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b=eYs29H7RAOHNZT0L0BMbol/UZyu9DcDD234BWc5lS2vdbiCWm4sAPXpEAVwk4LDKKBcUTSkdUZBcp4Inaw8xwK/HuKkG82BdbPAl7nR3NXcF1CGglFzxPIiWJxPOBWoV/5fGQRLrQUQwK7a3YO2s5Zh/z3gF5WpOhYko3X/juMA= Received: from BYAPR21MB1688.namprd21.prod.outlook.com (2603:10b6:a02:bf::26) by SN7PR21MB3858.namprd21.prod.outlook.com (2603:10b6:806:2ed::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.6411.0; Thu, 11 May 2023 23:11:08 +0000 Received: from BYAPR21MB1688.namprd21.prod.outlook.com ([fe80::a4f7:2466:97b5:bd31]) by BYAPR21MB1688.namprd21.prod.outlook.com ([fe80::a4f7:2466:97b5:bd31%4]) with mapi id 15.20.6411.007; Thu, 11 May 2023 23:11:08 +0000 From: "Michael Kelley (LINUX)" To: Peter Zijlstra , Wei Liu CC: "ltykernel@gmail.com" , "bigeasy@linutronix.de" , Mark Rutland , "maz@kernel.org" , "catalin.marinas@arm.com" , "will@kernel.org" , "chenhuacai@kernel.org" , "kernel@xen0n.name" , "hca@linux.ibm.com" , "gor@linux.ibm.com" , "agordeev@linux.ibm.com" , "borntraeger@linux.ibm.com" , "svens@linux.ibm.com" , "pbonzini@redhat.com" , "wanpengli@tencent.com" , "vkuznets@redhat.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "jgross@suse.com" , "boris.ostrovsky@oracle.com" , "daniel.lezcano@linaro.org" , KY Srinivasan , Haiyang Zhang , Dexuan Cui , "rafael@kernel.org" , "longman@redhat.com" , "boqun.feng@gmail.com" , "pmladek@suse.com" , "senozhatsky@chromium.org" , "rostedt@goodmis.org" , "john.ogness@linutronix.de" , "juri.lelli@redhat.com" , "vincent.guittot@linaro.org" , "dietmar.eggemann@arm.com" , "bsegall@google.com" , "mgorman@suse.de" , "bristot@redhat.com" , "vschneid@redhat.com" , "jstultz@google.com" , "sboyd@kernel.org" , "linux-kernel@vger.kernel.org" , "loongarch@lists.linux.dev" , "linux-s390@vger.kernel.org" , "kvm@vger.kernel.org" , "linux-hyperv@vger.kernel.org" , "linux-pm@vger.kernel.org" Subject: RE: [RFC][PATCH 7/9] x86/tsc: Provide sched_clock_noinstr() Thread-Topic: [RFC][PATCH 7/9] x86/tsc: Provide sched_clock_noinstr() Thread-Index: AQHZgfVJgXDGJCXHgkicklmkIOtQvK9Q6JGAgAAdu4CABILIgIAALlKQ Date: Thu, 11 May 2023 23:11:07 +0000 Message-ID: References: <20230508211951.901961964@infradead.org> <20230508213147.853677542@infradead.org> <20230508214419.GA2053935@hirez.programming.kicks-ass.net> <20230511202351.GE2296992@hirez.programming.kicks-ass.net> In-Reply-To: <20230511202351.GE2296992@hirez.programming.kicks-ass.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ActionId=d7099938-895d-4a93-9f19-d91b36949928;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_ContentBits=0;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=true;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Method=Standard;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=Internal;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2023-05-11T23:09:38Z;MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR21MB1688.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 8cb8579c-9eb8-4f8b-3720-08db527500b3 X-MS-Exchange-CrossTenant-originalarrivaltime: 11 May 2023 23:11:07.9398 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: +GoYwVlFKF1eTKEtvHfgB9ND2IU8cVR/a1YxfF5Dc7PTur7Zm3hrhK63QWeSpuIw+aR2/knGpFZPwbB+NFJwpIOYDlfRqRBSPJa31TDJEoY= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR21MB3858 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra Sent: Thursday, May 11, 2023 1:= 24 PM >=20 > On Mon, May 08, 2023 at 11:30:43PM +0000, Wei Liu wrote: > > On Mon, May 08, 2023 at 11:44:19PM +0200, Peter Zijlstra wrote: > > > On Mon, May 08, 2023 at 11:19:58PM +0200, Peter Zijlstra wrote: > > > > > > > --- a/drivers/clocksource/hyperv_timer.c > > > > +++ b/drivers/clocksource/hyperv_timer.c > > > > @@ -408,9 +408,9 @@ static u64 notrace read_hv_clock_tsc_cs( > > > > return read_hv_clock_tsc(); > > > > } > > > > > > > > -static u64 notrace read_hv_sched_clock_tsc(void) > > > > +static u64 noinstr read_hv_sched_clock_tsc(void) > > > > { > > > > - return (read_hv_clock_tsc() - hv_sched_clock_offset) * > > > > + return (hv_read_tsc_page(hv_get_tsc_page()) - hv_sched_clock_offs= et) * > > > > (NSEC_PER_SEC / HV_CLOCK_HZ); > > > > } > > > > > > > > --- a/include/clocksource/hyperv_timer.h > > > > +++ b/include/clocksource/hyperv_timer.h > > > > @@ -38,7 +38,7 @@ extern void hv_remap_tsc_clocksource(voi > > > > extern unsigned long hv_get_tsc_pfn(void); > > > > extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void); > > > > > > > > -static inline notrace u64 > > > > +static __always_inline notrace u64 > > > > hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg, u64 = *cur_tsc) > > > > { > > > > u64 scale, offset; > > > > @@ -85,7 +85,7 @@ hv_read_tsc_page_tsc(const struct ms_hyp > > > > return mul_u64_u64_shr(*cur_tsc, scale, 64) + offset; > > > > } > > > > > > > > -static inline notrace u64 > > > > +static __always_inline notrace u64 > > > > hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg) > > > > { > > > > u64 cur_tsc; > > > > > > Hyper-V folks! > > > > > > While reviewing all this I found the following 'gem': > > > > > > hv_init_clocksource() > > > hv_setup_sched_clock() > > > paravirt_set_sched_clock(read_hv_sched_clock_msr) > > > > > > read_hv_sched_clock_msr() [notrace] > > > read_hv_clock_msr() [notrace] > > > hv_get_register() *traced* > > > hv_get_non_nested_register() ... > > > hv_ghcb_msr_read() > > > WARN_ON(in_nmi()) > > > ... > > > local_irq_save() > > > > > > > > > Note that: > > > > > > a) sched_clock() is used in NMI context a *LOT* > > > b) sched_clock() is notrace (or even noinstr with these patches) > > > and local_irq_save() implies tracing > > > > > > > Tianyu and Michael, what's your thought on this? > > > > Is the MSR-based GHCB usable at this point? > > > > What other clock source can be used? >=20 > You do have TSC support -- which is what I fixed for you. It's just the > whole MSR thing that is comically broken. >=20 > You could do a read_hv_clock_msr() implementation using > __rdmsr() and add some sanity checking that anything GHCB using (SEV?) > *will* use TSC. >=20 > Anyway, will you guys do that, or should I pull out the chainsaw and fix > it for you? Peter -- I'll work on a fix. But it will be the first half of next week be= fore I can do it. Michael