KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET_SREGS2

This is a new version of KVM_GET_SREGS / KVM_SET_SREGS.

It has the following changes:
* Has flags for future extensions
* Has vcpu's PDPTRs, allowing to save/restore them on migration.
* Lacks obsolete interrupt bitmap (done now via KVM_SET_VCPU_EVENTS)

New capability, KVM_CAP_SREGS2 is added to signal
the userspace of this ioctl.

Signed-off-by: Maxim Levitsky <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

Documentation/virt/kvm/api.rst

···
 The KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST type may not be used
 with the KVM_XEN_VCPU_GET_ATTR ioctl.
 
+
+4.131 KVM_GET_SREGS2
+------------------
+
+:Capability: KVM_CAP_SREGS2
+:Architectures: x86
+:Type: vcpu ioctl
+:Parameters: struct kvm_sregs2 (out)
+:Returns: 0 on success, -1 on error
+
+Reads special registers from the vcpu.
+This ioctl (when supported) replaces the KVM_GET_SREGS.
+
+::
+
+struct kvm_sregs2 {
+	/* out (KVM_GET_SREGS2) / in (KVM_SET_SREGS2) */
+	struct kvm_segment cs, ds, es, fs, gs, ss;
+	struct kvm_segment tr, ldt;
+	struct kvm_dtable gdt, idt;
+	__u64 cr0, cr2, cr3, cr4, cr8;
+	__u64 efer;
+	__u64 apic_base;
+	__u64 flags;
+	__u64 pdptrs[4];
+};
+
+flags values for ``kvm_sregs2``:
+
+``KVM_SREGS2_FLAGS_PDPTRS_VALID``
+
+  Indicates thats the struct contain valid PDPTR values.
+
+
+4.132 KVM_SET_SREGS2
+------------------
+
+:Capability: KVM_CAP_SREGS2
+:Architectures: x86
+:Type: vcpu ioctl
+:Parameters: struct kvm_sregs2 (in)
+:Returns: 0 on success, -1 on error
+
+Writes special registers into the vcpu.
+See KVM_GET_SREGS2 for the data structures.
+This ioctl (when supported) replaces the KVM_SET_SREGS.
+
+
 5. The kvm_run structure
 ========================
 

arch/x86/include/uapi/asm/kvm.h

···
 	__u64 interrupt_bitmap[(KVM_NR_INTERRUPTS + 63) / 64];
 };
 
+struct kvm_sregs2 {
+	/* out (KVM_GET_SREGS2) / in (KVM_SET_SREGS2) */
+	struct kvm_segment cs, ds, es, fs, gs, ss;
+	struct kvm_segment tr, ldt;
+	struct kvm_dtable gdt, idt;
+	__u64 cr0, cr2, cr3, cr4, cr8;
+	__u64 efer;
+	__u64 apic_base;
+	__u64 flags;
+	__u64 pdptrs[4];
+};
+#define KVM_SREGS2_FLAGS_PDPTRS_VALID 1
+
 /* for KVM_GET_FPU and KVM_SET_FPU */
 struct kvm_fpu {
 	__u8  fpr[8][16];

arch/x86/kvm/kvm_cache_regs.h

···
 	return vcpu->arch.walk_mmu->pdptrs[index];
 }
 
+static inline void kvm_pdptr_write(struct kvm_vcpu *vcpu, int index, u64 value)
+{
+	vcpu->arch.walk_mmu->pdptrs[index] = value;
+}
+
 static inline ulong kvm_read_cr0_bits(struct kvm_vcpu *vcpu, ulong mask)
 {
 	ulong tmask = mask & KVM_POSSIBLE_CR0_GUEST_BITS;

arch/x86/kvm/x86.c

···
 static void store_regs(struct kvm_vcpu *vcpu);
 static int sync_regs(struct kvm_vcpu *vcpu);
 
+static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
+static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
+
 struct kvm_x86_ops kvm_x86_ops __read_mostly;
 EXPORT_SYMBOL_GPL(kvm_x86_ops);
 
