[RFC PATCH v3 03/29] KVM: arm64: Introduce struct id_reg_info

[Marc Zyngier]

On Fri, 19 Nov 2021 04:47:53 +0000,
Reiji Watanabe <reijiw at google.com> wrote:
> 
> I am going to add the following comment. Does it look clear enough for you ?
> 
>         /*
>          * This is an optional ID register specific validation function.
>          * When userspace tries to set the ID register, arm64_check_features()
>          * will check if the requested value indicates any features that cannot
>          * be supported by KVM on the host.  But, some ID register fields need
>          * a special checking and this function can be used for such fields.
>          * e.g. KVM_CREATE_DEVICE must be used to configure GICv3 for a guest.
>          * ID_AA64PFR0_EL1.GIC shouldn't be set to 1 unless GICv3 is configured.

There is no such requirement. GICv3 has a compatibility interface, and
although KVM doesn't make use of it, there is no reason not to expose
that GICv3 exists on the CPU even if not using it. Even more, this has
been the case forever, and making this change now would probably break
migration.

	M.

-- 
Without deviation from the norm, progress is not possible.