On Wed, Dec 04, 2024 at 09:43:25PM +0100, Alejandro Colomar wrote: > Hi Lorenzo, > > On Mon, Dec 02, 2024 at 04:58:29PM +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! A few minor comments below. > > > --- > > 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@xxxxxxxxxx > > > > v1: > > https://lore.kernel.org/all/20241129093205.8664-1-lorenzo.stoakes@xxxxxxxxxx > > > > man/man2/madvise.2 | 93 ++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 93 insertions(+) > > > > diff --git a/man/man2/madvise.2 b/man/man2/madvise.2 > > index 4f2210ee2..4cb5e7302 100644 > > --- a/man/man2/madvise.2 > > +++ b/man/man2/madvise.2 > > @@ -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 () > > We should specify the chapter in the manual: (2) Ack will fix. > > > +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 (), > > Same here. Will also fix :) > > > +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, > > Wouldn't it be better to say "valid only" instead of "only valid"? > > (Non-native speaker here, though.) Non-native speakers often pick up mistakes native speakers make because we're so used to the language we can decode 'clunky' sounding things and mistakenly write poorly as a result. You're correct, your version is almost certainly grammatically correct but far more importantly reads far more nicely! Will fix. > > Have a lovely night! > Alex Thanks! > > > +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 ) > > -- > > 2.47.1 > > -- > <https://www.alejandro-colomar.es/>
