Subject: fix kvm mmu notifier invalidate handler for huge spte

From: Andrea Arcangeli <aarcange@redhat.com>

The index wasn't calucalted correctly for huge spte so KVM guest was unstable
with transparent hugepages. This bug slipped under my eyes several times...
well hidden.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -809,8 +810,12 @@ static int kvm_handle_hva(struct kvm *kv
 			ret = handler(kvm, &memslot->rmap[gfn_offset], data);
 
 			for (j = 0; j < KVM_NR_PAGE_SIZES - 1; ++j) {
-				int idx = gfn_offset;
-				idx /= KVM_PAGES_PER_HPAGE(PT_DIRECTORY_LEVEL + j);
+				unsigned long idx;
+				int nr;
+
+				nr = KVM_PAGES_PER_HPAGE(PT_DIRECTORY_LEVEL+j);
+				idx = (memslot->base_gfn+gfn_offset) / nr -
+					memslot->base_gfn / nr;
 				ret |= handler(kvm,
 					&memslot->lpage_info[j][idx].rmap_pde,
 					data);