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Tue, 4 Feb 2025 09:24:59 GMT Received: from pps.reinject (localhost [127.0.0.1]) by iadpaimrmta03.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 44j8fnrgpe-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 04 Feb 2025 09:24:58 +0000 Received: from iadpaimrmta03.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta03.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 5149MlAH005579; Tue, 4 Feb 2025 09:24:58 GMT Received: from bpf.uk.oracle.com (dhcp-10-175-201-234.vpn.oracle.com [10.175.201.234]) by iadpaimrmta03.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 44j8fnrgnx-1; Tue, 04 Feb 2025 09:24:58 +0000 From: Alan Maguire To: ast@kernel.org Cc: daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, bpf@vger.kernel.org, Alan Maguire , Colm Harrington Subject: [PATCH bpf] bpf/arena: fix softlockup in arena_map_free on 64k page kernel Date: Tue, 4 Feb 2025 09:24:55 +0000 Message-ID: <20250204092455.3693003-1-alan.maguire@oracle.com> X-Mailer: git-send-email 2.43.5 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-02-04_04,2025-01-31_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 malwarescore=0 phishscore=0 mlxlogscore=999 bulkscore=0 suspectscore=0 adultscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2501170000 definitions=main-2502040075 X-Proofpoint-GUID: oyTJeb4mh1J9ix5T6gCwr9zkA0Plrlkn X-Proofpoint-ORIG-GUID: oyTJeb4mh1J9ix5T6gCwr9zkA0Plrlkn X-Patchwork-Delegate: bpf@iogearbox.net On an aarch64 kernel with CONFIG_PAGE_SIZE_64KB=y (64k pages), arena_htab tests cause a segmentation fault and soft lockup. $ sudo ./test_progs -t arena_htab Caught signal #11! Stack trace: ./test_progs(crash_handler+0x1c)[0x7bd4d8] linux-vdso.so.1(__kernel_rt_sigreturn+0x0)[0xffffb34a0968] ./test_progs[0x420f74] ./test_progs(htab_lookup_elem+0x3c)[0x421090] ./test_progs[0x421320] ./test_progs[0x421bb8] ./test_progs(test_arena_htab+0x40)[0x421c14] ./test_progs[0x7bda84] ./test_progs(main+0x65c)[0x7bf670] /usr/lib64/libc.so.6(+0x2caa0)[0xffffb31ecaa0] /usr/lib64/libc.so.6(__libc_start_main+0x98)[0xffffb31ecb78] ./test_progs(_start+0x30)[0x41b4f0] Message from syslogd@bpfol9aarch64 at Feb 4 08:50:09 ... kernel:watchdog: BUG: soft lockup - CPU#1 stuck for 26s! [kworker/u8:4:7589] The same failure is not observed with 4k pages on aarch64. Investigating further, it turns out arena_map_free() was calling apply_to_existing_page_range() with the address returned by bpf_arena_get_kern_vm_start(). If this address is not page-aligned - as is the case for a 64k page kernel - we wind up calling apply_to_pte_range() with that unaligned address. The problem is apply_to_pte_range() implicitly assumes that the addr passed in is page-aligned, specifically in this loop: do { if (create || !pte_none(ptep_get(pte))) { err = fn(pte++, addr, data); if (err) break; } } while (addr += PAGE_SIZE, addr != end); If addr is _not_ page-aligned, it will never equal end exactly. One solution is to round up the address returned by bpf_arena_get_kern_vm_start() to a page-aligned value. With that change in place the test passes: $ sudo ./test_progs -t arena_htab Summary: 1/1 PASSED, 1 SKIPPED, 0 FAILED Reported-by: Colm Harrington Signed-off-by: Alan Maguire --- kernel/bpf/arena.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c index 870aeb51d70a..07395c55833e 100644 --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -54,7 +54,7 @@ struct bpf_arena { u64 bpf_arena_get_kern_vm_start(struct bpf_arena *arena) { - return arena ? (u64) (long) arena->kern_vm->addr + GUARD_SZ / 2 : 0; + return arena ? (u64) round_up((long) arena->kern_vm->addr + GUARD_SZ / 2, PAGE_SIZE) : 0; } u64 bpf_arena_get_user_vm_start(struct bpf_arena *arena)