From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [PATCH 3/3] kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd Date: Wed, 15 Mar 2017 11:56:39 +0100 Message-ID: <20170315105639.GA31974@cbox> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, andreyknvl@google.com, ard.biesheuvel@linaro.org, will.deacon@arm.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org, kcc@google.com, syzkaller@googlegroups.com, dvyukov@google.com, catalin.marinas@arm.com, pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu To: Marc Zyngier Return-path: Content-Disposition: inline In-Reply-To: <314fbde3-17e6-414b-85e6-326de22bdc1c@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu List-Id: kvm.vger.kernel.org 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 > >> --- > >> arch/arm/kvm/mmu.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c > >> index 13b9c1f..b361f71 100644 > >> --- a/arch/arm/kvm/mmu.c > >> +++ b/arch/arm/kvm/mmu.c > >> @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm) > >> if (kvm->arch.pgd == NULL) > >> return; > >> > >> + spin_lock(&kvm->mmu_lock); > >> unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE); > >> + spin_unlock(&kvm->mmu_lock); > >> + > > > > This ends up holding the spin lock for potentially quite a while, where > > we can do things like __flush_dcache_area(), which I think can fault. > > I believe we're always using the linear mapping (or kmap on 32bit) in > order not to fault. > 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? Thanks, -Christoffer