Register private memslot to fd-based memory backing store and handle the
memfile notifiers to zap the existing mappings.

Currently the register is happened at memslot creating time and the
initial support does not include page migration/swap.

KVM_MEM_PRIVATE is not exposed by default, architecture code can turn
on it by implementing kvm_arch_private_mem_supported().

A 'kvm' reference is added in memslot structure since in
memfile_notifier callbacks we can only obtain a memslot reference while
kvm is need to do the zapping. The zapping itself reuses code from
existing mmu notifier handling.

Co-developed-by: Yu Zhang <redacted>
Signed-off-by: Yu Zhang <redacted>
Signed-off-by: Chao Peng <redacted>
---
 include/linux/kvm_host.h |  10 ++-
 virt/kvm/kvm_main.c      | 132 ++++++++++++++++++++++++++++++++++++---
 2 files changed, 131 insertions(+), 11 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b0a7910505ed..00efb4b96bc7 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h

@@ -246,7 +246,7 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
 #endif
 
-#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
+#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_MEMFILE_NOTIFIER)
 struct kvm_gfn_range {
 	struct kvm_memory_slot *slot;
 	gfn_t start;

@@ -577,6 +577,7 @@ struct kvm_memory_slot {
 	struct file *private_file;
 	loff_t private_offset;
 	struct memfile_notifier notifier;
+	struct kvm *kvm;
 };
 
 static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)

@@ -769,9 +770,13 @@ struct kvm {
 	struct hlist_head irq_ack_notifier_list;
 #endif
 
+#if (defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)) ||\
+	defined(CONFIG_MEMFILE_NOTIFIER)
+	unsigned long mmu_notifier_seq;
+#endif
+
 #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
 	struct mmu_notifier mmu_notifier;
-	unsigned long mmu_notifier_seq;
 	long mmu_notifier_count;
 	unsigned long mmu_notifier_range_start;
 	unsigned long mmu_notifier_range_end;

@@ -1438,6 +1443,7 @@ bool kvm_arch_dy_has_pending_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_post_init_vm(struct kvm *kvm);
 void kvm_arch_pre_destroy_vm(struct kvm *kvm);
 int kvm_arch_create_vm_debugfs(struct kvm *kvm);
+bool kvm_arch_private_mem_supported(struct kvm *kvm);
 
 #ifndef __KVM_HAVE_ARCH_VM_ALLOC
 /*

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index db9d39a2d3a6..f93ac7cdfb53 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c

@@ -843,6 +843,73 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
 
 #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
 
+#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM
+static void kvm_private_mem_notifier_handler(struct memfile_notifier *notifier,
+					     pgoff_t start, pgoff_t end)
+{
+	int idx;
+	struct kvm_memory_slot *slot = container_of(notifier,
+						    struct kvm_memory_slot,
+						    notifier);
+	struct kvm_gfn_range gfn_range = {
+		.slot		= slot,
+		.start		= start - (slot->private_offset >> PAGE_SHIFT),
+		.end		= end - (slot->private_offset >> PAGE_SHIFT),