The patch titled
Subject: mm: userfaultfd: document and enable new UFFDIO_POISON feature
has been added to the -mm mm-unstable branch. Its filename is
mm-userfaultfd-document-and-enable-new-uffdio_poison-feature.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-userfaultfd-document-and-enable-new-uffdio_poison-feature.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Subject: mm: userfaultfd: document and enable new UFFDIO_POISON feature
Date: Fri, 7 Jul 2023 14:55:38 -0700
Update the userfaultfd API to advertise this feature as part of feature
flags and supported ioctls (returned upon registration).
Add basic documentation describing the new feature.
Link: https://lkml.kernel.org/r/20230707215540.2324998-7-axelrasmussen@xxxxxxxxxx
Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Brian Geffon <bgeffon@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Gaosheng Cui <cuigaosheng1@xxxxxxxxxx>
Cc: Huang, Ying <ying.huang@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Jan Alexander Steffens (heftig) <heftig@xxxxxxxxxxxxx>
Cc: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Cc: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: T.J. Alumbaugh <talumbau@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: ZhangPeng <zhangpeng362@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/mm/userfaultfd.rst | 15 +++++++++++++++
include/uapi/linux/userfaultfd.h | 9 ++++++---
2 files changed, 21 insertions(+), 3 deletions(-)
--- a/Documentation/admin-guide/mm/userfaultfd.rst~mm-userfaultfd-document-and-enable-new-uffdio_poison-feature
+++ a/Documentation/admin-guide/mm/userfaultfd.rst
@@ -244,6 +244,21 @@ write-protected (so future writes will a
support a mode flag (``UFFDIO_COPY_MODE_WP`` or ``UFFDIO_CONTINUE_MODE_WP``
respectively) to configure the mapping this way.
+Memory Poisioning Emulation
+---------------------------
+
+In response to a fault (either missing or minor), an action userspace can
+take to "resolve" it is to issue a ``UFFDIO_POISON``. This will cause any
+future faulters to either get a SIGBUS, or in KVM's case the guest will
+receive an MCE as if there were hardware memory poisoning.
+
+This is used to emulate hardware memory poisoning. Imagine a VM running on a
+machine which experiences a real hardware memory error. Later, we live migrate
+the VM to another physical machine. Since we want the migration to be
+transparent to the guest, we want that same address range to act as if it was
+still poisoned, even though it's on a new physical host which ostensibly
+doesn't have a memory error in the exact same spot.
+
QEMU/KVM
========
--- a/include/uapi/linux/userfaultfd.h~mm-userfaultfd-document-and-enable-new-uffdio_poison-feature
+++ a/include/uapi/linux/userfaultfd.h
@@ -39,7 +39,8 @@
UFFD_FEATURE_MINOR_SHMEM | \
UFFD_FEATURE_EXACT_ADDRESS | \
UFFD_FEATURE_WP_HUGETLBFS_SHMEM | \
- UFFD_FEATURE_WP_UNPOPULATED)
+ UFFD_FEATURE_WP_UNPOPULATED | \
+ UFFD_FEATURE_POISON)
#define UFFD_API_IOCTLS \
((__u64)1 << _UFFDIO_REGISTER | \
(__u64)1 << _UFFDIO_UNREGISTER | \
@@ -49,12 +50,14 @@
(__u64)1 << _UFFDIO_COPY | \
(__u64)1 << _UFFDIO_ZEROPAGE | \
(__u64)1 << _UFFDIO_WRITEPROTECT | \
- (__u64)1 << _UFFDIO_CONTINUE)
+ (__u64)1 << _UFFDIO_CONTINUE | \
+ (__u64)1 << _UFFDIO_POISON)
#define UFFD_API_RANGE_IOCTLS_BASIC \
((__u64)1 << _UFFDIO_WAKE | \
(__u64)1 << _UFFDIO_COPY | \
+ (__u64)1 << _UFFDIO_WRITEPROTECT | \
(__u64)1 << _UFFDIO_CONTINUE | \
- (__u64)1 << _UFFDIO_WRITEPROTECT)
+ (__u64)1 << _UFFDIO_POISON)
/*
* Valid ioctl command number range with this API is from 0x00 to
_
Patches currently in -mm which might be from axelrasmussen@xxxxxxxxxx are
mm-make-pte_marker_swapin_error-more-general.patch
mm-userfaultfd-check-for-start-len-overflow-in-validate_range.patch
mm-userfaultfd-extract-file-size-check-out-into-a-helper.patch
mm-userfaultfd-add-new-uffdio_poison-ioctl.patch
mm-userfaultfd-support-uffdio_poison-for-hugetlbfs.patch
mm-userfaultfd-document-and-enable-new-uffdio_poison-feature.patch
selftests-mm-refactor-uffd_poll_thread-to-allow-custom-fault-handlers.patch
selftests-mm-add-uffd-unit-test-for-uffdio_poison.patch
