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Rao" Subject: Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions To: Masami Hiramatsu , Peter Zijlstra Cc: alexei.starovoitov@gmail.com, alyssa.milburn@intel.com, andrew.cooper3@citrix.com, hjl.tools@gmail.com, joao@overdrivepizza.com, jpoimboe@redhat.com, keescook@chromium.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, mbenes@suse.cz, ndesaulniers@google.com, rostedt@goodmis.org, samitolvanen@google.com, x86@kernel.org References: <20220224145138.952963315@infradead.org> <20220224151322.892372059@infradead.org> <20220228150705.aab2d654b973109bab070ffe@kernel.org> <20220228232513.GH11184@worktop.programming.kicks-ass.net> In-Reply-To: <20220228232513.GH11184@worktop.programming.kicks-ass.net> User-Agent: astroid/4d6b06ad (https://github.com/astroidmail/astroid) Message-Id: <1646153789.geynpzwbid.naveen@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: hSaf28dtkpqCPMAz-BXMHBVMHSVq3rzO X-Proofpoint-GUID: z-RcKJuXdoxf9LRt2EKAbxB3uRZk35GH Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-03-01_07,2022-02-26_01,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 impostorscore=0 mlxscore=0 spamscore=0 priorityscore=1501 malwarescore=0 lowpriorityscore=0 clxscore=1011 mlxlogscore=777 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2201110000 definitions=main-2203010089 X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL, SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, Peter Zijlstra wrote: > On Mon, Feb 28, 2022 at 03:07:05PM +0900, Masami Hiramatsu wrote: >> Hi Peter, >>=20 >> So, instead of this change, can you try below? >> This introduce the arch_adjust_kprobe_addr() and use it in the kprobe_ad= dr() >> so that it can handle the case that user passed the probe address in=20 >> _text+OFFSET format. >=20 > It works a little... at the very least it still needs > arch_kprobe_on_func_entry() allowing offset 4. >=20 > But looking at this, we've got: >=20 > kprobe_on_func_entry(addr, sym, offset) > _kprobe_addr(addr, sym, offset) > if (sym) > addr =3D kprobe_lookup_name() > =3D kallsyms_lookup_name() > arch_adjust_kprobe_addr(addr+offset) > skip_endbr() > kallsyms_loopup_size_offset(addr, ...) > kallsyms_lookup_size_offset(addr, NULL, &offset) > arch_kprobe_on_func_entry(offset) >=20 > Which is _3_ kallsyms lookups and 3 weak/arch hooks. >=20 > Surely we can make this a little more streamlined? The below seems to > work. >=20 > I think with a little care and testing it should be possible to fold all > the magic of PowerPC's kprobe_lookup_name() into this one hook as well, > meaning we can get rid of kprobe_lookup_name() entirely. Naveen? This is timely. I've been looking at addressing a similar set of issues=20 on powerpc: http://lkml.kernel.org/r/cover.1645096227.git.naveen.n.rao@linux.vnet.ibm.c= om >=20 > This then gets us down to a 1 kallsyms call and 1 arch hook. Hmm? I was going to propose making _kprobe_addr() into a weak function in=20 place of kprobe_lookup_name() in response to Masami in the other thread,=20 but this is looking better. >=20 > --- > arch/powerpc/kernel/kprobes.c | 34 +++++++++++++++--------- > arch/x86/kernel/kprobes/core.c | 17 ++++++++++++ > include/linux/kprobes.h | 3 +- > kernel/kprobes.c | 56 ++++++++++++++++++++++++++++++++++= ------- > 4 files changed, 87 insertions(+), 23 deletions(-) I will take a closer look at this tomorrow and revert. Thanks, - Naveen