···
 
 	memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
 	kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
-
 out:
 
 	return ret;
···
 	case KVM_CAP_SGX_ATTRIBUTE:
 #endif
 	case KVM_CAP_VM_COPY_ENC_CONTEXT_FROM:
+	case KVM_CAP_SREGS2:
 		r = 1;
 		break;
 	case KVM_CAP_SET_GUEST_DEBUG2:
···
 	void __user *argp = (void __user *)arg;
 	int r;
 	union {
+		struct kvm_sregs2 *sregs2;
 		struct kvm_lapic_state *lapic;
 		struct kvm_xsave *xsave;
 		struct kvm_xcrs *xcrs;
···
 		break;
 	}
 #endif
+	case KVM_GET_SREGS2: {
+		u.sregs2 = kzalloc(sizeof(struct kvm_sregs2), GFP_KERNEL);
+		r = -ENOMEM;
+		if (!u.sregs2)
+			goto out;
+		__get_sregs2(vcpu, u.sregs2);
+		r = -EFAULT;
+		if (copy_to_user(argp, u.sregs2, sizeof(struct kvm_sregs2)))
+			goto out;
+		r = 0;
+		break;
+	}
+	case KVM_SET_SREGS2: {
+		u.sregs2 = memdup_user(argp, sizeof(struct kvm_sregs2));
+		if (IS_ERR(u.sregs2)) {
+			r = PTR_ERR(u.sregs2);
+			u.sregs2 = NULL;
+			goto out;
+		}
+		r = __set_sregs2(vcpu, u.sregs2);
+		break;
+	}
 	default:
 		r = -EINVAL;
 	}
···
 }
 EXPORT_SYMBOL_GPL(kvm_get_cs_db_l_bits);
 
-static void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+static void __get_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 {
 	struct desc_ptr dt;
 
···
 	sregs->cr8 = kvm_get_cr8(vcpu);
 	sregs->efer = vcpu->arch.efer;
 	sregs->apic_base = kvm_get_apic_base(vcpu);
+}
 
-	memset(sregs->interrupt_bitmap, 0, sizeof(sregs->interrupt_bitmap));
+static void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+{
+	__get_sregs_common(vcpu, sregs);
+
+	if (vcpu->arch.guest_state_protected)
+		return;
 
 	if (vcpu->arch.interrupt.injected && !vcpu->arch.interrupt.soft)
 		set_bit(vcpu->arch.interrupt.nr,
 			(unsigned long *)sregs->interrupt_bitmap);
+}
+
+static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
+{
+	int i;
+
+	__get_sregs_common(vcpu, (struct kvm_sregs *)sregs2);
+
+	if (vcpu->arch.guest_state_protected)
+		return;
+
+	if (is_pae_paging(vcpu)) {
+		for (i = 0 ; i < 4 ; i++)
+			sregs2->pdptrs[i] = kvm_pdptr_read(vcpu, i);
+		sregs2->flags |= KVM_SREGS2_FLAGS_PDPTRS_VALID;
+	}
 }
 
 int kvm_arch_vcpu_ioctl_get_sregs(struct kvm_vcpu *vcpu,
···
 	return kvm_is_valid_cr4(vcpu, sregs->cr4);
 }
 
-static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+static int __set_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs,
+		int *mmu_reset_needed, bool update_pdptrs)
 {
 	struct msr_data apic_base_msr;
-	int mmu_reset_needed = 0;
-	int pending_vec, max_bits, idx;
+	int idx;
 	struct desc_ptr dt;
-	int ret = -EINVAL;
 
 	if (!kvm_is_valid_sregs(vcpu, sregs))
-		goto out;
+		return -EINVAL;
 
 	apic_base_msr.data = sregs->apic_base;
 	apic_base_msr.host_initiated = true;
 	if (kvm_set_apic_base(vcpu, &apic_base_msr))
-		goto out;
+		return -EINVAL;
 
 	if (vcpu->arch.guest_state_protected)
-		goto skip_protected_regs;
+		return 0;
 
 	dt.size = sregs->idt.limit;
 	dt.address = sregs->idt.base;
···
 	static_call(kvm_x86_set_gdt)(vcpu, &dt);
 
 	vcpu->arch.cr2 = sregs->cr2;
-	mmu_reset_needed |= kvm_read_cr3(vcpu) != sregs->cr3;
+	*mmu_reset_needed |= kvm_read_cr3(vcpu) != sregs->cr3;
 	vcpu->arch.cr3 = sregs->cr3;
 	kvm_register_mark_available(vcpu, VCPU_EXREG_CR3);
 
 	kvm_set_cr8(vcpu, sregs->cr8);
 
-	mmu_reset_needed |= vcpu->arch.efer != sregs->efer;
+	*mmu_reset_needed |= vcpu->arch.efer != sregs->efer;
 	static_call(kvm_x86_set_efer)(vcpu, sregs->efer);
 
-	mmu_reset_needed |= kvm_read_cr0(vcpu) != sregs->cr0;
+	*mmu_reset_needed |= kvm_read_cr0(vcpu) != sregs->cr0;
 	static_call(kvm_x86_set_cr0)(vcpu, sregs->cr0);
 	vcpu->arch.cr0 = sregs->cr0;
 
