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Wed, 5 Feb 2025 17:01:02 GMT Received: from pps.reinject (localhost [127.0.0.1]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 44j8dnwsm6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 05 Feb 2025 17:01:02 +0000 Received: from iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 515H10V2013304; Wed, 5 Feb 2025 17:01:01 GMT Received: from bpf.uk.oracle.com (dhcp-10-154-48-77.vpn.oracle.com [10.154.48.77]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTP id 44j8dnwsh1-1; Wed, 05 Feb 2025 17:01:01 +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 v2 bpf] bpf/arena: fix softlockup in arena_map_free on 64k page kernel Date: Wed, 5 Feb 2025 17:00:59 +0000 Message-ID: <20250205170059.427458-1-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=2025-02-05_06,2025-02-05_03,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 phishscore=0 bulkscore=0 mlxlogscore=999 adultscore=0 suspectscore=0 mlxscore=0 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2501170000 definitions=main-2502050130 X-Proofpoint-GUID: 9BAve4wghOu_DoFwLgjFHh-aFFMatuPc X-Proofpoint-ORIG-GUID: 9BAve4wghOu_DoFwLgjFHh-aFFMatuPc 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 GUARD_SZ to PAGE_SIZE << 1 so that the division by 2 in bpf_arena_get_kern_vm_start() returns 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 Fixes: 317460317a02 ("bpf: Introduce bpf_arena.") Reported-by: Colm Harrington Suggested-by: Alexei Starovoitov 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..095a9554e1de 100644 --- a/kernel/bpf/arena.c +++ b/kernel/bpf/arena.c @@ -39,7 +39,7 @@ */ /* number of bytes addressable by LDX/STX insn with 16-bit 'off' field */ -#define GUARD_SZ (1ull << sizeof_field(struct bpf_insn, off) * 8) +#define GUARD_SZ round_up(1ull << sizeof_field(struct bpf_insn, off) * 8, PAGE_SIZE << 1) #define KERN_VM_SZ (SZ_4G + GUARD_SZ) struct bpf_arena {