[PATCH kvmtool v2 3/4] Add support for registering guest_memfd-backed memory regions

[Fuad Tabba <fuad.tabba@linux.dev>]

Extend kvm__register_mem() with a guest_memfd file descriptor and
offset. A bank with a guest_memfd is registered with
KVM_SET_USER_MEMORY_REGION2 and KVM_MEM_GUEST_MEMFD, binding the
memslot to the file. This prepares for backing guest RAM with
guest_memfd on arm64.

Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 hw/cfi_flash.c    |  2 +-
 include/kvm/kvm.h | 15 +++++++++++++--
 kvm.c             | 36 ++++++++++++++++++++++++++----------
 3 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/hw/cfi_flash.c b/hw/cfi_flash.c
index b68d9e0..4413955 100644
--- a/hw/cfi_flash.c
+++ b/hw/cfi_flash.c
@@ -451,7 +451,7 @@ static int map_flash_memory(struct kvm *kvm, struct cfi_flash_device *sfdev)
 	int ret;
 
 	ret = kvm__register_mem(kvm, sfdev->base_addr, sfdev->size,
-				sfdev->flash_memory,
+				sfdev->flash_memory, -1, 0,
 				KVM_MEM_TYPE_RAM | KVM_MEM_TYPE_READONLY);
 	if (!ret)
 		sfdev->is_mapped = true;
diff --git a/include/kvm/kvm.h b/include/kvm/kvm.h
index eb23e2f..5e7b5eb 100644
--- a/include/kvm/kvm.h
+++ b/include/kvm/kvm.h
@@ -128,11 +128,22 @@ bool kvm__emulate_io(struct kvm_cpu *vcpu, u16 port, void *data, int direction,
 bool kvm__emulate_mmio(struct kvm_cpu *vcpu, u64 phys_addr, u8 *data, u32 len, u8 is_write);
 int kvm__destroy_mem(struct kvm *kvm, u64 guest_phys, u64 size, void *userspace_addr);
 int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size, void *userspace_addr,
+		      int guest_memfd, u64 guest_memfd_offset,
 		      enum kvm_mem_type type);
 static inline int kvm__register_ram(struct kvm *kvm, u64 guest_phys, u64 size,
 				    void *userspace_addr)
 {
 	return kvm__register_mem(kvm, guest_phys, size, userspace_addr,
+				 -1, 0, KVM_MEM_TYPE_RAM);
+}
+
+static inline int kvm__register_ram_guest_memfd(struct kvm *kvm, u64 guest_phys,
+						u64 size, void *userspace_addr,
+						int guest_memfd,
+						u64 guest_memfd_offset)
+{
+	return kvm__register_mem(kvm, guest_phys, size, userspace_addr,
+				 guest_memfd, guest_memfd_offset,
 				 KVM_MEM_TYPE_RAM);
 }
 
@@ -140,13 +151,13 @@ static inline int kvm__register_dev_mem(struct kvm *kvm, u64 guest_phys,
 					u64 size, void *userspace_addr)
 {
 	return kvm__register_mem(kvm, guest_phys, size, userspace_addr,
-				 KVM_MEM_TYPE_DEVICE);
+				 -1, 0, KVM_MEM_TYPE_DEVICE);
 }
 
 static inline int kvm__reserve_mem(struct kvm *kvm, u64 guest_phys, u64 size)
 {
 	return kvm__register_mem(kvm, guest_phys, size, NULL,
-				 KVM_MEM_TYPE_RESERVED);
+				 -1, 0, KVM_MEM_TYPE_RESERVED);
 }
 
 int __must_check kvm__register_iotrap(struct kvm *kvm, u64 phys_addr, u64 len,
diff --git a/kvm.c b/kvm.c
index 95ccfcb..947721b 100644
--- a/kvm.c
+++ b/kvm.c
@@ -237,9 +237,9 @@ out:
 }
 
 int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size,
-		      void *userspace_addr, enum kvm_mem_type type)
+		      void *userspace_addr, int guest_memfd,
+		      u64 guest_memfd_offset, enum kvm_mem_type type)
 {
-	struct kvm_userspace_memory_region mem;
 	struct kvm_mem_bank *merged = NULL;
 	struct kvm_mem_bank *bank;
 	struct list_head *prev_entry;
@@ -320,15 +320,31 @@ int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size,
 		flags |= KVM_MEM_READONLY;
 
 	if (type != KVM_MEM_TYPE_RESERVED) {
-		mem = (struct kvm_userspace_memory_region) {
-			.slot			= slot,
-			.flags			= flags,
-			.guest_phys_addr	= guest_phys,
-			.memory_size		= size,
-			.userspace_addr		= (unsigned long)userspace_addr,
-		};
+		if (guest_memfd >= 0) {
+			struct kvm_userspace_memory_region2 mem2 = {
+				.slot			= slot,
+				.flags			= flags | KVM_MEM_GUEST_MEMFD,
+				.guest_phys_addr	= guest_phys,
+				.memory_size		= size,
+				.userspace_addr		= (unsigned long)userspace_addr,
+				.guest_memfd		= guest_memfd,
+				.guest_memfd_offset	= guest_memfd_offset,
+			};
 
-		ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION, &mem);
+			ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION2,
+				    &mem2);
+		} else {
+			struct kvm_userspace_memory_region mem = {
+				.slot			= slot,
+				.flags			= flags,
+				.guest_phys_addr	= guest_phys,
+				.memory_size		= size,
+				.userspace_addr		= (unsigned long)userspace_addr,
+			};
+
+			ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION,
+				    &mem);
+		}
 		if (ret < 0) {
 			ret = -errno;
 			goto out;
-- 
2.39.5