mm: make PTE_MARKER_SWAPIN_ERROR more general

mm: make PTE_MARKER_SWAPIN_ERROR more general

Patch series "add UFFDIO_POISON to simulate memory poisoning with UFFD",
v4.

This series adds a new userfaultfd feature, UFFDIO_POISON. See commit 4
for a detailed description of the feature.

This patch (of 8):

Future patches will reuse PTE_MARKER_SWAPIN_ERROR to implement
UFFDIO_POISON, so make some various preparations for that:

First, rename it to just PTE_MARKER_POISONED.  The "SWAPIN" can be
confusing since we're going to re-use it for something not really related
to swap.  This can be particularly confusing for things like hugetlbfs,
which doesn't support swap whatsoever.  Also rename some various helper
functions.

Next, fix pte marker copying for hugetlbfs.  Previously, it would WARN on
seeing a PTE_MARKER_SWAPIN_ERROR, since hugetlbfs doesn't support swap.
But, since we're going to re-use it, we want it to go ahead and copy it
just like non-hugetlbfs memory does today.  Since the code to do this is
more complicated now, pull it out into a helper which can be re-used in
both places.  While we're at it, also make it slightly more explicit in
its handling of e.g.  uffd wp markers.

For non-hugetlbfs page faults, instead of returning VM_FAULT_SIGBUS for an
error entry, return VM_FAULT_HWPOISON.  For most cases this change doesn't
matter, e.g.  a userspace program would receive a SIGBUS either way.  But
for UFFDIO_POISON, this change will let KVM guests get an MCE out of the
box, instead of giving a SIGBUS to the hypervisor and requiring it to
somehow inject an MCE.

Finally, for hugetlbfs faults, handle PTE_MARKER_POISONED, and return
VM_FAULT_HWPOISON_LARGE in such cases.  Note that this can't happen today
because the lack of swap support means we'll never end up with such a PTE
anyway, but this behavior will be needed once such entries *can* show up
via UFFDIO_POISON.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Axel Rasmussen <[email protected]>
Acked-by: Peter Xu <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Brian Geffon <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Gaosheng Cui <[email protected]>
Cc: Huang, Ying <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: James Houghton <[email protected]>
Cc: Jan Alexander Steffens (heftig) <[email protected]>
Cc: Jiaqi Yan <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Mike Rapoport (IBM) <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Suleiman Souhlal <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: T.J. Alumbaugh <[email protected]>
Cc: Yu Zhao <[email protected]>
Cc: ZhangPeng <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>