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Thu, 2 Apr 2026 06:59:41 +0000 (GMT) Message-ID: Date: Thu, 2 Apr 2026 12:29:40 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Sayali Patil Subject: Re: [PATCH v3 09/13] selftests/mm: skip uffd-wp-mremap if UFFD write-protect is unsupported To: Andrew Morton , Shuah Khan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Ritesh Harjani Cc: David Hildenbrand , Zi Yan , Michal Hocko , Oscar Salvador , Lorenzo Stoakes , Dev Jain , Liam.Howlett@oracle.com, linuxppc-dev@lists.ozlabs.org References: <5bc0fe27cdd316ef6f776bf9b52b6c0de4bef54f.1774591179.git.sayalip@linux.ibm.com> Content-Language: en-IN In-Reply-To: <5bc0fe27cdd316ef6f776bf9b52b6c0de4bef54f.1774591179.git.sayalip@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=Fdo6BZ+6 c=1 sm=1 tr=0 ts=69ce13e6 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=Ikd4Dj_1AAAA:8 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=X_KCTOUB8Lo47miopUAA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: _PKXl_TFP9s8I2DLHw3-X6DosxfFph5V X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDAyMDA1OSBTYWx0ZWRfXzClFUfw9yQ1K mS1M24R0Wl1zjNTReKRTJXi2ZL5bYLTAsQSMc5GAR3FHWkenF84klAAgrMAEPzc80g28QfQskxE kWC3BytAk24o48Hzfg8mGnWx8PCFm2RyXBGsh9ozkhvQsg4Ha2kKNCYgrx8db8GOKHMzhGica6t TQY+K0IZuKUVLC+MrvYDVxct3tUxWaI4/guWSCvRORoePZmhgCmftrNhzNVlJ8OX2CisyQ+ZlKQ JkbLT3kxj/3lOB0KqshddGiDUdntaa0FpABnMDDd1QZyoynVQyBSbbhQaebUWosirEeL1YI6jGq 6yUKt9b0q0MEWN0pQhSfNUjManVAsgf0hTro1BtJGBuAGo14DegAmZt9mCNJkm7VMx2YEAZ+ECZ snVINASbaK3rX3JD6i09xD7z3AsFx2nvH91B/V0vwOujEJJqzWKNKsvIvk8XLG+otjTEJiR+4s7 v/bq1Jma+BkcXbz+2Pw== X-Proofpoint-GUID: sJCAzj54eSGJ2M_geFmpHo6yBe2LRsGe X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-02_01,2026-04-01_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1015 bulkscore=0 suspectscore=0 priorityscore=1501 adultscore=0 malwarescore=0 phishscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2604020059 On 27/03/26 12:46, Sayali Patil wrote: > The uffd-wp-mremap test requires the UFFD_FEATURE_PAGEFAULT_FLAG_WP > capability. On systems where userfaultfd write-protect is > not supported, uffd_register() fails and the test reports failures. > > Check for the required feature at startup and skip the test when the > UFFD_FEATURE_PAGEFAULT_FLAG_WP capability is not present, > preventing false failures on unsupported configurations. > > Before patch: > running ./uffd-wp-mremap > ------------------------ > [INFO] detected THP size: 256 KiB > [INFO] detected THP size: 512 KiB > [INFO] detected THP size: 1024 KiB > [INFO] detected THP size: 2048 KiB > [INFO] detected hugetlb page size: 2048 KiB > [INFO] detected hugetlb page size: 1048576 KiB > 1..24 > [RUN] test_one_folio(size=65536, private=false, swapout=false, > hugetlb=false) > not ok 1 uffd_register() failed > [RUN] test_one_folio(size=65536, private=true, swapout=false, > hugetlb=false) > not ok 2 uffd_register() failed > [RUN] test_one_folio(size=65536, private=false, swapout=true, > hugetlb=false) > not ok 3 uffd_register() failed > [RUN] test_one_folio(size=65536, private=true, swapout=true, > hugetlb=false) > not ok 4 uffd_register() failed > [RUN] test_one_folio(size=262144, private=false, swapout=false, > hugetlb=false) > not ok 5 uffd_register() failed > [RUN] test_one_folio(size=524288, private=false, swapout=false, > hugetlb=false) > not ok 6 uffd_register() failed > . > . > . > Bail out! 24 out of 24 tests failed > Totals: pass:0 fail:24 xfail:0 xpass:0 skip:0 error:0 > [FAIL] > not ok 1 uffd-wp-mremap # exit=1 > > After patch: > running ./uffd-wp-mremap > ------------------------ > 1..0 # SKIP uffd-wp feature not supported > [SKIP] > ok 1 uffd-wp-mremap # SKIP > > Acked-by: Zi Yan > Acked-by: David Hildenbrand (Arm) > Signed-off-by: Sayali Patil > --- > tools/testing/selftests/mm/uffd-wp-mremap.