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

[Reiji Watanabe]

On Sun, Nov 21, 2021 at 4:37 AM Marc Zyngier <maz at kernel.org> wrote:
>
> 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.

Shockingly, I somehow misunderstood what read_id_reg() did for GICv3...
I will use a different example for it.

Thanks,
Reiji