On Fri, Nov 29, 2024 at 01:35:01PM +0100, Alejandro Colomar wrote: > Hi Lorenzo, > > On Fri, Nov 29, 2024 at 09:32:05AM +0000, 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. > > > > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> > > Thanks for the patch. Please see some comments below. Ack will fix up and respin! > > Have a lovely day! You too! Thanks for taking the time to look :) > Alex > > > --- > > man/man2/madvise.2 | 81 ++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 81 insertions(+) > > > > diff --git a/man/man2/madvise.2 b/man/man2/madvise.2 > > index 4f2210ee2..e539fefe4 100644 > > --- a/man/man2/madvise.2 > > +++ b/man/man2/madvise.2 > > @@ -676,6 +676,79 @@ 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 fatal > > +.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. > > Please use semantic newlines. See man-pages(7): > > $ MANWIDTH=72 man man-pages | sed -n '/Use semantic newlines/,/^$/p'; > Use semantic newlines > In the source of a manual page, new sentences should be started > on new lines, long sentences should be split into lines at > clause breaks (commas, semicolons, colons, and so on), and long > clauses should be split at phrase boundaries. This convention, > sometimes known as "semantic newlines", makes it easier to see > the effect of patches, which often operate at the level of in‐ > dividual sentences, clauses, or phrases. > > > > +.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 > > +.B 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 any are unmapped). > > +.IP > > +If a mapping is moved using > > +.BR mremap() , > > The "()" should not be bold. They should go with the ','. > > > +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 +860,14 @@ 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/>
