[PATCH 3/6] Add dirty quota migration capability and handle vCPU page fault for dirty quota context.

[Shivam Kumar <shivam.kumar1@nutanix.com>]

When a dirty quota migration is initiated from QEMU side, the following
things happen:

1. An mmap ioctl is called for each vCPU to mmap the dirty quota context.
This results into vCPU page fault which needs to be handled.
2. An ioctl to start dirty quota migration is called from QEMU and must be
handled. This happens once QEMU is ready to start the migration.

Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
Signed-off-by: Shaju Abraham <shaju.abraham@nutanix.com>
Signed-off-by: Manish Mishra <manish.mishra@nutanix.com>
---
 include/linux/dirty_quota_migration.h |  6 ++++++
 include/uapi/linux/kvm.h              |  1 +
 virt/kvm/dirty_quota_migration.c      |  6 ++++++
 virt/kvm/kvm_main.c                   | 15 +++++++++++++++
 4 files changed, 28 insertions(+)

diff --git a/include/linux/dirty_quota_migration.h b/include/linux/dirty_quota_migration.h
index 2d6e5cd17be6..a9a54c38ee54 100644
--- a/include/linux/dirty_quota_migration.h
+++ b/include/linux/dirty_quota_migration.h
@@ -3,11 +3,17 @@
 #define DIRTY_QUOTA_MIGRATION_H
 #include <linux/kvm.h>
 
+#ifndef KVM_DIRTY_QUOTA_PAGE_OFFSET
+#define KVM_DIRTY_QUOTA_PAGE_OFFSET 64
+#endif
+
 struct vCPUDirtyQuotaContext {
 	u64 dirty_counter;
 	u64 dirty_quota;
 };
 
 int kvm_vcpu_dirty_quota_alloc(struct vCPUDirtyQuotaContext **vCPUdqctx);
+struct page *kvm_dirty_quota_context_get_page(
+		struct vCPUDirtyQuotaContext *vCPUdqctx, u32 offset);
 
 #endif  /* DIRTY_QUOTA_MIGRATION_H */
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index a067410ebea5..3649a3bb9bb8 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1112,6 +1112,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_BINARY_STATS_FD 203
 #define KVM_CAP_EXIT_ON_EMULATION_FAILURE 204
 #define KVM_CAP_ARM_MTE 205
+#define KVM_CAP_DIRTY_QUOTA_MIGRATION 206
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
diff --git a/virt/kvm/dirty_quota_migration.c b/virt/kvm/dirty_quota_migration.c
index 262f071aac0c..7e9ace760939 100644
--- a/virt/kvm/dirty_quota_migration.c
+++ b/virt/kvm/dirty_quota_migration.c
@@ -12,3 +12,9 @@ int kvm_vcpu_dirty_quota_alloc(struct vCPUDirtyQuotaContext **vCPUdqctx)
 	memset((*vCPUdqctx), 0, size);
 	return 0;
 }
+
+struct page *kvm_dirty_quota_context_get_page(
+		struct vCPUDirtyQuotaContext *vCPUdqctx, u32 offset)
+{
+	return vmalloc_to_page((void *)vCPUdqctx + offset * PAGE_SIZE);
+}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f232a16a26e7..95f857c50bf2 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3511,6 +3511,9 @@ static vm_fault_t kvm_vcpu_fault(struct vm_fault *vmf)
 		page = kvm_dirty_ring_get_page(
 		    &vcpu->dirty_ring,
 		    vmf->pgoff - KVM_DIRTY_LOG_PAGE_OFFSET);
+	else if (vmf->pgoff == KVM_DIRTY_QUOTA_PAGE_OFFSET)
+		page = kvm_dirty_quota_context_get_page(vcpu->vCPUdqctx,
+				vmf->pgoff - KVM_DIRTY_QUOTA_PAGE_OFFSET);
 	else
 		return kvm_arch_vcpu_fault(vcpu, vmf);
 	get_page(page);
@@ -4263,6 +4266,15 @@ static int kvm_vm_ioctl_reset_dirty_pages(struct kvm *kvm)
 	return cleared;
 }
 
+static int kvm_vm_ioctl_enable_dirty_quota_migration(struct kvm *kvm,
+		bool dirty_quota_migration_enabled)
+{
+	mutex_lock(&kvm->lock);
+	kvm->dirty_quota_migration_enabled = dirty_quota_migration_enabled;
+	mutex_unlock(&kvm->lock);
+	return 0;
+}
+
 int __attribute__((weak)) kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 						  struct kvm_enable_cap *cap)
 {
@@ -4295,6 +4307,9 @@ static int kvm_vm_ioctl_enable_cap_generic(struct kvm *kvm,
 	}
 	case KVM_CAP_DIRTY_LOG_RING:
 		return kvm_vm_ioctl_enable_dirty_log_ring(kvm, cap->args[0]);
+	case KVM_CAP_DIRTY_QUOTA_MIGRATION:
+		return kvm_vm_ioctl_enable_dirty_quota_migration(kvm,
+				cap->args[0]);
 	default:
 		return kvm_vm_ioctl_enable_cap(kvm, cap);
 	}
-- 
2.22.3