KVM: MMU: Add gpte_valid() helper

Move the code to check whether a gpte has changed since we fetched it into
a helper.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 17 insertions, 8 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 0c7461d3a5be..e1c1f9eb1cc1 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -299,6 +299,17 @@ static void FNAME(update_pte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
                      gpte_to_gfn(gpte), pfn, true, true);
 }
 
+static bool FNAME(gpte_changed)(struct kvm_vcpu *vcpu,
+                                struct guest_walker *gw, int level)
+{
+        int r;
+        pt_element_t curr_pte;
+
+        r = kvm_read_guest_atomic(vcpu->kvm, gw->pte_gpa[level - 1],
+                                  &curr_pte, sizeof(curr_pte));
+        return r || curr_pte != gw->ptes[level - 1];
+}
+
 /*
  * Fetch a shadow pte for a specific level in the paging hierarchy.
  */
@@ -312,11 +323,9 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
         u64 *sptep = NULL;
         int direct;
         gfn_t table_gfn;
-        int r;
         int level;
         bool dirty = is_dirty_gpte(gw->ptes[gw->level - 1]);
         unsigned direct_access;
-        pt_element_t curr_pte;
         struct kvm_shadow_walk_iterator iterator;
 
         if (!is_present_gpte(gw->ptes[gw->level - 1]))
@@ -365,17 +374,17 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                 }
                 sp = kvm_mmu_get_page(vcpu, table_gfn, addr, level-1,
                                                direct, access, sptep);
-                if (!direct) {
-                        r = kvm_read_guest_atomic(vcpu->kvm,
-                                                  gw->pte_gpa[level - 2],
-                                                  &curr_pte, sizeof(curr_pte));
-                        if (r || curr_pte != gw->ptes[level - 2]) {
+                if (!direct)
+                        /*
+                         * Verify that the gpte in the page we've just write
+                         * protected is still there.
+                         */
+                        if (FNAME(gpte_changed)(vcpu, gw, level - 1)) {
                                 kvm_mmu_put_page(sp, sptep);
                                 kvm_release_pfn_clean(pfn);
                                 sptep = NULL;
                                 break;
                         }
-                }
 
                 link_shadow_page(sptep, sp);
         }