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Commit fbb158cb authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: x86/mmu: Revert "Revert "KVM: MMU: zap pages in batch"" 



Now that the fast invalidate mechanism has been reintroduced, restore
the performance tweaks for fast invalidation that existed prior to its
removal.

Paraphrashing the original changelog:

  Zap at least 10 shadow pages before releasing mmu_lock to reduce the
  overhead associated with re-acquiring the lock.

  Note: "10" is an arbitrary number, speculated to be high enough so
  that a vCPU isn't stuck zapping obsolete pages for an extended period,
  but small enough so that other vCPUs aren't starved waiting for
  mmu_lock.

This reverts commit 43d2b14b.

Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 14a3c4f4

arch/x86/kvm/mmu.c

+9 −26
Original line number Diff line number Diff line
@@ -5671,12 +5671,12 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu) 
	return ret;

}





#define BATCH_ZAP_PAGES	10

static void kvm_zap_obsolete_pages(struct kvm *kvm)

{

	struct kvm_mmu_page *sp, *node;

	LIST_HEAD(invalid_list);

	int ign;

	int nr_zapped, batch = 0;



restart:

	list_for_each_entry_safe_reverse(sp, node,
@@ -5689,28 +5689,6 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) 
			break;



		/*

		 * Do not repeatedly zap a root page to avoid unnecessary

		 * KVM_REQ_MMU_RELOAD, otherwise we may not be able to

		 * progress:

		 *    vcpu 0                        vcpu 1

		 *                         call vcpu_enter_guest():

		 *                            1): handle KVM_REQ_MMU_RELOAD

		 *                                and require mmu-lock to

		 *                                load mmu

		 * repeat:

		 *    1): zap root page and

		 *        send KVM_REQ_MMU_RELOAD

		 *

		 *    2): if (cond_resched_lock(mmu-lock))

		 *

		 *                            2): hold mmu-lock and load mmu

		 *

		 *                            3): see KVM_REQ_MMU_RELOAD bit

		 *                                on vcpu->requests is set

		 *                                then return 1 to call

		 *                                vcpu_enter_guest() again.

		 *            goto repeat;

		 *

		 * Since we are reversely walking the list and the invalid

		 * list will be moved to the head, skip the invalid page

		 * can help us to avoid the infinity list walking.
@@ -5718,15 +5696,20 @@ static void kvm_zap_obsolete_pages(struct kvm *kvm) 
		if (sp->role.invalid)

			continue;



		if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {

		if (batch >= BATCH_ZAP_PAGES &&

		    (need_resched() || spin_needbreak(&kvm->mmu_lock))) {

			batch = 0;

			kvm_mmu_commit_zap_page(kvm, &invalid_list);

			cond_resched_lock(&kvm->mmu_lock);

			goto restart;

		}



		if (__kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list, &ign))

		if (__kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list,

					       &nr_zapped)) {

			batch += nr_zapped;

			goto restart;

		}

	}



	kvm_mmu_commit_zap_page(kvm, &invalid_list);

}