Re: [PATCH 1/3] kvm: arm/arm64: Take mmap_sem in stage2_unmap_vm

Christoffer Dall
2017-03-15T09:17:55Z

On Tue, Mar 14, 2017 at 02:52:32PM +0000, Suzuki K Poulose wrote:
> From: Marc Zyngier <marc.zyngier@arm.com>
>
> We don't hold the mmap_sem while searching for the VMAs when
> we try to unmap each memslot for a VM. Fix this properly to
> avoid unexpected results.
>
> Fixes: commit 957db105c997 ("arm/arm64: KVM: Introduce stage2_unmap_vm")
> Cc: stable@vger.kernel.org # v3.19+
> Cc: Christoffer Dall <christoffer.dall@linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> arch/arm/kvm/mmu.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 962616f..f2e2e0c 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -803,6 +803,7 @@ void stage2_unmap_vm(struct kvm *kvm)
> int idx;
>
> idx = srcu_read_lock(&kvm->srcu);
> + down_read(&current->mm->mmap_sem);
> spin_lock(&kvm->mmu_lock);
>
> slots = kvm_memslots(kvm);
> @@ -810,6 +811,7 @@ void stage2_unmap_vm(struct kvm *kvm)
> stage2_unmap_memslot(kvm, memslot);
>
> spin_unlock(&kvm->mmu_lock);
> + up_read(&current->mm->mmap_sem);
> srcu_read_unlock(&kvm->srcu, idx);
> }
>
> --
> 2.7.4
>

Are we sure that holding mmu_lock is valid while holding the mmap_sem?

Thanks,
-Christoffer