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KVM: MMU: Fix off-by-one calculating large page count

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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>
This commit is contained in:
Avi Kivity 2009-03-29 16:31:25 +03:00
parent 0910697403
commit 99894a799f
1 changed files with 3 additions and 5 deletions
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8
virt/kvm/kvm_main.c
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@ -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));