On Wed, Aug 02, 2023 at 08:55:43AM -0700, Jing Zhang wrote:
> > > +#define ARM64_FEATURE_ID_SPACE_SIZE (3 * 8 * 8)
> > > +
> > > +struct feature_id_writable_masks {
> > > + __u64 mask[ARM64_FEATURE_ID_SPACE_SIZE];
> > > +};
> >
> > This UAPI is rather difficult to extend in the future. We may need to
> > support describing the masks of multiple ranges of registers in the
> > future. I was thinking something along the lines of:
> >
> > enum reg_mask_range_idx {
> > FEATURE_ID,
> > };
> >
> > struct reg_mask_range {
> > __u64 idx;
> > __u64 *masks;
> > __u64 rsvd[6];
> > };
> >
> Since have the way to map sysregs encoding to the index in the mask
> array, we can extend the UAPI by just adding a size field in struct
> feature_id_writable_masks like below:
> struct feature_id_writable_masks {
> __u64 size;
> __u64 mask[ARM64_FEATURE_ID_SPACE_SIZE];
> };
> The 'size' field can be used as input for the size of 'mask' array and
> output for the number of masks actually read in.
> This way, we can freely add more ranges without breaking anything in userspace.
> WDYT?
Sorry, 'index' is a bit overloaded in this context. The point I was
trying to get across is that we might want to describe a completely
different range of registers than the feature ID registers in the
future. Nonetheless, we shouldn't even presume the shape of future
extensions to the ioctl.
struct reg_mask_range {
__u64 addr; /* pointer to mask array */
__u64 rsvd[7];
};
Then in KVM we should require ::rsvd be zero and fail the ioctl
otherwise.
--
Thanks,
Oliver
