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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: 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>
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@ -244,6 +244,21 @@ write-protected (so future writes will also result in a WP fault). These ioctls
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support a mode flag (``UFFDIO_COPY_MODE_WP`` or ``UFFDIO_CONTINUE_MODE_WP``
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respectively) to configure the mapping this way.
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Memory Poisioning Emulation
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---------------------------
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In response to a fault (either missing or minor), an action userspace can
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take to "resolve" it is to issue a ``UFFDIO_POISON``. This will cause any
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future faulters to either get a SIGBUS, or in KVM's case the guest will
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receive an MCE as if there were hardware memory poisoning.
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This is used to emulate hardware memory poisoning. Imagine a VM running on a
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machine which experiences a real hardware memory error. Later, we live migrate
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the VM to another physical machine. Since we want the migration to be
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transparent to the guest, we want that same address range to act as if it was
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still poisoned, even though it's on a new physical host which ostensibly
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doesn't have a memory error in the exact same spot.
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QEMU/KVM
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========
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@ -39,7 +39,8 @@
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UFFD_FEATURE_MINOR_SHMEM | \
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UFFD_FEATURE_EXACT_ADDRESS | \
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UFFD_FEATURE_WP_HUGETLBFS_SHMEM | \
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UFFD_FEATURE_WP_UNPOPULATED)
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UFFD_FEATURE_WP_UNPOPULATED | \
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UFFD_FEATURE_POISON)
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#define UFFD_API_IOCTLS \
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((__u64)1 << _UFFDIO_REGISTER | \
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(__u64)1 << _UFFDIO_UNREGISTER | \
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@ -49,12 +50,14 @@
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(__u64)1 << _UFFDIO_COPY | \
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(__u64)1 << _UFFDIO_ZEROPAGE | \
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(__u64)1 << _UFFDIO_WRITEPROTECT | \
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(__u64)1 << _UFFDIO_CONTINUE)
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(__u64)1 << _UFFDIO_CONTINUE | \
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(__u64)1 << _UFFDIO_POISON)
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#define UFFD_API_RANGE_IOCTLS_BASIC \
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((__u64)1 << _UFFDIO_WAKE | \
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(__u64)1 << _UFFDIO_COPY | \
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(__u64)1 << _UFFDIO_WRITEPROTECT | \
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(__u64)1 << _UFFDIO_CONTINUE | \
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(__u64)1 << _UFFDIO_WRITEPROTECT)
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(__u64)1 << _UFFDIO_POISON)
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/*
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* Valid ioctl command number range with this API is from 0x00 to
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