Commit f442ab50 authored by Axel Rasmussen's avatar Axel Rasmussen Committed by Andrew Morton
Browse files

mm: userfaultfd: document and enable new UFFDIO_POISON feature 

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: default avatarAxel Rasmussen <axelrasmussen@google.com>
Acked-by: default avatarPeter 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 8a13897f

Documentation/admin-guide/mm/userfaultfd.rst

+15 −0
Original line number Diff line number Diff line
@@ -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

========

include/uapi/linux/userfaultfd.h

+6 −3
Original line number Diff line number Diff line
@@ -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