-	mmu_reset_needed |= kvm_read_cr4(vcpu) != sregs->cr4;
+	*mmu_reset_needed |= kvm_read_cr4(vcpu) != sregs->cr4;
 	static_call(kvm_x86_set_cr4)(vcpu, sregs->cr4);
 
-	idx = srcu_read_lock(&vcpu->kvm->srcu);
-	if (is_pae_paging(vcpu)) {
-		load_pdptrs(vcpu, vcpu->arch.walk_mmu, kvm_read_cr3(vcpu));
-		mmu_reset_needed = 1;
+	if (update_pdptrs) {
+		idx = srcu_read_lock(&vcpu->kvm->srcu);
+		if (is_pae_paging(vcpu)) {
+			load_pdptrs(vcpu, vcpu->arch.walk_mmu, kvm_read_cr3(vcpu));
+			*mmu_reset_needed = 1;
+		}
+		srcu_read_unlock(&vcpu->kvm->srcu, idx);
 	}
-	srcu_read_unlock(&vcpu->kvm->srcu, idx);
-
-	if (mmu_reset_needed)
-		kvm_mmu_reset_context(vcpu);
 
 	kvm_set_segment(vcpu, &sregs->cs, VCPU_SREG_CS);
 	kvm_set_segment(vcpu, &sregs->ds, VCPU_SREG_DS);
···
 	    !is_protmode(vcpu))
 		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
 
-skip_protected_regs:
+	return 0;
+}
+
+static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+{
+	int pending_vec, max_bits;
+	int mmu_reset_needed = 0;
+	int ret = __set_sregs_common(vcpu, sregs, &mmu_reset_needed, true);
+
+	if (ret)
+		return ret;
+
+	if (mmu_reset_needed)
+		kvm_mmu_reset_context(vcpu);
+
 	max_bits = KVM_NR_INTERRUPTS;
 	pending_vec = find_first_bit(
 		(const unsigned long *)sregs->interrupt_bitmap, max_bits);
+
 	if (pending_vec < max_bits) {
 		kvm_queue_interrupt(vcpu, pending_vec, false);
 		pr_debug("Set back pending irq %d\n", pending_vec);
+		kvm_make_request(KVM_REQ_EVENT, vcpu);
 	}
+	return 0;
+}
 
-	kvm_make_request(KVM_REQ_EVENT, vcpu);
+static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
+{
+	int mmu_reset_needed = 0;
+	bool valid_pdptrs = sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID;
+	bool pae = (sregs2->cr0 & X86_CR0_PG) && (sregs2->cr4 & X86_CR4_PAE) &&
+		!(sregs2->efer & EFER_LMA);
+	int i, ret;
 
-	ret = 0;
-out:
-	return ret;
+	if (sregs2->flags & ~KVM_SREGS2_FLAGS_PDPTRS_VALID)
+		return -EINVAL;
+
+	if (valid_pdptrs && (!pae || vcpu->arch.guest_state_protected))
+		return -EINVAL;
+
+	ret = __set_sregs_common(vcpu, (struct kvm_sregs *)sregs2,
+				 &mmu_reset_needed, !valid_pdptrs);
+	if (ret)
+		return ret;
+
+	if (valid_pdptrs) {
+		for (i = 0; i < 4 ; i++)
+			kvm_pdptr_write(vcpu, i, sregs2->pdptrs[i]);
+
+		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
+		mmu_reset_needed = 1;
+	}
+	if (mmu_reset_needed)
+		kvm_mmu_reset_context(vcpu);
+	return 0;
 }
 
 int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,

include/uapi/linux/kvm.h

···
 #define KVM_CAP_VM_COPY_ENC_CONTEXT_FROM 197
 #define KVM_CAP_PTP_KVM 198
 #define KVM_CAP_HYPERV_ENFORCE_CPUID 199
+#define KVM_CAP_SREGS2 200
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
···
 /* Per-vCPU Xen attributes */
 #define KVM_XEN_VCPU_GET_ATTR	_IOWR(KVMIO, 0xca, struct kvm_xen_vcpu_attr)
 #define KVM_XEN_VCPU_SET_ATTR	_IOW(KVMIO,  0xcb, struct kvm_xen_vcpu_attr)
+
+#define KVM_GET_SREGS2             _IOR(KVMIO,  0xcc, struct kvm_sregs2)
+#define KVM_SET_SREGS2             _IOW(KVMIO,  0xcd, struct kvm_sregs2)
 
 struct kvm_xen_vcpu_attr {
 	__u16 type;