From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 736B0273D8 for ; Thu, 14 Sep 2023 22:16:27 +0000 (UTC) Received: from out-212.mta1.migadu.com (out-212.mta1.migadu.com [IPv6:2001:41d0:203:375::d4]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D5A1D2D4E for ; Thu, 14 Sep 2023 15:16:26 -0700 (PDT) Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1694729784; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NlndV5xoe1+caV++nDpyLure5nzdczZq8WEUsVPta1Q=; b=gi9M0KHI+HQy6+2TbWDRS5KmpRJiYtLLyAVr8k7mwq8hUPllz+TykhlZ6eWschVaoffO2U sTdJ+Iwu3O5LESxXQsULIjQ9yT5SYrPyYFwHo1nFFIpJME1xtI69yljHpmZjMEHmGdRa8I RzCj/sDROLEvUZLEQLHeclq6GEFGnPY= Date: Thu, 14 Sep 2023 15:16:18 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next] bpf: Charge modmem for struct_ops trampoline Content-Language: en-US To: Song Liu Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kernel-team@meta.com, bpf@vger.kernel.org References: <20230913222632.3312183-1-song@kernel.org> <208035ba-3016-c9ba-92e4-fe2cee797ca8@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 9/14/23 2:28 PM, Song Liu wrote: > On Thu, Sep 14, 2023 at 2:14 PM Martin KaFai Lau wrote: >> >> On 9/13/23 3:26 PM, Song Liu wrote: >>> Current code charges modmem for regular trampoline, but not for struct_ops >>> trampoline. Add bpf_jit_[charge|uncharge]_modmem() to struct_ops so the >>> trampoline is charged in both cases. >>> >>> Signed-off-by: Song Liu >>> --- >>> kernel/bpf/bpf_struct_ops.c | 13 +++++++++++-- >>> 1 file changed, 11 insertions(+), 2 deletions(-) >>> >>> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c >>> index fdc3e8705a3c..ea6ca87a2ed9 100644 >>> --- a/kernel/bpf/bpf_struct_ops.c >>> +++ b/kernel/bpf/bpf_struct_ops.c >>> @@ -615,7 +615,10 @@ static void __bpf_struct_ops_map_free(struct bpf_map *map) >>> if (st_map->links) >>> bpf_struct_ops_map_put_progs(st_map); >>> bpf_map_area_free(st_map->links); >>> - bpf_jit_free_exec(st_map->image); >>> + if (st_map->image) { >>> + bpf_jit_free_exec(st_map->image); >>> + bpf_jit_uncharge_modmem(PAGE_SIZE); >>> + } >>> bpf_map_area_free(st_map->uvalue); >>> bpf_map_area_free(st_map); >>> } >>> @@ -657,6 +660,7 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr) >>> struct bpf_struct_ops_map *st_map; >>> const struct btf_type *t, *vt; >>> struct bpf_map *map; >>> + int ret; >>> >>> st_ops = bpf_struct_ops_find_value(attr->btf_vmlinux_value_type_id); >>> if (!st_ops) >>> @@ -681,6 +685,12 @@ static struct bpf_map *bpf_struct_ops_map_alloc(union bpf_attr *attr) >>> st_map->st_ops = st_ops; >>> map = &st_map->map; >>> >>> + ret = bpf_jit_charge_modmem(PAGE_SIZE); >>> + if (ret) { >>> + __bpf_struct_ops_map_free(map); >>> + return ERR_PTR(ret); >>> + } >> >> >> This just came to my mind when reading it again. >> >> It will miss a bpf_jit_uncharge_modmem() if the bpf_jit_alloc_exec() at a few >> lines below did fail (meaning st_map->image is NULL). It is because the >> __bpf_struct_ops_map_free() only uncharge if st_map->image is not NULL. > > Indeed. This is a problem. > >> >> How above moving the bpf_jit_alloc_exec() to here (immediately after >> bpf_jit_charge_modem succeeded). Like, >> >> st_map->image = bpf_jit_alloc_exec(PAGE_SIZE); >> if (!st_map->image) { >> bpf_jit_uncharge_modmem(PAGE_SIZE); >> __bpf_struct_ops_map_free(map); >> return ERR_PTR(-ENOMEM); >> } >> >> Then there is also no need to test 'if (st_map->image)' in >> __bpf_struct_ops_map_free(). > > I think we still need this test for uncharge, no? You are right, somehow I thought the above bpf_jit_charge_modmem's failure path could directly use the bpf_map_area_free() instead of __bpf_struct_ops_map_free(). Agree, lets keep it consistent, call __bpf_struct_ops_map_free() on all failure paths and keep the 'if (st_map->image)' check there. Thanks.