On Fri, Sep 11, 2026 at 01:59:31PM +0100, Lorenzo Stoakes (ARM) wrote: > On Fri, Sep 11, 2026 at 01:35:34PM +0100, Yeoreum Yun wrote: > > check_vmflag_guard() uses /proc/self/smaps to retrieve the VMA flags, > > but this can fail if the mapping is merged with an adjacent VMA. > > > > To avoid this potential failure, first allocate a temporary region with > > extra pages at both ends, unmap it, and then map the test region within > > the temporary address range, leaving an unmapped page on each side to > > prevent VMA merging. > > > > Signed-off-by: Yeoreum Yun <[email protected]> > > --- > > tools/testing/selftests/mm/guard-regions.c | 14 ++++++++++++-- > > 1 file changed, 12 insertions(+), 2 deletions(-) > > > > diff --git a/tools/testing/selftests/mm/guard-regions.c > > b/tools/testing/selftests/mm/guard-regions.c > > index 5c8ec3ca75d7..a28a57d34e97 100644 > > --- a/tools/testing/selftests/mm/guard-regions.c > > +++ b/tools/testing/selftests/mm/guard-regions.c > > @@ -2257,8 +2257,18 @@ TEST_F(guard_regions, smaps) > > char *ptr, *ptr2; > > int i; > > > > - /* Map a region. */ > > - ptr = mmap_(self, variant, NULL, 10 * page_size, PROT_READ | > > PROT_WRITE, 0, 0); > > + /* Try to Map a region. */ > > Map -> map > > > + ptr = mmap_(self, variant, NULL, 12 * page_size, PROT_READ | > > PROT_WRITE, 0, 0); > > Should be PROT_NONE otherwise it'll merge with the below.
It doesn't matter. since this memory is unmapped and then second map at ptr + page_size. IOW, though the first one is merged, it unammped and then the second is allocated at ptr + page_size, it wouldn't be merged: after unmap: [existing VMA][ 12 pages ][existing VMA] second: [exiting VMA] [hole (page)] [ 10 pages (for test)] [hole (page)] [existing VMA] Am I missing something? -- Sincerely, Yeoreum Yun
