From 99894a799f09cf9e28296bb16e75bd5830fd2c4e Mon Sep 17 00:00:00 2001
From: Avi Kivity <avi@redhat.com>
Date: Sun, 29 Mar 2009 16:31:25 +0300
Subject: [PATCH] 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).
Cc: stable@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>
---
virt/kvm/kvm_main.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 605697e9c4dd5..28d693a1ee8ff 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -920,6 +920,7 @@ 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;
@@ -995,11 +996,8 @@ 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));
--
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