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

Greg KH
2009-05-06T21:57:23Z

[-- Attachment #1: kvm-mmu-fix-off-by-one-calculating-large-page-count.patch --]
[-- Type: text/plain, Size: 1415 bytes --]

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

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

From: Avi Kivity <avi@redhat.com>

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@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
---
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));