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From: Axel Rasmussen <axelrasmussen@google.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Brian Geffon <bgeffon@google.com>,
	Christian Brauner <brauner@kernel.org>,
	David Hildenbrand <david@redhat.com>,
	Gaosheng Cui <cuigaosheng1@huawei.com>,
	Huang Ying <ying.huang@intel.com>,
	Hugh Dickins <hughd@google.com>,
	James Houghton <jthoughton@google.com>,
	"Jan Alexander Steffens (heftig)" <heftig@archlinux.org>,
	Jiaqi Yan <jiaqiyan@google.com>, Jonathan Corbet <corbet@lwn.net>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	"Mike Rapoport (IBM)" <rppt@kernel.org>,
	Muchun Song <muchun.song@linux.dev>,
	Nadav Amit <namit@vmware.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	Peter Xu <peterx@redhat.com>, Ryan Roberts <ryan.roberts@arm.com>,
	Shuah Khan <shuah@kernel.org>,
	Suleiman Souhlal <suleiman@google.com>,
	Suren Baghdasaryan <surenb@google.com>,
	"T.J. Alumbaugh" <talumbau@google.com>,
	Yu Zhao <yuzhao@google.com>, ZhangPeng <zhangpeng362@huawei.com>
Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org,
	Axel Rasmussen <axelrasmussen@google.com>
Subject: [PATCH v4 6/8] mm: userfaultfd: document and enable new UFFDIO_POISON feature
Date: Fri,  7 Jul 2023 14:55:38 -0700	[thread overview]
Message-ID: <20230707215540.2324998-7-axelrasmussen@google.com> (raw)
In-Reply-To: <20230707215540.2324998-1-axelrasmussen@google.com>

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.

Acked-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
 Documentation/admin-guide/mm/userfaultfd.rst | 15 +++++++++++++++
 include/uapi/linux/userfaultfd.h             |  9 ++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/mm/userfaultfd.rst b/Documentation/admin-guide/mm/userfaultfd.rst
index 7c304e432205..4349a8c2b978 100644
--- a/Documentation/admin-guide/mm/userfaultfd.rst
+++ b/Documentation/admin-guide/mm/userfaultfd.rst
@@ -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
 ========
 
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index b5f07eacc697..62151706c5a3 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/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
-- 
2.41.0.255.g8b1d071c50-goog


  parent reply	other threads:[~2023-07-07 21:56 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-07 21:55 [PATCH v4 0/8] add UFFDIO_POISON to simulate memory poisoning with UFFD Axel Rasmussen
2023-07-07 21:55 ` [PATCH v4 1/8] mm: make PTE_MARKER_SWAPIN_ERROR more general Axel Rasmussen
2023-07-08 15:00   ` Peter Xu
2023-07-09  1:08   ` Andrew Morton
2023-07-10 17:19     ` Axel Rasmussen
2023-07-10 21:59       ` Axel Rasmussen
2023-07-07 21:55 ` [PATCH v4 2/8] mm: userfaultfd: check for start + len overflow in validate_range Axel Rasmussen
2023-07-07 21:55 ` [PATCH v4 3/8] mm: userfaultfd: extract file size check out into a helper Axel Rasmussen
2023-07-07 21:55 ` [PATCH v4 4/8] mm: userfaultfd: add new UFFDIO_POISON ioctl Axel Rasmussen
2023-07-07 21:55 ` [PATCH v4 5/8] mm: userfaultfd: support UFFDIO_POISON for hugetlbfs Axel Rasmussen
2023-07-07 21:55 ` Axel Rasmussen [this message]
2023-07-07 21:55 ` [PATCH v4 7/8] selftests/mm: refactor uffd_poll_thread to allow custom fault handlers Axel Rasmussen
2023-07-08 15:02   ` Peter Xu
2023-07-10 17:08     ` Axel Rasmussen
2023-07-07 21:55 ` [PATCH v4 8/8] selftests/mm: add uffd unit test for UFFDIO_POISON Axel Rasmussen
2023-09-21 16:28   ` Ryan Roberts

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