On Wed, Oct 22, 2025, Ackerley Tng wrote:
> Ackerley Tng <[email protected]> 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. 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.
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
supported attributes than simply '1'. E.g. we have no plans to support
KVM_SET_MEMORY_ATTRIBUTES on guest_memfd, and so returning simply '1' creates an
unwanted and unnecessary dependency.
> @@ -1617,4 +1618,15 @@ struct kvm_pre_fault_memory {
> __u64 padding[5];
> };
>
> +/* Available with KVM_CAP_MEMORY_ATTRIBUTES2 */
> +#define KVM_SET_MEMORY_ATTRIBUTES2 _IOWR(KVMIO, 0xd6, struct
> kvm_memory_attributes2)
Please use the same literal number, 0xd2, as
#define KVM_SET_MEMORY_ATTRIBUTES _IOW(KVMIO, 0xd2, struct
kvm_memory_attributes)
The "final" ioctl number that userspace sees incorporates the directionality and
the size of the struct, i.e. KVM_SET_MEMORY_ATTRIBUTES and
KVM_SET_MEMORY_ATTRIBUTES2
are guaranteed to be distinct even if they both use 0xd2 as the "minor" number.
> +
> +struct kvm_memory_attributes2 {
> + __u64 address;
> + __u64 size;
> + __u64 attributes;
> + __u64 flags;
> + __u64 reserved[4];
Maybe be paranoid and reserve 12 u64s?
