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mm: userfaultfd: document and enable new UFFDIO_POISON feature

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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@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>
This commit is contained in:
Axel Rasmussen 2023-07-07 14:55:38 -07:00 committed by Andrew Morton
parent 8a13897fb0
commit f442ab50f5
2 changed files with 21 additions and 3 deletions
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15
Documentation/admin-guide/mm/userfaultfd.rst
View file

@ -244,6 +244,21 @@ write-protected (so future writes will also result in a WP fault). These ioctls
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
========

9
include/uapi/linux/userfaultfd.h
View file

@ -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