From a42fe5f79f3fe3a2f4ca72e746eb62613f6e811e Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@redhat.com>
Date: Sun, 29 Mar 2009 16:31:25 +0300
Subject: [PATCH 5/6] KVM: MMU: Fix off-by-one calculating large page count

The large page initialization code concludes there are two large pages spanned
by a slot covering 1 (small) page starting at gfn 1.  This is incorrect, and
also results in incorrect write_count initialization in some cases (base = 1,
npages = 513 for example).

(cherry picked from commit 54d4f4cd1c334c8a1eece613895cb86370ca7107)

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
RH-Upstream-status: applied(kvm/queue)
Bugzilla: 500263
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: john cooper <john.cooper@redhat.com>
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Avi Kivity <avi@redhat.com>
---
 virt/kvm/kvm_main.c |    8 +++-----
 1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 19140f7..68e5b2d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -956,6 +956,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
 	int r;
 	gfn_t base_gfn;
 	unsigned long npages;
+	int largepages;
 	unsigned long i;
 	struct kvm_memory_slot *memslot;
 	struct kvm_memory_slot old, new;
@@ -1031,11 +1032,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
 			new.userspace_addr = 0;
 	}
 	if (npages && !new.lpage_info) {
-		int largepages = npages / KVM_PAGES_PER_HPAGE;
-		if (npages % KVM_PAGES_PER_HPAGE)
-			largepages++;
-		if (base_gfn % KVM_PAGES_PER_HPAGE)
-			largepages++;
+		largepages = 1 + (base_gfn + npages - 1) / KVM_PAGES_PER_HPAGE;
+		largepages -= base_gfn / KVM_PAGES_PER_HPAGE;
 
 		new.lpage_info = vmalloc(largepages * sizeof(*new.lpage_info));
 
-- 
1.6.3.rc4.29.g8146