[v3,07/11] KVM: guest_memfd: Add a guest_memfd() flag to initialize it as mappable

Commit Message

Fuad Tabba Oct. 10, 2024, 8:59 a.m. UTC

Not all use cases require guest_memfd() to be mappable by the
host when first created. Add a new flag,
GUEST_MEMFD_FLAG_INIT_MAPPABLE, which when set on
KVM_CREATE_GUEST_MEMFD initializes the memory as mappable by the
host. Otherwise, memory is private until shared by the guest with
the host.

Signed-off-by: Fuad Tabba <[e-mail]>
---
 Documentation/virt/kvm/api.rst | 4 ++++
 include/uapi/linux/kvm.h       | 1 +
 virt/kvm/guest_memfd.c         | 6 +++++-
 3 files changed, 10 insertions(+), 1 deletion(-)

Patch

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index e32471977d0a..c503f9443335 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6380,6 +6380,10 @@  most one mapping per page, i.e. binding multiple memory regions to a single
 guest_memfd range is not allowed (any number of memory regions can be bound to
 a single guest_memfd file, but the bound ranges must not overlap).
 
+If the capability KVM_CAP_GUEST_MEMFD_MAPPABLE is supported, then the flags
+field supports GUEST_MEMFD_FLAG_INIT_MAPPABLE, which initializes the memory
+as mappable by the host.
+
 See KVM_SET_USER_MEMORY_REGION2 for additional details.
 
 4.143 KVM_PRE_FAULT_MEMORY
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 2c6057bab71c..751f167d0f33 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1558,6 +1558,7 @@  struct kvm_memory_attributes {
 #define KVM_MEMORY_ATTRIBUTE_PRIVATE           (1ULL << 3)
 
 #define KVM_CREATE_GUEST_MEMFD	_IOWR(KVMIO,  0xd4, struct kvm_create_guest_memfd)
+#define GUEST_MEMFD_FLAG_INIT_MAPPABLE		BIT(0)
 
 struct kvm_create_guest_memfd {
 	__u64 size;
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index df3a6f05a16e..9080fa29cd8c 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -734,7 +734,8 @@  static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 		goto err_gmem;
 	}
 
-	if (IS_ENABLED(CONFIG_KVM_GMEM_MAPPABLE)) {
+	if (IS_ENABLED(CONFIG_KVM_GMEM_MAPPABLE) &&
+	    (flags & GUEST_MEMFD_FLAG_INIT_MAPPABLE)) {
 		err = gmem_set_mappable(file_inode(file), 0, size >> PAGE_SHIFT);
 		if (err) {
 			fput(file);
@@ -763,6 +764,9 @@  int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args)
 	u64 flags = args->flags;
 	u64 valid_flags = 0;
 
+	if (IS_ENABLED(CONFIG_KVM_GMEM_MAPPABLE))
+		valid_flags |= GUEST_MEMFD_FLAG_INIT_MAPPABLE;
+
 	if (flags & ~valid_flags)
 		return -EINVAL;