[patch 08/58] KVM: MMU: Fix off-by-one calculating large page count

[Greg KH]

2.6.29-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Avi Kivity <avi@xxxxxxxxxx>

upstream commit: 99894a799f09cf9e28296bb16e75bd5830fd2c4e

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).

Cc: stable@xxxxxxxxxx
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
---
 virt/kvm/kvm_main.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -964,6 +964,7 @@ int __kvm_set_memory_region(struct 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;
@@ -1039,11 +1040,8 @@ int __kvm_set_memory_region(struct 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));
 


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