Re: [PATCH v10 01/12] KVM: arm64: Allow userspace to get the writable masks for feature ID registers

[Cornelia Huck <cohuck@redhat.com>]

On Wed, Sep 20 2023, Oliver Upton <oliver.upton@linux.dev> wrote:

> From: Jing Zhang <jingzhangos@google.com>
>
> While the Feature ID range is well defined and pretty large, it isn't
> inconceivable that the architecture will eventually grow some other
> ranges that will need to similarly be described to userspace.
>
> Add a VM ioctl to allow userspace to get writable masks for feature ID
> registers in below system register space:
> op0 = 3, op1 = {0, 1, 3}, CRn = 0, CRm = {0 - 7}, op2 = {0 - 7}
> This is used to support mix-and-match userspace and kernels for writable
> ID registers, where userspace may want to know upfront whether it can
> actually tweak the contents of an idreg or not.
>
> Add a new capability (KVM_CAP_ARM_SUPPORTED_FEATURE_ID_RANGES) that
> returns a bitmap of the valid ranges, which can subsequently be
> retrieved, one at a time by setting the index of the set bit as the
> range identifier.
>
> Suggested-by: Marc Zyngier <maz@kernel.org>
> Suggested-by: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: Jing Zhang <jingzhangos@google.com>

<process>I think you need to add your s-o-b here.</process>

> ---
>  arch/arm64/include/asm/kvm_host.h |  2 +
>  arch/arm64/include/uapi/asm/kvm.h | 32 +++++++++++++++
>  arch/arm64/kvm/arm.c              | 10 +++++
>  arch/arm64/kvm/sys_regs.c         | 66 +++++++++++++++++++++++++++++++
>  include/uapi/linux/kvm.h          |  2 +
>  5 files changed, 112 insertions(+)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>