[bug report] KVM: x86/mmu: Skip rmap operations if rmaps not allocated

[bug report] KVM: x86/mmu: Skip rmap operations if rmaps not allocated

[Dan Carpenter]

Hello Ben Gardon,

The patch e2209710ccc5: "KVM: x86/mmu: Skip rmap operations if rmaps
not allocated" from May 18, 2021, leads to the following static
checker warning:

	arch/x86/kvm/mmu/mmu.c:5704 kvm_mmu_zap_collapsible_sptes()
	error: uninitialized symbol 'flush'.

arch/x86/kvm/mmu/mmu.c
  5687  void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
  5688                                     const struct kvm_memory_slot *memslot)
  5689  {
  5690          /* FIXME: const-ify all uses of struct kvm_memory_slot.  */
  5691          struct kvm_memory_slot *slot = (struct kvm_memory_slot *)memslot;
  5692          bool flush;
                ^^^^^^^^^^
needs to be "bool flush = false;"

  5693  
  5694          if (kvm_memslots_have_rmaps(kvm)) {
  5695                  write_lock(&kvm->mmu_lock);
  5696                  flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
  5697                  if (flush)
  5698                          kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
  5699                  write_unlock(&kvm->mmu_lock);
  5700          }
  5701  
  5702          if (is_tdp_mmu_enabled(kvm)) {
  5703                  read_lock(&kvm->mmu_lock);
  5704                  flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, flush);
                                                                             ^^^^^
Unintialized.

  5705                  if (flush)
  5706                          kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
  5707                  read_unlock(&kvm->mmu_lock);
  5708          }
  5709  }

regards,
dan carpenter

Re: [bug report] KVM: x86/mmu: Skip rmap operations if rmaps not allocated

[Ben Gardon]

Hi Dan,

Thanks for reporting this. I believe it's already been fixed by "KVM:
x86/mmu: Fix uninitialized boolean variable flush" from Colin King.

On Fri, Jun 25, 2021 at 2:50 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> Hello Ben Gardon,
>
> The patch e2209710ccc5: "KVM: x86/mmu: Skip rmap operations if rmaps
> not allocated" from May 18, 2021, leads to the following static
> checker warning:
>
>         arch/x86/kvm/mmu/mmu.c:5704 kvm_mmu_zap_collapsible_sptes()
>         error: uninitialized symbol 'flush'.
>
> arch/x86/kvm/mmu/mmu.c
>   5687  void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>   5688                                     const struct kvm_memory_slot *memslot)
>   5689  {
>   5690          /* FIXME: const-ify all uses of struct kvm_memory_slot.  */
>   5691          struct kvm_memory_slot *slot = (struct kvm_memory_slot *)memslot;
>   5692          bool flush;
>                 ^^^^^^^^^^
> needs to be "bool flush = false;"
>
>   5693
>   5694          if (kvm_memslots_have_rmaps(kvm)) {
>   5695                  write_lock(&kvm->mmu_lock);
>   5696                  flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
>   5697                  if (flush)
>   5698                          kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
>   5699                  write_unlock(&kvm->mmu_lock);
>   5700          }
>   5701
>   5702          if (is_tdp_mmu_enabled(kvm)) {
>   5703                  read_lock(&kvm->mmu_lock);
>   5704                  flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, flush);
>                                                                              ^^^^^
> Unintialized.
>
>   5705                  if (flush)
>   5706                          kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
>   5707                  read_unlock(&kvm->mmu_lock);
>   5708          }
>   5709  }
>
> regards,
> dan carpenter