KVM: x86: avoid loading PDPTRs after migration when possible

if new KVM_*_SREGS2 ioctls are used, the PDPTRs are
a part of the migration state and are correctly
restored by those ioctls.
Signed-off-by: NMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210607090203.133058-9-mlevitsk@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -862,6 +862,12 @@ struct kvm_vcpu_arch {
 	/* Protected Guests */
 	bool guest_state_protected;
 
+	/*
+	 * Set when PDPTS were loaded directly by the userspace without
+	 * reading the guest memory
+	 */
+	bool pdptrs_from_userspace;
+
 #if IS_ENABLED(CONFIG_HYPERV)
 	hpa_t hv_root_tdp;
 #endif

arch/x86/kvm/svm/nested.c

@@ -1367,7 +1367,8 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 	if (WARN_ON(!is_guest_mode(vcpu)))
 		return true;
 
-	if (!nested_npt_enabled(svm) && is_pae_paging(vcpu))
+	if (!vcpu->arch.pdptrs_from_userspace &&
+	    !nested_npt_enabled(svm) && is_pae_paging(vcpu))
 		/*
 		 * Reload the guest's PDPTRs since after a migration
 		 * the guest CR3 might be restored prior to setting the nested

arch/x86/kvm/vmx/nested.c

@@ -3122,7 +3122,8 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 	struct page *page;
 	u64 hpa;
 
-	if (!nested_cpu_has_ept(vmcs12) && is_pae_paging(vcpu)) {
+	if (!vcpu->arch.pdptrs_from_userspace &&
+	    !nested_cpu_has_ept(vmcs12) && is_pae_paging(vcpu)) {
 		/*
 		 * Reload the guest's PDPTRs since after a migration
 		 * the guest CR3 might be restored prior to setting the nested

arch/x86/kvm/x86.c

@@ -820,6 +820,8 @@ 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);
+	vcpu->arch.pdptrs_from_userspace = false;
+
 out:
 
 	return ret;
@@ -10265,6 +10267,7 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
 
 		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
 		mmu_reset_needed = 1;
+		vcpu->arch.pdptrs_from_userspace = true;
 	}
 	if (mmu_reset_needed)
 		kvm_mmu_reset_context(vcpu);