KVM: X86: Update mmu->pdptrs only when it is changed

It is unchanged in most cases.
Signed-off-by: NLai Jiangshan <laijs@linux.alibaba.com>
Message-Id: <20211111144527.88852-1-jiangshanlai@gmail.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -828,9 +828,12 @@ int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3)
 		}
 	}
 
-	memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
-	kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
-	kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
+	kvm_register_mark_available(vcpu, VCPU_EXREG_PDPTR);
+	if (memcmp(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs))) {
+		memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
+		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
+		kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
+	}
 	vcpu->arch.pdptrs_from_userspace = false;
 
 	return 1;