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Thu, 29 Jun 2023 07:04:13 +0000 (GMT) Message-ID: Date: Thu, 29 Jun 2023 09:04:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] hw/ppc: Fix clock update drift Content-Language: en-US To: Nicholas Piggin , qemu-devel@nongnu.org Cc: qemu-ppc@nongnu.org, Daniel Henrique Barboza , =?UTF-8?Q?C=c3=a9dric_Le_Goater?= , David Gibson , Greg Kurz , Harsh Prateek Bora , qemu-stable@nongnu.org References: <20230629020713.327745-1-npiggin@gmail.com> From: Frederic Barrat In-Reply-To: <20230629020713.327745-1-npiggin@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: WbwLKTXrfw2ZEXxauGlUUxsx6vGrM35e X-Proofpoint-GUID: BsO7PP3tjXEAtJDgeAWTtWKC9N2bOPVo X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.591,FMLib:17.11.176.26 definitions=2023-06-28_14,2023-06-27_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 mlxlogscore=999 priorityscore=1501 lowpriorityscore=0 phishscore=0 clxscore=1011 malwarescore=0 adultscore=0 mlxscore=0 suspectscore=0 spamscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2305260000 definitions=main-2306290061 Received-SPF: pass client-ip=148.163.158.5; envelope-from=fbarrat@linux.ibm.com; helo=mx0b-001b2d01.pphosted.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.089, RCVD_IN_MSPIKE_H5=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 29/06/2023 04:07, Nicholas Piggin wrote: > The clock update logic reads the clock twice to compute the new clock > value, with a value derived from the later time subtracted from a value > derived from the earlier time. The delta causes time to be lost. > > This can ultimately result in time becoming unsynchronized between CPUs > and that can cause OS lockups, timeouts, watchdogs, etc. This can be > seen running a KVM guest (that causes lots of TB updates) on a powernv > SMP machine. > > Fix this by reading the clock once. > > Cc: qemu-stable@nongnu.org > Signed-off-by: Nicholas Piggin > --- Nice! It must have been a nightmare to debug. Do you know where that ATB spr comes from? I can't relate it to the ISA. Reviewed-by: Frederic Barrat > I also made a test case that can trigger this with kvm-unit-tests, but > it's been taking me a while to get that upstreamed. > > Thanks, > Nick > > hw/ppc/ppc.c | 33 +++++++++++++++++---------------- > 1 file changed, 17 insertions(+), 16 deletions(-) > > diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c > index 82e4408c5c..6233f43c01 100644 > --- a/hw/ppc/ppc.c > +++ b/hw/ppc/ppc.c > @@ -535,23 +535,24 @@ static inline void cpu_ppc_store_tb(ppc_tb_t *tb_env, uint64_t vmclk, > void cpu_ppc_store_tbl (CPUPPCState *env, uint32_t value) > { > ppc_tb_t *tb_env = env->tb_env; > + int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > uint64_t tb; > > - tb = cpu_ppc_get_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), tb_env->tb_offset); > + tb = cpu_ppc_get_tb(tb_env, clock, tb_env->tb_offset); > tb &= 0xFFFFFFFF00000000ULL; > - cpu_ppc_store_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), > - &tb_env->tb_offset, tb | (uint64_t)value); > + cpu_ppc_store_tb(tb_env, clock, &tb_env->tb_offset, tb | (uint64_t)value); > } > > static inline void _cpu_ppc_store_tbu(CPUPPCState *env, uint32_t value) > { > ppc_tb_t *tb_env = env->tb_env; > + int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > uint64_t tb; > > - tb = cpu_ppc_get_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), tb_env->tb_offset); > + tb = cpu_ppc_get_tb(tb_env, clock, tb_env->tb_offset); > tb &= 0x00000000FFFFFFFFULL; > - cpu_ppc_store_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), > - &tb_env->tb_offset, ((uint64_t)value << 32) | tb); > + cpu_ppc_store_tb(tb_env, clock, &tb_env->tb_offset, > + ((uint64_t)value << 32) | tb); > } > > void cpu_ppc_store_tbu (CPUPPCState *env, uint32_t value) > @@ -584,23 +585,24 @@ uint32_t cpu_ppc_load_atbu (CPUPPCState *env) > void cpu_ppc_store_atbl (CPUPPCState *env, uint32_t value) > { > ppc_tb_t *tb_env = env->tb_env; > + int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > uint64_t tb; > > - tb = cpu_ppc_get_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), tb_env->atb_offset); > + tb = cpu_ppc_get_tb(tb_env, clock, tb_env->atb_offset); > tb &= 0xFFFFFFFF00000000ULL; > - cpu_ppc_store_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), > - &tb_env->atb_offset, tb | (uint64_t)value); > + cpu_ppc_store_tb(tb_env, clock, &tb_env->atb_offset, tb | (uint64_t)value); > } > > void cpu_ppc_store_atbu (CPUPPCState *env, uint32_t value) > { > ppc_tb_t *tb_env = env->tb_env; > + int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > uint64_t tb; > > - tb = cpu_ppc_get_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), tb_env->atb_offset); > + tb = cpu_ppc_get_tb(tb_env, clock, tb_env->atb_offset); > tb &= 0x00000000FFFFFFFFULL; > - cpu_ppc_store_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), > - &tb_env->atb_offset, ((uint64_t)value << 32) | tb); > + cpu_ppc_store_tb(tb_env, clock, &tb_env->atb_offset, > + ((uint64_t)value << 32) | tb); > } > > uint64_t cpu_ppc_load_vtb(CPUPPCState *env) > @@ -622,14 +624,13 @@ void cpu_ppc_store_vtb(CPUPPCState *env, uint64_t value) > void cpu_ppc_store_tbu40(CPUPPCState *env, uint64_t value) > { > ppc_tb_t *tb_env = env->tb_env; > + int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL); > uint64_t tb; > > - tb = cpu_ppc_get_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), > - tb_env->tb_offset); > + tb = cpu_ppc_get_tb(tb_env, clock, tb_env->tb_offset); > tb &= 0xFFFFFFUL; > tb |= (value & ~0xFFFFFFUL); > - cpu_ppc_store_tb(tb_env, qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), > - &tb_env->tb_offset, tb); > + cpu_ppc_store_tb(tb_env, clock, &tb_env->tb_offset, tb); > } > > static void cpu_ppc_tb_stop (CPUPPCState *env)