lock); nit: I think we could make the cond_resched_lock() unconditionally here: Given, __cond_resched_lock() already does all the above checks : kernel/sched/core.c: int __cond_resched_lock(spinlock_t *lock) { int resched = should_resched(PREEMPT_LOCK_OFFSET); ... if (spin_needbreak(lock) || resched) { Suzuki