KVM: MMU: Use gfn_to_rmap() instead of directly reading rmap array

This helps to make rmap architecture specific in a later patch.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index a9a2052..ee768bb 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1181,7 +1181,8 @@
 	unsigned long *rmapp;
 
 	while (mask) {
-		rmapp = &slot->rmap[gfn_offset + __ffs(mask)];
+		rmapp = __gfn_to_rmap(slot->base_gfn + gfn_offset + __ffs(mask),
+				      PT_PAGE_TABLE_LEVEL, slot);
 		__rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL, false);
 
 		/* clear the first set bit */