KVM: PPC: Book3S HV: Always flush TLB in kvmppc_alloc_reset_hpt()

The KVM_PPC_ALLOCATE_HTAB ioctl(), implemented by kvmppc_alloc_reset_hpt()
is supposed to completely clear and reset a guest's Hashed Page Table (HPT)
allocating or re-allocating it if necessary.

In the case where an HPT of the right size already exists and it just
zeroes it, it forces a TLB flush on all guest CPUs, to remove any stale TLB
entries loaded from the old HPT.

However, that situation can arise when the HPT is resizing as well - or
even when switching from an RPT to HPT - so those cases need a TLB flush as
well.

So, move the TLB flush to trigger in all cases except for errors.

Cc: stable@vger.kernel.org # v4.10+
Fixes: f98a8bf9ee ("KVM: PPC: Book3S HV: Allow KVM_PPC_ALLOCATE_HTAB ioctl() to change HPT size")
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -165,8 +165,6 @@ long kvmppc_alloc_reset_hpt(struct kvm *kvm, int order)
 		 * Reset all the reverse-mapping chains for all memslots
 		 */
 		kvmppc_rmap_reset(kvm);
-		/* Ensure that each vcpu will flush its TLB on next entry. */
-		cpumask_setall(&kvm->arch.need_tlb_flush);
 		err = 0;
 		goto out;
 	}
@@ -182,6 +180,10 @@ long kvmppc_alloc_reset_hpt(struct kvm *kvm, int order)
 	kvmppc_set_hpt(kvm, &info);
 
 out:
+	if (err == 0)
+		/* Ensure that each vcpu will flush its TLB on next entry. */
+		cpumask_setall(&kvm->arch.need_tlb_flush);
+
 	mutex_unlock(&kvm->lock);
 	return err;
 }