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Mon, 19 Feb 2024 14:18:21 +0000 (GMT) Message-ID: <471ebba0055db993c8a3c57a290ce092358eb88b.camel@linux.ibm.com> Subject: Re: [PATCH v3 01/11] gdbstub: Support disablement in a multi-threaded process From: Ilya Leoshkevich To: Richard Henderson , Alex =?ISO-8859-1?Q?Benn=E9e?= , Laurent Vivier , Warner Losh Cc: Kyle Evans , Philippe =?ISO-8859-1?Q?Mathieu-Daud=E9?= , qemu-devel@nongnu.org Date: Mon, 19 Feb 2024 15:18:21 +0100 In-Reply-To: <2310cfb390c130baf709ac18328556ac0b713146.camel@linux.ibm.com> References: <20240216130817.369377-1-iii@linux.ibm.com> <20240216130817.369377-2-iii@linux.ibm.com> <8e3732d9-129c-4514-bb7a-d4c5bdca90dd@linaro.org> <2310cfb390c130baf709ac18328556ac0b713146.camel@linux.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.50.3 (3.50.3-1.fc39) MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: rJNP-vUHH2DqEk1CTXc43GTUzqnoOlJa X-Proofpoint-GUID: rJNP-vUHH2DqEk1CTXc43GTUzqnoOlJa X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-02-19_10,2024-02-19_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 mlxlogscore=999 adultscore=0 mlxscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 clxscore=1015 bulkscore=0 impostorscore=0 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2402190107 Received-SPF: pass client-ip=148.163.156.1; envelope-from=iii@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, 2024-02-19 at 14:05 +0100, Ilya Leoshkevich wrote: > On Sat, 2024-02-17 at 10:21 -1000, Richard Henderson wrote: > > On 2/16/24 03:05, Ilya Leoshkevich wrote: > > > The upcoming follow-fork-mode child support will require > > > disabling > > > gdbstub in the parent process, which may have multiple threads > > > (which > > > are represented as CPUs). > > >=20 > > > Loop over all CPUs in order to remove breakpoints and disable > > > single-step. Move the respective code into a separate function. > > >=20 > > > Signed-off-by: Ilya Leoshkevich > > > --- > > > =C2=A0 gdbstub/user.c | 19 +++++++++++++++---- > > > =C2=A0 1 file changed, 15 insertions(+), 4 deletions(-) > > >=20 > > > diff --git a/gdbstub/user.c b/gdbstub/user.c > > > index 14918d1a217..e17f7ece908 100644 > > > --- a/gdbstub/user.c > > > +++ b/gdbstub/user.c > > > @@ -356,16 +356,27 @@ int gdbserver_start(const char > > > *port_or_path) > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -1; > > > =C2=A0 } > > > =C2=A0=20 > > > +static void disable_gdbstub(void) > > > +{ > > > +=C2=A0=C2=A0=C2=A0 CPUState *cpu; > > > + > > > +=C2=A0=C2=A0=C2=A0 close(gdbserver_user_state.fd); > > > +=C2=A0=C2=A0=C2=A0 gdbserver_user_state.fd =3D -1; > > > +=C2=A0=C2=A0=C2=A0 CPU_FOREACH(cpu) { > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cpu_breakpoint_remove_all= (cpu, BP_GDB); > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* no cpu_watchpoint_remo= ve_all for user-mode */ > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 cpu_single_step(cpu, 0); > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 tb_flush(cpu); > >=20 > > You only need to flush once.=C2=A0 The cpu argument is used to determin= e > > if we can perform the=20 > > flush immediately or need to queue it. >=20 > I thought we needed to flush jump caches on all CPUs, but I see now > that do_tb_flush() already does this, so this loop is unnecessarily > quadratic. >=20 > Btw, shouldn't do_tb_flush() have cpu as a local variable, and not as > a parameter? Never mind, the dummy parameter is needed for usage with async_safe_run_on_cpu(). [...]