From: Avi Kivity <a...@redhat.com>

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: sta...@kernel.org
Signed-off-by: Avi Kivity <a...@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 8aa3b95..363af32 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1076,6 +1076,7 @@ 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;
@@ -1151,11 +1152,8 @@ 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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