Commit 63d28a25 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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: default avatarRobert Hoo <robert.hu@linux.intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c4b33d28

arch/x86/kvm/mmu/tdp_mmu.c

+19 −21
Original line number Diff line number Diff line
@@ -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;

}