[PATCH 8/8] KVM: MMU: Move free_zapped_mmu_pages() out of the protection of mmu_lock

[Takuya Yoshikawa <yoshikawa_takuya_b1@xxxxxxxxxxxxx>]

We noticed that kvm_mmu_zap_all() could take hundreds of milliseconds
for zapping mmu pages with mmu_lock held.

Although we need to do conditional rescheduling for completely
fixing this issue, we can reduce the hold time to some extent by moving
free_zapped_mmu_pages() out of the protection.  Since invalid_list can
be very long, the effect is not negligible.

Note: this patch does not treat non-trivial cases.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@xxxxxxxxxxxxx>
---
 arch/x86/kvm/mmu.c |   20 +++++++++++++-------
 1 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index dd7b455..7976f55 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -2185,7 +2185,6 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int goal_nr_mmu_pages)
 			kvm_mmu_prepare_zap_page(kvm, page, &invalid_list, NULL);
 		}
 		kvm_mmu_commit_zap_page(kvm, &invalid_list);
-		free_zapped_mmu_pages(kvm, &invalid_list);
 
 		goal_nr_mmu_pages = kvm->arch.n_used_mmu_pages;
 	}
@@ -2193,6 +2192,8 @@ void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int goal_nr_mmu_pages)
 	kvm->arch.n_max_mmu_pages = goal_nr_mmu_pages;
 
 	spin_unlock(&kvm->mmu_lock);
+
+	free_zapped_mmu_pages(kvm, &invalid_list);
 }
 
 int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
@@ -2213,9 +2214,10 @@ int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
 		kvm_mmu_prepare_zap_page(kvm, sp, &invalid_list, &npos);
 	}
 	kvm_mmu_commit_zap_page(kvm, &invalid_list);
-	free_zapped_mmu_pages(kvm, &invalid_list);
 	spin_unlock(&kvm->mmu_lock);
 
+	free_zapped_mmu_pages(kvm, &invalid_list);
+
 	return r;
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_unprotect_page);
@@ -2934,10 +2936,11 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 			kvm_mmu_prepare_zap_page(vcpu->kvm, sp,
 						 &invalid_list, NULL);
 			kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
-			free_zapped_mmu_pages(vcpu->kvm, &invalid_list);
 		}
 		vcpu->arch.mmu.root_hpa = INVALID_PAGE;
 		spin_unlock(&vcpu->kvm->mmu_lock);
+
+		free_zapped_mmu_pages(vcpu->kvm, &invalid_list);
 		return;
 	}
 	for (i = 0; i < 4; ++i) {
@@ -2954,9 +2957,10 @@ static void mmu_free_roots(struct kvm_vcpu *vcpu)
 		vcpu->arch.mmu.pae_root[i] = INVALID_PAGE;
 	}
 	kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
-	free_zapped_mmu_pages(vcpu->kvm, &invalid_list);
 
 	spin_unlock(&vcpu->kvm->mmu_lock);
+
+	free_zapped_mmu_pages(vcpu->kvm, &invalid_list);
 	vcpu->arch.mmu.root_hpa = INVALID_PAGE;
 }
 
@@ -4054,10 +4058,11 @@ void kvm_mmu_pte_write(struct kvm_vcpu *vcpu, gpa_t gpa,
 	mmu_pte_write_flush_tlb(vcpu, zap_page, remote_flush, local_flush);
 
 	kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
-	free_zapped_mmu_pages(vcpu->kvm, &invalid_list);
 
 	kvm_mmu_audit(vcpu, AUDIT_POST_PTE_WRITE);
 	spin_unlock(&vcpu->kvm->mmu_lock);
+
+	free_zapped_mmu_pages(vcpu->kvm, &invalid_list);
 }
 
 int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu, gva_t gva)
@@ -4254,9 +4259,10 @@ restart:
 			goto restart;
 
 	kvm_mmu_commit_zap_page(kvm, &invalid_list);
-	free_zapped_mmu_pages(kvm, &invalid_list);
 
 	spin_unlock(&kvm->mmu_lock);
+
+	free_zapped_mmu_pages(kvm, &invalid_list);
 }
 
 static void kvm_mmu_remove_some_alloc_mmu_pages(struct kvm *kvm,
@@ -4308,10 +4314,10 @@ static int mmu_shrink(struct shrinker *shrink, struct shrink_control *sc)
 
 		kvm_mmu_remove_some_alloc_mmu_pages(kvm, &invalid_list);
 		kvm_mmu_commit_zap_page(kvm, &invalid_list);
-		free_zapped_mmu_pages(kvm, &invalid_list);
 
 		spin_unlock(&kvm->mmu_lock);
 		srcu_read_unlock(&kvm->srcu, idx);
+		free_zapped_mmu_pages(kvm, &invalid_list);
 
 		list_move_tail(&kvm->vm_list, &vm_list);
 		break;
-- 
1.7.5.4

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