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Howlett" , Vlastimil Babka , Mike Rapoport , Michal Hocko , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrei Vagin Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam05 X-Stat-Signature: ti5zfnfstru5qzx7wffw7mirkijgsgek X-Rspam-User: X-Rspamd-Queue-Id: E838C1C000B X-HE-Tag: 1761799231-388528 X-HE-Meta: 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 wjxSoJru JUE7XoVkMP61qH+Zz+mDcX9omsiqXJu2EEuX1IxZqoxFaKManaTY4/LhTTIHQIysH9GD6iXurzKU5LtJHA8Z1E4HXJyK9l7JiqPT6QsfDCe6AhMeM/6+k9vs+Qb9PKE75pSDvsYoBsHkmYaojVFxNEZQubclH19hyXgb5ag5FoptbYHqb0JxmFLAYhcHAepUnXRdvw6Mqpz2my+JljNAz1xkPrs8doD2w74csnhEwWFg/amqtl/fzUQ57KQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 29, 2025 at 9:51=E2=80=AFAM Lorenzo Stoakes wrote: > > Assert that we observe guard regions appearing in /proc/$pid/smaps as > expected, and when split/merge is performed too (with expected sticky > behaviour). > > Also add handling for file systems which don't sanely handle mmap() VMA > merging so we don't incorrectly encounter a test failure in this situatio= n. > > Signed-off-by: Lorenzo Stoakes Reviewed-by: Suren Baghdasaryan > --- > tools/testing/selftests/mm/guard-regions.c | 120 +++++++++++++++++++++ > tools/testing/selftests/mm/vm_util.c | 5 + > tools/testing/selftests/mm/vm_util.h | 1 + > 3 files changed, 126 insertions(+) > > diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/s= elftests/mm/guard-regions.c > index 8dd81c0a4a5a..a9be11e03a6a 100644 > --- a/tools/testing/selftests/mm/guard-regions.c > +++ b/tools/testing/selftests/mm/guard-regions.c > @@ -94,6 +94,7 @@ static void *mmap_(FIXTURE_DATA(guard_regions) * self, > case ANON_BACKED: > flags |=3D MAP_PRIVATE | MAP_ANON; > fd =3D -1; > + offset =3D 0; > break; > case SHMEM_BACKED: > case LOCAL_FILE_BACKED: > @@ -260,6 +261,54 @@ static bool is_buf_eq(char *buf, size_t size, char c= hr) > return true; > } > > +/* > + * Some file systems have issues with merging due to changing merge-sens= itive > + * parameters in the .mmap callback, and prior to .mmap_prepare being > + * implemented everywhere this will now result in an unexpected failure = to > + * merge (e.g. - overlayfs). > + * > + * Perform a simple test to see if the local file system suffers from th= is, if > + * it does then we can skip test logic that assumes local file system me= rging is > + * sane. > + */ > +static bool local_fs_has_sane_mmap(FIXTURE_DATA(guard_regions) * self, > + const FIXTURE_VARIANT(guard_regions) *= variant) > +{ > + const unsigned long page_size =3D self->page_size; > + char *ptr, *ptr2; > + struct procmap_fd procmap; > + > + if (variant->backing !=3D LOCAL_FILE_BACKED) > + return true; > + > + /* Map 10 pages. */ > + ptr =3D mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PR= OT_WRITE, 0, 0); > + if (ptr =3D=3D MAP_FAILED) > + return false; > + /* Unmap the middle. */ > + munmap(&ptr[5 * page_size], page_size); > + > + /* Map again. */ > + ptr2 =3D mmap_(self, variant, &ptr[5 * page_size], page_size, PRO= T_READ | PROT_WRITE, > + MAP_FIXED, 5 * page_size); > + > + if (ptr2 =3D=3D MAP_FAILED) > + return false; > + > + /* Now make sure they all merged. */ > + if (open_self_procmap(&procmap) !=3D 0) > + return false; > + if (!find_vma_procmap(&procmap, ptr)) > + return false; > + if (procmap.query.vma_start !=3D (unsigned long)ptr) > + return false; > + if (procmap.query.vma_end !