[RFC PATCH v2 18/28] KVM: arm64: Introduce KVM_CAP_ARM_ID_REG_WRITABLE capability

[Reiji Watanabe]

On Thu, Nov 4, 2021 at 9:41 AM Oliver Upton <oupton at google.com> wrote:
>
> On Tue, Nov 02, 2021 at 11:25:10PM -0700, Reiji Watanabe wrote:
> > Introduce a new capability KVM_CAP_ARM_ID_REG_WRITABLE to indicate
> > that ID registers are writable by userspace.
> >
> > Signed-off-by: Reiji Watanabe <reijiw at google.com>
> > ---
> >  Documentation/virt/kvm/api.rst | 8 ++++++++
> >  arch/arm64/kvm/arm.c           | 1 +
> >  include/uapi/linux/kvm.h       | 1 +
> >  3 files changed, 10 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index a6729c8cf063..f7dfb5127310 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -7265,3 +7265,11 @@ The argument to KVM_ENABLE_CAP is also a bitmask, and must be a subset
> >  of the result of KVM_CHECK_EXTENSION.  KVM will forward to userspace
> >  the hypercalls whose corresponding bit is in the argument, and return
> >  ENOSYS for the others.
> > +
> > +8.35 KVM_CAP_ARM_ID_REG_WRITABLE
> > +--------------------------------
>
> ID registers are technically already writable, KVM just rejects any
> value other than what it derives from sanitising the host ID registers.
> I agree that the nuance being added warrants a KVM_CAP, as it informs
> userspace it can deliberately configure ID registers with a more limited
> value than what KVM returns.
>
> KVM_CAP_ARM_ID_REG_CONFIGURABLE maybe? Naming is hard :)

Thank you for the suggestion.  Yes, that sounds better.
I will change the name as you suggested.

Regards,
Reiji