On 15/03/17 09:17, Christoffer Dall wrote:
> On Tue, Mar 14, 2017 at 02:52:32PM +0000, Suzuki K Poulose wrote:
>> From: Marc Zyngier <marc.zyngier@xxxxxxx>
>>
>> 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@xxxxxxxxxxxxxxx # v3.19+
>> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>> ---
>> 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(¤t->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(¤t->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?
Maybe I'm just confused by the many levels of locking, Here's my rational:
- kvm->srcu protects the memslot list
- mmap_sem protects the kernel VMA list
- mmu_lock protects the stage2 page tables (at least here)
I don't immediately see any issue with holding the mmap_sem mutex here
(unless there is a path that would retrigger a down operation on the
mmap_sem?).
Or am I missing something obvious?
Thanks,
M.
--
Jazz is not dead. It just smells funny...