On 6/19/2026 8:31 AM, Ackerley Tng via B4 Relay wrote:

From: Ackerley Tng <redacted>

Introduce KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES to advertise the
availability of the KVM_SET_MEMORY_ATTRIBUTES2 ioctl.

KVM_SET_MEMORY_ATTRIBUTES2 is a guest_memfd-scoped version of the existing
KVM_SET_MEMORY_ATTRIBUTES VM ioctl. It allows userspace to manage memory
attributes, such as KVM_MEMORY_ATTRIBUTE_PRIVATE, directly on a guest_memfd
file descriptor.

This new version uses struct kvm_memory_attributes2, which adds an
error_offset field to the output. This allows KVM to return the specific
offset that triggered an error, which is especially useful for handling
EAGAIN results caused by transient page reference counts during attribute
conversions.

Update the KVM API documentation to define the new ioctl and its behavior,
and add the necessary UAPI definitions and capability checks.

Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Michael Roth <redacted>
Signed-off-by: Ackerley Tng <redacted>

Reviewed-by: Binbin Wu <redacted>

Two nits below.

 
+4.145 KVM_SET_MEMORY_ATTRIBUTES2
+---------------------------------
+
+:Capability: KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES
+:Architectures: all
+:Type: guest_memfd ioctl
+:Parameters: struct kvm_memory_attributes2 (in/out)
+:Returns: 0 on success, <0 on error
+
+Errors:
+
+  ========== ===============================================================
+  EINVAL     The specified `offset` or `size` were invalid (e.g. not

                                                   ^
                                                 was
 > +             page aligned, causes an overflow, or size is zero).

+  EFAULT     The parameter address was invalid.
+  EAGAIN     Some page within requested range had unexpected refcounts. The
+             offset of the page will be returned in `error_offset`.
+  ENOMEM     Ran out of memory trying to track private/shared state
+  ========== ===============================================================

[...]

+
+Set attributes for a range of offsets within a guest_memfd to
+KVM_MEMORY_ATTRIBUTE_PRIVATE to limit the specified guest_memfd backed
+memory range for guest_use. Even if KVM_CAP_GUEST_MEMFD_MMAP is

                         ^
                    guest use

+supported, after a successful call to set
+KVM_MEMORY_ATTRIBUTE_PRIVATE, the requested range will not be mappable
+into host userspace and will only be mappable by the guest.
+