On Mon, Jul 18, 2022 at 04:47:45AM -0700, Nadav Amit wrote:
> From: Nadav Amit <namit@xxxxxxxxxx>
>
> Introduce access-hints in userfaultfd. The expectation is that userspace
> would set access-hints when a page-fault occurred on a page and would
> not provide the access-hint on prefaulted memory. The exact behavior of
> the kernel in regard to the hints would not be part of userfaultfd api.
>
> At this time the use of the access-hint is only in setting access-bit
> similarly to the way it is done in do_set_pte(). In x86, currently PTEs
> are always marked as young, including prefetched ones. But on arm64,
> PTEs would be marked as old (when access bit is supported).
>
> If access hints are not enabled, the kernel would behave as if the
> access-hint was provided for backward compatibility.
>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
> Cc: Peter Xu <peterx@xxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
> ---
> fs/userfaultfd.c | 39 ++++++++++++++++++++++++++++----
> include/linux/userfaultfd_k.h | 1 +
> include/uapi/linux/userfaultfd.h | 20 +++++++++++++++-
> mm/internal.h | 13 +++++++++++
> mm/memory.c | 12 ----------
> mm/userfaultfd.c | 11 +++++++--
> 6 files changed, 77 insertions(+), 19 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 2ae24327beec..8d8792b27c53 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1708,13 +1708,21 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
> ret = -EINVAL;
> if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
> goto out;
> - if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
> + if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP|
> + UFFDIO_COPY_MODE_ACCESS_LIKELY))
> goto out;
>
> mode_wp = uffdio_copy.mode & UFFDIO_COPY_MODE_WP;
>
> uffd_flags = mode_wp ? UFFD_FLAGS_WP : UFFD_FLAGS_NONE;
>
> + if (ctx->features & UFFD_FEATURE_ACCESS_HINTS) {
> + if (uffdio_copy.mode & UFFDIO_COPY_MODE_ACCESS_LIKELY)
> + uffd_flags |= UFFD_FLAGS_ACCESS_LIKELY;
> + } else {
> + uffd_flags |= UFFD_FLAGS_ACCESS_LIKELY;
> + }
> +
This is quite a construct and it gets more complex in the following
patches. How about making it to a static inline function?
> if (mmget_not_zero(ctx->mm)) {
> ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
> uffdio_copy.len, &ctx->mmap_changing,
> @@ -1765,9 +1773,17 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
> if (ret)
> goto out;
> ret = -EINVAL;
> - if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
> + if (uffdio_zeropage.mode & ~(UFFDIO_ZEROPAGE_MODE_DONTWAKE|
> + UFFDIO_ZEROPAGE_MODE_ACCESS_LIKELY))
> goto out;
>
> + if (ctx->features & UFFD_FEATURE_ACCESS_HINTS) {
> + if (uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_ACCESS_LIKELY)
> + uffd_flags |= UFFD_FLAGS_ACCESS_LIKELY;
> + } else {
> + uffd_flags |= UFFD_FLAGS_ACCESS_LIKELY;
> + }
> +
> if (mmget_not_zero(ctx->mm)) {
> ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
> uffdio_zeropage.range.len,
--
Sincerely yours,
Mike.