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/tools/testing/selftests/mm/uffd-wp-mremap.c b/tools/testing/selftests/mm/uffd-wp-mremap.c > index 17186d4a4147..6edbd09f0ca6 100644 > --- a/tools/testing/selftests/mm/uffd-wp-mremap.c > +++ b/tools/testing/selftests/mm/uffd-wp-mremap.c > @@ -19,6 +19,17 @@ static size_t thpsizes[20]; > static int nr_hugetlbsizes; > static size_t hugetlbsizes[10]; > > +static void check_uffd_wp_feature_supported(void) > +{ > + uint64_t features; > + > + if (uffd_get_features(&features) && errno == ENOENT) > + ksft_exit_skip("failed to get available features (%d)\n", errno); > + > + if (!(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP)) > + ksft_exit_skip("uffd-wp feature not supported\n"); > +} > + > static int detect_thp_sizes(size_t sizes[], int max) > { > int count = 0; > @@ -336,6 +347,8 @@ int main(int argc, char **argv) > struct thp_settings settings; > int i, j, plan = 0; > > + check_uffd_wp_feature_supported(); > + > pagesize = getpagesize(); > nr_thpsizes = detect_thp_sizes(thpsizes, ARRAY_SIZE(thpsizes)); > nr_hugetlbsizes = detect_hugetlb_page_sizes(hugetlbsizes, AI review question: > commit 22914640356d1eaf4e0a8a8b13ad71911d12db50 > Author: Sayali Patil > selftests/mm: skip uffd-wp-mremap if UFFD write-protect is unsupported > This commit adds a check at startup to verify if the userfaultfd > write-protect capability is present. It skips the test instead of reporting> false failures on unsupported configurations. > > diff --git a/tools/testing/selftests/mm/uffd-wp-mremap.c b/tools/testing/selftests/mm/uffd-wp-mremap.c> > index 17186d4a4147..6edbd09f0ca6 100644 > > --- a/tools/testing/selftests/mm/uffd-wp-mremap.c > > +++ b/tools/testing/selftests/mm/uffd-wp-mremap.c > > @@ -19,6 +19,17 @@ static size_t thpsizes[20]; > > static int nr_hugetlbsizes; > > static size_t hugetlbsizes[10]; > > > +static void check_uffd_wp_feature_supported(void) > > +{ > > + uint64_t features; > > + > > + if (uffd_get_features(&features) && errno == ENOENT) > > + ksft_exit_skip("failed to get available features (%d)\n", errno); > If uffd_get_features() fails but errno is something other than ENOENT (for> example, EPERM when unprivileged userfaultfd is disabled), this check will > evaluate to false and execution will continue.> > + > > + if (!(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP)) > Could this evaluate uninitialized stack memory? > If uffd_get_features() fails and is bypassed by the previous check, the > features variable will remain uninitialized. This might cause the test to > falsely pass or fail depending on whatever data happens to be on the stack.> Should we initialize features to zero or exit on all uffd_get_features() > failures instead? > > + ksft_exit_skip("uffd-wp feature not supported\n"); > > +} Yes,If uffd_get_features() fails with an error other than ENOENT, the features variable would remain uninitialized, which could lead to undefined behavior in the subsequent check. I will fix this in the next patch version. Thanks, Sayali