On 17/10/2025 21:11, Ackerley Tng wrote:
Introduce a "version 2" of KVM_SET_MEMORY_ATTRIBUTES to support returning information back to userspace.
This new ioctl and structure will, in a later patch, be shared as a guest_memfd ioctl, where the padding in the new kvm_memory_attributes2 structure will be for writing the response from the guest_memfd ioctl to userspace.
A new ioctl is necessary for these reasons:
KVM_SET_MEMORY_ATTRIBUTES is currently a write-only ioctl and does not allow userspace to read fields. There's nothing in code (yet?) that validates this, but using _IOWR for consistency would be prudent.
KVM_SET_MEMORY_ATTRIBUTES, when used as a guest_memfd ioctl, will need an additional field to provide userspace with more error details.
Alternatively, a completely new ioctl could be defined, unrelated to KVM_SET_MEMORY_ATTRIBUTES, but using the same ioctl number and struct for the vm and guest_memfd ioctls streamlines the interface for userspace. In addition, any memory attributes, implemented on the vm or guest_memfd ioctl, can be easily shared with the other.
Suggested-by: Sean Christopherson seanjc@google.com Signed-off-by: Ackerley Tng ackerleytng@google.com
Documentation/virt/kvm/api.rst | 32 +++++++++++++++++++++++++++++++ include/uapi/linux/kvm.h | 12 ++++++++++++ virt/kvm/kvm_main.c | 35 +++++++++++++++++++++++++++++++--- 3 files changed, 76 insertions(+), 3 deletions(-)
[...]
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 52f6000ab0208..c300e38c7c9cd 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h
[...]
@@ -5366,15 +5375,35 @@ static long kvm_vm_ioctl(struct file *filp, } #endif /* CONFIG_HAVE_KVM_IRQ_ROUTING */ #ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES
- case KVM_SET_MEMORY_ATTRIBUTES2: case KVM_SET_MEMORY_ATTRIBUTES: {
struct kvm_memory_attributes attrs;
struct kvm_memory_attributes2 attrs;unsigned long size;if (ioctl == KVM_SET_MEMORY_ATTRIBUTES) {/** Fields beyond struct kvm_userspace_memory_region shouldn't be* accessed, but avoid leaking kernel memory in case of a bug.*/memset(&mem, 0, sizeof(mem));
s/mem/attrs/g
size = sizeof(struct kvm_set_memory_attributes);} else {size = sizeof(struct kvm_set_memory_attributes2);
s/kvm_set_memory_attributes/kvm_memory_attributes/ (on both sizeof lines above and in the SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD macro).
}/* Ensure the common parts of the two structs are identical. */SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(slot);SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(flags);SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(guest_phys_addr);SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(memory_size);SANITY_CHECK_MEMORY_ATTRIBUTES_FIELD(userspace_addr);
The fields are: * address * size * attributes * flags
The list you've got appears to match struct kvm_userspace_memory_region - copy/paste error?
Thanks, Steve
r = -ENOTTY; if (!vm_memory_attributes) goto out; r = -EFAULT;
if (copy_from_user(&attrs, argp, sizeof(attrs)))
if (copy_from_user(&attrs, argp, size)) goto out;r = kvm_vm_ioctl_set_mem_attributes(kvm, &attrs);