=3D (unsigned long)ptr + 10 * page_siz= e) > + return false; > + close_procmap(&procmap); > + > + return true; > +} > + > FIXTURE_SETUP(guard_regions) > { > self->page_size =3D (unsigned long)sysconf(_SC_PAGESIZE); > @@ -2138,4 +2187,75 @@ TEST_F(guard_regions, pagemap_scan) > ASSERT_EQ(munmap(ptr, 10 * page_size), 0); > } > > +TEST_F(guard_regions, smaps) > +{ > + const unsigned long page_size =3D self->page_size; > + struct procmap_fd procmap; > + char *ptr, *ptr2; > + int i; > + > + /* Map a region. */ > + ptr =3D mmap_(self, variant, NULL, 10 * page_size, PROT_READ | PR= OT_WRITE, 0, 0); > + ASSERT_NE(ptr, MAP_FAILED); > + > + /* We shouldn't yet see a guard flag. */ > + ASSERT_FALSE(check_vmflag_guard(ptr)); > + > + /* Install a single guard region. */ > + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_INSTALL), 0); > + > + /* Now we should see a guard flag. */ > + ASSERT_TRUE(check_vmflag_guard(ptr)); > + > + /* > + * Removing the guard region should not change things because we = simply > + * cannot accurately track whether a given VMA has had all of its= guard > + * regions removed. > + */ > + ASSERT_EQ(madvise(ptr, page_size, MADV_GUARD_REMOVE), 0); > + ASSERT_TRUE(check_vmflag_guard(ptr)); > + > + /* Install guard regions throughout. */ > + for (i =3D 0; i < 10; i++) { > + ASSERT_EQ(madvise(&ptr[i * page_size], page_size, MADV_GU= ARD_INSTALL), 0); > + /* We should always see the guard region flag. */ > + ASSERT_TRUE(check_vmflag_guard(ptr)); > + } > + > + /* Split into two VMAs. */ > + ASSERT_EQ(munmap(&ptr[4 * page_size], page_size), 0); > + > + /* Both VMAs should have the guard flag set. */ > + ASSERT_TRUE(check_vmflag_guard(ptr)); > + ASSERT_TRUE(check_vmflag_guard(&ptr[5 * page_size])); > + > + /* > + * If the local file system is unable to merge VMAs due to having > + * unusual characteristics, there is no point in asserting merge > + * behaviour. > + */ > + if (!local_fs_has_sane_mmap(self, variant)) { > + TH_LOG("local filesystem does not support sane merging sk= ipping merge test"); > + return; > + } > + > + /* Map a fresh VMA between the two split VMAs. */ > + ptr2 =3D mmap_(self, variant, &ptr[4 * page_size], page_size, > + PROT_READ | PROT_WRITE, MAP_FIXED, 4 * page_size); > + ASSERT_NE(ptr2, MAP_FAILED); > + > + /* > + * Check the procmap to ensure that this VMA merged with the adja= cent > + * two. The guard region flag is 'sticky' so should not preclude > + * merging. > + */ > + ASSERT_EQ(open_self_procmap(&procmap), 0); > + ASSERT_TRUE(find_vma_procmap(&procmap, ptr)); > + ASSERT_EQ(procmap.query.vma_start, (unsigned long)ptr); > + ASSERT_EQ(procmap.query.vma_end, (unsigned long)ptr + 10 * page_s= ize); > + ASSERT_EQ(close_procmap(&procmap), 0); > + /* And, of course, this VMA should have the guard flag set. */ > + ASSERT_TRUE(check_vmflag_guard(ptr)); > +} > + > TEST_HARNESS_MAIN > diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftes= ts/mm/vm_util.c > index e33cda301dad..605cb58ea5c3 100644 > --- a/tools/testing/selftests/mm/vm_util.c > +++ b/tools/testing/selftests/mm/vm_util.c > @@ -449,6 +449,11 @@ bool check_vmflag_pfnmap(void *addr) > return check_vmflag(addr, "pf"); > } > > +bool check_vmflag_guard(void *addr) > +{ > + return check_vmflag(addr, "gu"); > +} > + > bool softdirty_supported(void) > { > char *addr; > diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftes= ts/mm/vm_util.h > index 26c30fdc0241..a8abdf414d46 100644 > --- a/tools/testing/selftests/mm/vm_util.h > +++ b/tools/testing/selftests/mm/vm_util.h > @@ -98,6 +98,7 @@ int uffd_register_with_ioctls(int uffd, void *addr, uin= t64_t len, > unsigned long get_free_hugepages(void); > bool check_vmflag_io(void *addr); > bool check_vmflag_pfnmap(void *addr); > +bool check_vmflag_guard(void *addr); > int open_procmap(pid_t pid, struct procmap_fd *procmap_out); > int query_procmap(struct procmap_fd *procmap); > bool find_vma_procmap(struct procmap_fd *procmap, void *address); > -- > 2.51.0 >