Hi Marc, On 15/03/17 13:43, Marc Zyngier wrote: > On 15/03/17 13:35, Christoffer Dall wrote: >> On Wed, Mar 15, 2017 at 01:28:07PM +0000, Marc Zyngier wrote: >>> On 15/03/17 10:56, Christoffer Dall wrote: >>>> 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@xxxxxxxxxxxxxxx # v3.10+ >>>>>>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx> >>>>>>> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx> >>>>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx> >>>>>>> --- >>>>>>> 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? >>> >>> That definitely rings a bell: stage2_wp_range() uses that kind of trick >>> to give the system a chance to breathe. Maybe we could use a similar >>> trick in our S2 unmapping code? How about this (completely untested) patch: >>> >>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c >>> index 962616fd4ddd..1786c24212d4 100644 >>> --- a/arch/arm/kvm/mmu.c >>> +++ b/arch/arm/kvm/mmu.c >>> @@ -292,8 +292,13 @@ static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size) >>> phys_addr_t addr = start, end = start + size; >>> phys_addr_t next; >>> >>> + BUG_ON(!spin_is_locked(&kvm->mmu_lock)); Nit: assert_spin_locked() is somewhat more pleasant (and currently looks to expand to the exact same code). Robin. >>> + >>> pgd = kvm->arch.pgd + stage2_pgd_index(addr); >>> do { >>> + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) >>> + cond_resched_lock(&kvm->mmu_lock); >>> + >>> next = stage2_pgd_addr_end(addr, end); >>> if (!stage2_pgd_none(*pgd)) >>> unmap_stage2_puds(kvm, pgd, addr, next); >>> >>> The additional BUG_ON() is just for my own peace of mind - we seem to >>> have missed a couple of these lately, and the "breathing" code makes >>> it imperative that this lock is being taken prior to entering the >>> function. >>> >> >> Looks good to me! > > OK. I'll stash that on top of Suzuki's series, and start running some > actual tests... ;-) > > Thanks, > > M. >