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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , Kevin Brodsky , linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 3/3] kselftest: mm: introduce alloc_isolated_mem() Message-ID: References: <20260907-fix_split-v5-3-822b810458bc@arm.com> <5c05b620-7a2f-453d-9725-fed4f536a019@kernel.org> <31418d0e-9745-4e8d-bc02-dbbd5cb9e193@kernel.org> <11a36d52-89a0-4f43-8a51-a4930e171ba0@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <11a36d52-89a0-4f43-8a51-a4930e171ba0@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: 8F05E80007 X-Stat-Signature: 6okyxwgayngsm44zfphfykai1iags3pr X-Rspamd-Server: rspam01 X-HE-Tag: 1789043693-645281 X-HE-Meta: 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 n7+qZJyf EQVYS1+ex0Tql9or+AdKSZsApS5iV5HI2z91lKav4NrSYkMTF8X7aTWSPCYu/1RsRQZLEdFeHNYxK8HmfiZr/hDZYlj/osUL1yOe/Ym4hzx+sHxAmnnftLEQrTDZNXd/c8jlKQLOoTK7MQUPXKTNxJKNWRfyvTVyQisp/+iYNFtY7erzMRDrouBtBZpRDZrKrxymjzOLbvxIYTQDthKb/Z0lSoxXhBbG7vz7PWGU5fXHREgXwDr5yvgASHch9Tz4VfjL5xXjrLlrjol0YBv2Rn2tsC/yonzNXqmWv Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Sep 10, 2026 at 02:25:40PM +0200, David Hildenbrand (Arm) wrote: > 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? True. I'll respin with your suggestion. Thanks! -- Sincerely, Yeoreum Yun