Hi Lorenzo, On Fri, Dec 06, 2024 at 11:34:18AM GMT, Lorenzo Stoakes wrote: > 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. > > Reviewed-by: Jann Horn <jannh@xxxxxxxxxx> > Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> Thanks for the updated patch. I had already applied v4: <https://lore.kernel.org/all/20241205104125.67518-1-lorenzo.stoakes@xxxxxxxxxx/T/#m7a891296e1ade7025569e3c3595b4f288135a7a9> > --- > v5: > * Prefer 'replaced' to 'cleared' when discussing existing mappings that have > MADV_GUARD_INSTALL applied to them, as suggested by Vlastimil. > * Included small changes Alejandro applied to patch. So I have now rebased v5 on top of the current tip of the branch, which results in a small patch containing just the wording fix: <https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=28c42e01fc175e50e38d> Have a lovely night! Alex > > v4: > * Reference function chapters as per Alejandro. > * Minor rewording as per Alejandro. > https://lore.kernel.org/all/20241205104125.67518-1-lorenzo.stoakes@xxxxxxxxxx > > v3: > * Don't describe SIGSEGV as a fatal signal as per Jann. > https://lore.kernel.org/all/20241202165829.72121-1-lorenzo.stoakes@xxxxxxxxxx > > 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@xxxxxxxxxx > > v1: > https://lore.kernel.org/all/20241129093205.8664-1-lorenzo.stoakes@xxxxxxxxxx > > man/man2/madvise.2 | 103 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 103 insertions(+) > > diff --git a/man/man2/madvise.2 b/man/man2/madvise.2 > index 0dd481d21..c9b4722db 100644 > --- a/man/man2/madvise.2 > +++ b/man/man2/madvise.2 > @@ -676,6 +676,101 @@ 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 > +those mappings will be replaced > +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 supported > +only 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 (2) > +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 (2), > +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, > +valid only 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 () > @@ -794,6 +889,14 @@ 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 ) > -- > 2.47.1 -- <https://www.alejandro-colomar.es/>
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