KVM: MMU: mark page table dirty when a pte is actually modified

Sometime cmpxchg_gpte doesn't modify gpte, in such case, don't mark
page table page as dirty.

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index c7f2777..5c8ac06 100644 (file)
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -177,10 +177,10 @@ walk:
                if (!(pte & PT_ACCESSED_MASK)) {
                        trace_kvm_mmu_set_accessed_bit(table_gfn, index,
                                                       sizeof(pte));
-                       mark_page_dirty(vcpu->kvm, table_gfn);
                        if (FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn,
                            index, pte, pte|PT_ACCESSED_MASK))
                                goto walk;
+                       mark_page_dirty(vcpu->kvm, table_gfn);
                        pte |= PT_ACCESSED_MASK;
                }
 
@@ -217,11 +217,11 @@ walk:
                bool ret;
 
                trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
-               mark_page_dirty(vcpu->kvm, table_gfn);
                ret = FNAME(cmpxchg_gpte)(vcpu->kvm, table_gfn, index, pte,
                            pte|PT_DIRTY_MASK);
                if (ret)
                        goto walk;
+               mark_page_dirty(vcpu->kvm, table_gfn);
                pte |= PT_DIRTY_MASK;
                walker->ptes[walker->level - 1] = pte;
        }