On 9/10/26 14:16, Yeoreum Yun wrote: >> On 9/10/26 13:30, Yeoreum Yun wrote: >>> >>> 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. > > It seems whether make a helper or testcase should write the code > properly in case of unwanted VMA merge. > > IMHO, instead of testcase write them all
So far I am aware of exactly one test case, which others do absolutely need this? -- Cheers, David
