Re: [PATCH 3/3] kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd

Marc Zyngier
2017-03-15T09:39:26Z

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 <marc.zyngier@arm.com>
>> Cc: Christoffer Dall <christoffer.dall@linaro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> 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.

Thanks,

M.
--
Jazz is not dead. It just smells funny...