Re: [RFC PATCH v2 35/47] userfaultfd: require UFFD_FEATURE_EXACT_ADDRESS when using HugeTLB HGM

[James Houghton]

On Thu, Dec 22, 2022 at 4:47 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> On Fri, Oct 21, 2022 at 04:36:51PM +0000, James Houghton wrote:
> > @@ -1990,6 +1990,17 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
> >               ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
> >  #ifndef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
> >       uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS_HGM;
> > +#else
> > +
> > +     ret = -EINVAL;
> > +     if ((uffdio_api.features & UFFD_FEATURE_MINOR_HUGETLBFS_HGM) &&
> > +         !(uffdio_api.features & UFFD_FEATURE_EXACT_ADDRESS))
>
> This check needs to be done upon "features" or "ctx_features", rather than
> "uffdio_api.features".  The latter is the one we'll report to the user only.

Ack, thanks Peter. I'm going to drop this patch given the API change
(switching to MADV_SPLIT).

- James