Messages in this thread | | | Date | Mon, 3 Jul 2017 10:03:13 +0200 | From | Christoffer Dall <> | Subject | Re: [PATCH] KVM: arm/arm64: Handle hva aging while destroying the vm |
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Hi Alex,
On Fri, Jun 23, 2017 at 05:21:59PM +0200, Alexander Graf wrote: > If we want to age an HVA while the VM is getting destroyed, we have a > tiny race window during which we may end up dereferencing an invalid > kvm->arch.pgd value. > > CPU0 CPU1 > > kvm_age_hva() > kvm_mmu_notifier_release() > kvm_arch_flush_shadow_all() > kvm_free_stage2_pgd() > <grab mmu_lock> > stage2_get_pmd() > <wait for mmu_lock> > set kvm->arch.pgd = 0 > <free mmu_lock> > <grab mmu_lock> > stage2_get_pud() > <access kvm->arch.pgd> > <use incorrect value>
I don't think this sequence, can happen, but I think kvm_age_hva() can be called with the mmu_lock held and kvm->pgd already being NULL.
Is that possible for the mmu notifiers to be calling clear(_flush)_young while also calling notifier_release?
If so, the patch below looks good to me.
Thanks, -Christoffer
> > This patch adds a check for that case. > > Signed-off-by: Alexander Graf <agraf@suse.de> > --- > virt/kvm/arm/mmu.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c > index f2d5b6c..227931f 100644 > --- a/virt/kvm/arm/mmu.c > +++ b/virt/kvm/arm/mmu.c > @@ -861,6 +861,10 @@ static pud_t *stage2_get_pud(struct kvm *kvm, struct kvm_mmu_memory_cache *cache > pgd_t *pgd; > pud_t *pud; > > + /* Do we clash with kvm_free_stage2_pgd()? */ > + if (!kvm->arch.pgd) > + return NULL; > + > pgd = kvm->arch.pgd + stage2_pgd_index(addr); > if (WARN_ON(stage2_pgd_none(*pgd))) { > if (!cache) > -- > 1.8.5.6 > > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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