On Thu, Oct 23, 2025, Ackerley Tng wrote:
Sean Christopherson seanjc@google.com writes:
On Wed, Oct 22, 2025, Ackerley Tng wrote:
Ackerley Tng ackerleytng@google.com writes:
Found another issue with KVM_CAP_MEMORY_ATTRIBUTES2.
KVM_CAP_MEMORY_ATTRIBUTES2 was defined to do the same thing as KVM_CAP_MEMORY_ATTRIBUTES, but that's wrong since KVM_CAP_MEMORY_ATTRIBUTES2 should indicate the presence of KVM_SET_MEMORY_ATTRIBUTES2 and struct kvm_memory_attributes2.
No? If no attributes are supported, whether or not KVM_SET_MEMORY_ATTRIBUTES2 exists is largely irrelevant.
That's true.
We can even provide the same -ENOTTY errno by checking that _any_ attributes are supported, i.e. so that doing KVM_SET_MEMORY_ATTRIBUTES2 on KVM without any support whatsoever fails in the same way that KVM with code support but no attributes fails.
IIUC KVM_SET_MEMORY_ATTRIBUTES doesn't fail with -ENOTTY now when there are no valid attributes.
Even if there's no valid attributes (as in kvm_supported_mem_attributes() returns 0), it's possible to call KVM_SET_MEMORY_ATTRIBUTES with .attributes set to 0, which will be a no-op, but will return 0.
I think this is kind of correct behavior since .attributes = 0 is actually a valid expression for "I want this range to be shared", and for a VM that doesn't support private memory, it's a valid expression.
The other way that there are "no attributes" would be if there are no /VM/ attributes, in which case KVM_SET_MEMORY_ATTRIBUTES, sent to as a vm ioctl, will return -ENOTTY.
Ya, this is what I was trying to say with "_any_ attributes are supported". I.e. by "any" I meant "any attributes in KVM for VMs vs. gmems", not "any attributes for this specific VM/gmem instance".
In other words, I don't see why it can't do both. Even if we can't massage the right errno, I would much rather KVM_SET_MEMORY_ATTRIBUTES2 enumerate the set of
Did you mean KVM_CAP_MEMORY_ATTRIBUTES2 in the line above?
Doh, yes.