> > On 9/10/26 13:30, Yeoreum Yun wrote: > > >> On 9/10/26 13:22, Yeoreum Yun wrote: > > >>> > > >>> As I mentioned in my previous reply, what I’m trying to prevent here is > > >>> a failure when checking, immediately after memory allocation, > > >>> that a specific vm_flag is not set. > > >>> > > >>> Yes, I agree that this could have been a problem even before > > >>> the internal changes to memalign(). An unwanted VMA merge could already > > >>> occur at the time of memory allocation. > > >>> > > >>> So what I’m trying to avoid is a test failure where, due to such an > > >>> unexpected VMA merge during allocation, the subsequent check that > > >>> a specific vm_flag is not present fails. > > >> Which is only a guard-region marker problem? > > > > > > Yes. so if we remove ASSERT_FALSE(check_vmflag_guard(ptr)), TBH > > > we don't need this patch unless other usage comes up to prevent unwanted > > > VMA merge. > > > > > > Would it be better to drop ASSERT_FALSE(check_vmflag_guard(ptr)) in > > > guard test? > > > > I guess there is value in asserting that not all VMAs by accident start > > with an over-indication of maybe having guard pages, which is why Lorenzo > > added that check :) > > > > But I think even alloc_isolated_mem() is wrong in that regard: if the > > original VMA gets merged, we could inherit the guard-marker, no? > > True. I overlooked guard bit is sticky. > > > > > Maybe the following would be good enough? > > > > diff --git a/tools/testing/selftests/mm/guard-regions.c > > b/tools/testing/selftests/mm/guard-regions.c > > index 5c8ec3ca75d7d..791bf6a68b9e6 100644 > > --- a/tools/testing/selftests/mm/guard-regions.c > > +++ b/tools/testing/selftests/mm/guard-regions.c > > @@ -2257,10 +2257,20 @@ 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); > > + /* Reserve a 10 page region with 1 page space to both sides. */ > > + ptr = mmap_(self, variant, NULL, 12 * page_size, PROT_NONE, 0, 0); > > ASSERT_NE(ptr, MAP_FAILED); > > > > + /* Map a new region that is guaranteed to not get merged in any > > way. */ > > + ptr = mmap_(self, variant | MAP_FIXED, ptr + pagesize, 10 * > > page_size, > > + PROT_READ | PROT_WRITE, 0, 0); > > + ASSERT_EQ(ptr, ptr + pagesize); > > + > > + /* Clean up the excess pages left and right. */ > > + munmap(ptr, pagesize); > > + munmap(ptr + 11, pagesize); > > + ptr + = pagesize; > > + > > /* We shouldn't yet see a guard flag. */ > > ASSERT_FALSE(check_vmflag_guard(ptr)); > > > > -- > > Cheers, > > It's enough but alloc_isolated_mem() could be modified to allocate with > PROT_NONE first and then change the prot.
Ah, but if merged with PROT_NONE | GURAD still problem... Hmm.. might above enough. -- Sincerely, Yeoreum Yun
