KVM: arm64: Enable ring-based dirty memory tracking

Enable ring-based dirty memory tracking on ARM64:

- Enable CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL.

- Enable CONFIG_NEED_KVM_DIRTY_RING_WITH_BITMAP.

- Set KVM_DIRTY_LOG_PAGE_OFFSET for the ring buffer's physical page
offset.

- Add ARM64 specific kvm_arch_allow_write_without_running_vcpu() to
keep the site of saving vgic/its tables out of the no-running-vcpu
radar.

Signed-off-by: Gavin Shan <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

Documentation/virt/kvm/api.rst

···
 8.29 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL
 ----------------------------------------------------------
 
-:Architectures: x86
+:Architectures: x86, arm64
 :Parameters: args[0] - size of the dirty log ring
 
 KVM is capable of tracking dirty memory using ring buffers that are

arch/arm64/include/uapi/asm/kvm.h

···
 #define __KVM_HAVE_VCPU_EVENTS
 
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
+#define KVM_DIRTY_LOG_PAGE_OFFSET 64
 
 #define KVM_REG_SIZE(id)						\
 	(1U << (((id) & KVM_REG_SIZE_MASK) >> KVM_REG_SIZE_SHIFT))

arch/arm64/kvm/Kconfig

···
 	select KVM_VFIO
 	select HAVE_KVM_EVENTFD
 	select HAVE_KVM_IRQFD
+	select HAVE_KVM_DIRTY_RING_ACQ_REL
+	select NEED_KVM_DIRTY_RING_WITH_BITMAP
 	select HAVE_KVM_MSI
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_IRQ_ROUTING

arch/arm64/kvm/arm.c

···
 
 		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
 			return kvm_vcpu_suspend(vcpu);
+
+		if (kvm_dirty_ring_check_request(vcpu))
+			return 0;
 	}
 
 	return 1;

arch/arm64/kvm/vgic/vgic-its.c

···
 static int vgic_its_ctrl(struct kvm *kvm, struct vgic_its *its, u64 attr)
 {
 	const struct vgic_its_abi *abi = vgic_its_get_abi(its);
+	struct vgic_dist *dist = &kvm->arch.vgic;
 	int ret = 0;
 
 	if (attr == KVM_DEV_ARM_VGIC_CTRL_INIT) /* Nothing to do */
···
 		vgic_its_reset(kvm, its);
 		break;
 	case KVM_DEV_ARM_ITS_SAVE_TABLES:
+		dist->save_its_tables_in_progress = true;
 		ret = abi->save_tables(its);
+		dist->save_its_tables_in_progress = false;
 		break;
 	case KVM_DEV_ARM_ITS_RESTORE_TABLES:
 		ret = abi->restore_tables(its);
···
 	mutex_unlock(&its->its_lock);
 	mutex_unlock(&kvm->lock);
 	return ret;
+}
+
+/*
+ * kvm_arch_allow_write_without_running_vcpu - allow writing guest memory
+ * without the running VCPU when dirty ring is enabled.
+ *
+ * The running VCPU is required to track dirty guest pages when dirty ring
+ * is enabled. Otherwise, the backup bitmap should be used to track the
+ * dirty guest pages. When vgic/its tables are being saved, the backup
+ * bitmap is used to track the dirty guest pages due to the missed running
+ * VCPU in the period.
+ */
+bool kvm_arch_allow_write_without_running_vcpu(struct kvm *kvm)
+{
+	struct vgic_dist *dist = &kvm->arch.vgic;
+
+	return dist->save_its_tables_in_progress;
 }
 
 static int vgic_its_set_attr(struct kvm_device *dev,

include/kvm/arm_vgic.h

···
 	struct vgic_io_device	dist_iodev;
 
 	bool			has_its;
+	bool			save_its_tables_in_progress;
 
 	/*
 	 * Contains the attributes and gpa of the LPI configuration table.