@@ -676,6 +676,91 @@ or secret memory regions created using
Note that with
.BR MADV_POPULATE_WRITE ,
the process can be killed at any moment when the system runs out of memory.
+.TP
+.BR MADV_GUARD_INSTALL " (since Linux 6.13)"
+Install a lightweight guard region into the range specified by
+.I addr
+and
+.IR size ,
+causing any read or write in the range to result in a
+.B SIGSEGV
+signal being raised.
+.IP
+If the region maps memory pages they will be cleared as part of the operation,
+though if
+.B MADV_GUARD_INSTALL
+is applied to regions containing pre-existing lightweight guard regions,
+they are left in place.
+.IP
+This operation is only supported for writable anonymous private mappings which
+have not been mlock'd.
+An
+.B EINVAL
+error is returned if it is attempted on any other kind of mapping.
+.IP
+This operation is more efficient than mapping a new region of memory
+.BR PROT_NONE ,
+as it does not require the establishment of new mappings,
+instead regions of an existing mapping simply have their page tables
+manipulated to establish the desired behavior.
+No additional memory is used.
+.IP
+Lightweight guard regions remain on fork
+(except for any parts which have had
+.B MADV_WIPEONFORK
+applied to them),
+and are not removed by
+.BR MADV_DONTNEED ,
+.BR MADV_FREE ,
+.BR MADV_PAGEOUT ,
+or
+.BR MADV_COLD .
+.IP
+Attempting to
+.BR mlock ()
+lightweight guard regions will fail,
+as will
+.B MADV_POPULATE_READ
+or
+.BR MADV_POPULATE_WRITE .
+.IP
+If the mapping has its attributes changed,
+or is split or partially unmapped,
+any existing guard regions remain in place
+(except if they are unmapped).
+.IP
+If a mapping is moved using
+.BR mremap (),
+lightweight guard regions are moved with it.
+.IP
+Lightweight guard regions are removed when unmapped,
+on process teardown,
+or when the
+.B MADV_GUARD_REMOVE
+operation is applied to them.
+.TP
+.BR MADV_GUARD_REMOVE " (since Linux 6.13)"
+Remove any lightweight guard regions which exist in the range specified by
+.I addr
+and
+.IR size .
+.IP
+All mappings in the range other than lightweight guard regions are left in place
+(including mlock'd mappings).
+The operation is,
+however,
+only valid for writable anonymous private mappings,
+returning an
+.B EINVAL
+error otherwise.
+.IP
+When lightweight guard regions are removed,
+they act as empty regions of the containing mapping.
+Since only writable anonymous private mappings are supported,
+they therefore become zero-fill-on-demand pages.
+.IP
+If any transparent huge pages are encountered in the operation,
+they are left in place.
.SH RETURN VALUE
On success,
.BR madvise ()
@@ -787,6 +872,14 @@ or
or secret memory regions created using
.BR memfd_secret(2) .
.TP
+.B EINVAL
+.I advice
+is
+.B MADV_GUARD_INSTALL
+or
+.BR MADV_GUARD_REMOVE ,
+but the specified address range contains an unsupported mapping.
+.TP
.B EIO
(for
.BR MADV_WILLNEED )
Lightweight guard region support has been added to Linux 6.13, which adds MADV_GUARD_INSTALL and MADV_GUARD_REMOVE flags to the madvise() system call. Therefore, update the manpage for madvise() and describe these operations. Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> --- v3: * Don't describe SIGSEGV as a fatal signal as per Jann. v2: * Updated to use semantic newlines as suggested by Alejandro. * Avoided emboldening parens as suggested by Alejandro. * One very minor grammatical fix. https://lore.kernel.org/all/20241129155943.85215-1-lorenzo.stoakes@oracle.com v1: https://lore.kernel.org/all/20241129093205.8664-1-lorenzo.stoakes@oracle.com man/man2/madvise.2 | 93 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 93 insertions(+) -- 2.47.1