KVM: MMU: Introduce drop_spte()

When we call rmap_remove(), we (almost) always immediately follow it by
an __set_spte() to a nonpresent pte.  Since we need to perform the two
operations atomically, to avoid losing the dirty and accessed bits, introduce
a helper drop_spte() and convert all call sites.

The operation is still nonatomic at this point.

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

1 files changed, 6 insertions, 7 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 59e750c1a269..796a325c7e59 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -353,8 +353,7 @@ static u64 *FNAME(fetch)(struct kvm_vcpu *vcpu, gva_t addr,
                 }
 
                 if (is_large_pte(*sptep)) {
-                        rmap_remove(vcpu->kvm, sptep);
-                        __set_spte(sptep, shadow_trap_nonpresent_pte);
+                        drop_spte(vcpu->kvm, sptep, shadow_trap_nonpresent_pte);
                         kvm_flush_remote_tlbs(vcpu->kvm);
                 }
 
@@ -516,12 +515,13 @@ static void FNAME(invlpg)(struct kvm_vcpu *vcpu, gva_t gva)
                         pte_gpa += (sptep - sp->spt) * sizeof(pt_element_t);
 
                         if (is_shadow_present_pte(*sptep)) {
-                                rmap_remove(vcpu->kvm, sptep);
                                 if (is_large_pte(*sptep))
                                         --vcpu->kvm->stat.lpages;
+                                drop_spte(vcpu->kvm, sptep,
+                                          shadow_trap_nonpresent_pte);
                                 need_flush = 1;
-                        }
-                        __set_spte(sptep, shadow_trap_nonpresent_pte);
+                        } else
+                                __set_spte(sptep, shadow_trap_nonpresent_pte);
                         break;
                 }
 
@@ -637,12 +637,11 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
                       !is_present_gpte(gpte) || !(gpte & PT_ACCESSED_MASK)) {
                         u64 nonpresent;
 
-                        rmap_remove(vcpu->kvm, &sp->spt[i]);
                         if (is_present_gpte(gpte) || !clear_unsync)
                                 nonpresent = shadow_trap_nonpresent_pte;
                         else
                                 nonpresent = shadow_notrap_nonpresent_pte;
-                        __set_spte(&sp->spt[i], nonpresent);
+                        drop_spte(vcpu->kvm, &sp->spt[i], nonpresent);
                         continue;
                 }