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/20230707215540.2324998-1-axelrasmussen@google.com
Link: https://lkml.kernel.org/r/20230707215540.2324998-2-axelrasmussen@google.com
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: James Houghton <jthoughton@google.com>
Cc: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nadav Amit <namit@vmware.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 9 insertions, 6 deletions

diff --git a/mm/memory.c b/mm/memory.c
index ff19719da032..36b164ee9ffb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -860,8 +860,11 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 			return -EBUSY;
 		return -ENOENT;
 	} else if (is_pte_marker_entry(entry)) {
-		if (is_swapin_error_entry(entry) || userfaultfd_wp(dst_vma))
-			set_pte_at(dst_mm, addr, dst_pte, pte);
+		pte_marker marker = copy_pte_marker(entry, dst_vma);
+
+		if (marker)
+			set_pte_at(dst_mm, addr, dst_pte,
+				   make_pte_marker(marker));
 		return 0;
 	}
 	if (!userfaultfd_wp(dst_vma))
@@ -1502,7 +1505,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 			    !zap_drop_file_uffd_wp(details))
 				continue;
 		} else if (is_hwpoison_entry(entry) ||
-			   is_swapin_error_entry(entry)) {
+			   is_poisoned_swp_entry(entry)) {
 			if (!should_zap_cows(details))
 				continue;
 		} else {
@@ -3651,7 +3654,7 @@ static vm_fault_t pte_marker_clear(struct vm_fault *vmf)
 	 * none pte.  Otherwise it means the pte could have changed, so retry.
 	 *
 	 * This should also cover the case where e.g. the pte changed
-	 * quickly from a PTE_MARKER_UFFD_WP into PTE_MARKER_SWAPIN_ERROR.
+	 * quickly from a PTE_MARKER_UFFD_WP into PTE_MARKER_POISONED.
 	 * So is_pte_marker() check is not enough to safely drop the pte.
 	 */
 	if (pte_same(vmf->orig_pte, ptep_get(vmf->pte)))
@@ -3697,8 +3700,8 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
 		return VM_FAULT_SIGBUS;
 
 	/* Higher priority than uffd-wp when data corrupted */
-	if (marker & PTE_MARKER_SWAPIN_ERROR)
-		return VM_FAULT_SIGBUS;
+	if (marker & PTE_MARKER_POISONED)
+		return VM_FAULT_HWPOISON;
 
 	if (pte_marker_entry_uffd_wp(entry))
 		return pte_marker_handle_uffd_wp(vmf);