KVM: x86/mmu: simplify kvm_tdp_mmu_map flow when guest has to retry

A removed SPTE is never present, hence the "if" in kvm_tdp_mmu_map
only fails in the exact same conditions that the earlier loop
tested in order to issue a  "break". So, instead of checking twice the
condition (upper level SPTEs could not be created or was frozen), just
exit the loop with a goto---the usual poor-man C replacement for RAII
early returns.

While at it, do not use the "ret" variable for return values of
functions that do not return a RET_PF_* enum.  This is clearer
and also makes it possible to initialize ret to RET_PF_RETRY.

Suggested-by: Robert Hoo <robert.hu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index e085967..771210c 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1159,7 +1159,7 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
        struct kvm *kvm = vcpu->kvm;
        struct tdp_iter iter;
        struct kvm_mmu_page *sp;
-       int ret;
+       int ret = RET_PF_RETRY;
 
        kvm_mmu_hugepage_adjust(vcpu, fault);
 
@@ -1168,23 +1168,25 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
        rcu_read_lock();
 
        tdp_mmu_for_each_pte(iter, mmu, fault->gfn, fault->gfn + 1) {
+               int r;
+
                if (fault->nx_huge_page_workaround_enabled)
                        disallowed_hugepage_adjust(fault, iter.old_spte, iter.level);
 
                if (iter.level == fault->goal_level)
                        break;
 
-               /* Step down into the lower level page table if it exists. */
-               if (is_shadow_present_pte(iter.old_spte) &&
-                   !is_large_pte(iter.old_spte))
-                       continue;
-
                /*
                 * If SPTE has been frozen by another thread, just give up and
                 * retry, avoiding unnecessary page table allocation and free.
                 */
                if (is_removed_spte(iter.old_spte))
-                       break;
+                       goto retry;
+
+               /* Step down into the lower level page table if it exists. */
+               if (is_shadow_present_pte(iter.old_spte) &&
+                   !is_large_pte(iter.old_spte))
+                       continue;
 
                /*
                 * The SPTE is either non-present or points to a huge page that
@@ -1196,13 +1198,17 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
                sp->nx_huge_page_disallowed = fault->huge_page_disallowed;
 
                if (is_shadow_present_pte(iter.old_spte))
-                       ret = tdp_mmu_split_huge_page(kvm, &iter, sp, true);
+                       r = tdp_mmu_split_huge_page(kvm, &iter, sp, true);
                else
-                       ret = tdp_mmu_link_sp(kvm, &iter, sp, true);
+                       r = tdp_mmu_link_sp(kvm, &iter, sp, true);
 
-               if (ret) {
+               /*
+                * Also force the guest to retry the access if the upper level SPTEs
+                * aren't in place.
+                */
+               if (r) {
                        tdp_mmu_free_sp(sp);
-                       break;
+                       goto retry;
                }
 
                if (fault->huge_page_disallowed &&
@@ -1213,18 +1219,10 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
                }
        }
 
-       /*
-        * Force the guest to retry the access if the upper level SPTEs aren't
-        * in place, or if the target leaf SPTE is frozen by another CPU.
-        */
-       if (iter.level != fault->goal_level || is_removed_spte(iter.old_spte)) {
-               rcu_read_unlock();
-               return RET_PF_RETRY;
-       }
-
        ret = tdp_mmu_map_handle_target_level(vcpu, fault, &iter);
-       rcu_read_unlock();
 
+retry:
+       rcu_read_unlock();
        return ret;
 }