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Tue, 8 Jun 2021 04:24:41 -0400 (EDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.de; i=@amazon.de; q=dns/txt; s=amazon201209; t=1623140682; x=1654676682; h=from:to:cc:date:message-id:references:in-reply-to: content-id:mime-version:content-transfer-encoding:subject; bh=0Y5gzEbn1hAeMJTVGWpCtXqdBYiMxoJcWc7kGY52UDw=; b=ROWT5sIt6/1qKWCslUl6K/Pk1WTUpAGfZx8iYsD97eIxHpVjDVBiNjiy YaWAOJL6Vw7BmjiSFt1NyQGR41ydPNeMYn+JN6uVOAd4Ar3OH+h9ZsaUy dR+mbiZcIdljsp4VpL9sf3yFScV3PqH9hrnBXsuAMBbOTzFFfzM7eX7D3 0=; X-IronPort-AV: E=Sophos;i="5.83,257,1616457600"; d="scan'208";a="118713622" Subject: Re: [PATCH] KVM: arm64: Properly restore PMU state during live-migration Thread-Topic: [PATCH] KVM: arm64: Properly restore PMU state during live-migration Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-1d-2c665b5d.us-east-1.amazon.com) ([10.43.8.6]) by smtp-border-fw-6001.iad6.amazon.com with ESMTP; 08 Jun 2021 08:24:35 +0000 Received: from EX13MTAUWA001.ant.amazon.com (iad55-ws-svc-p15-lb9-vlan2.iad.amazon.com [10.40.159.162]) by email-inbound-relay-1d-2c665b5d.us-east-1.amazon.com (Postfix) with ESMTPS id 1604AA1F18; Tue, 8 Jun 2021 08:24:31 +0000 (UTC) Received: from EX13D20UWA003.ant.amazon.com (10.43.160.97) by EX13MTAUWA001.ant.amazon.com (10.43.160.58) with Microsoft SMTP Server (TLS) id 15.0.1497.18; Tue, 8 Jun 2021 08:24:31 +0000 Received: from EX13D19EUA001.ant.amazon.com (10.43.165.74) by EX13D20UWA003.ant.amazon.com (10.43.160.97) with Microsoft SMTP Server (TLS) id 15.0.1497.18; Tue, 8 Jun 2021 08:24:30 +0000 Received: from EX13D19EUA001.ant.amazon.com ([10.43.165.74]) by EX13D19EUA001.ant.amazon.com ([10.43.165.74]) with mapi id 15.00.1497.018; Tue, 8 Jun 2021 08:24:29 +0000 From: "Jain, Jinank" To: "maz@kernel.org" Thread-Index: AQHXWGiDwgcuw84aU0uAgEUSGDYWHasCc0sAgAZJnQCAAAh2gIAAITgAgADmZgCAAAGZgA== Date: Tue, 8 Jun 2021 08:24:29 +0000 Message-ID: References: <20210603110554.13643-1-jinankj@amazon.de> <87wnrbylxv.wl-maz@kernel.org> <0a694ea93303bfa04530cd940f692244e1ccd1e7.camel@amazon.de> <87lf7lzl8c.wl-maz@kernel.org> <87eedczs49.wl-maz@kernel.org> In-Reply-To: <87eedczs49.wl-maz@kernel.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.43.165.82] Content-ID: <52137560E1E4624F94DAC99ABDCDDB3A@amazon.com> MIME-Version: 1.0 X-Mailman-Approved-At: Tue, 08 Jun 2021 09:05:46 -0400 Cc: "Graf \(AWS\), Alexander" , "will@kernel.org" , "linux-kernel@vger.kernel.org" , "catalin.marinas@arm.com" , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, 2021-06-08 at 09:18 +0100, Marc Zyngier wrote: > CAUTION: This email originated from outside of the organization. Do > not click links or open attachments unless you can confirm the sender > and know the content is safe. > > > > On Mon, 07 Jun 2021 19:34:08 +0100, > "Jain, Jinank" wrote: > > Hi Marc. > > > > On Mon, 2021-06-07 at 17:35 +0100, Marc Zyngier wrote: > > > CAUTION: This email originated from outside of the organization. > > > Do > > > not click links or open attachments unless you can confirm the > > > sender > > > and know the content is safe. > > > > > > > > > > > > On Mon, 07 Jun 2021 17:05:01 +0100, > > > "Jain, Jinank" wrote: > > > > On Thu, 2021-06-03 at 17:03 +0100, Marc Zyngier wrote: > > > > > Hi Jinank, > > > > > > > > > > On Thu, 03 Jun 2021 12:05:54 +0100, > > > > > Jinank Jain wrote: > > > > > > Currently if a guest is live-migrated while it is actively > > > > > > using > > > > > > perf > > > > > > counters, then after live-migrate it will notice that all > > > > > > counters > > > > > > would > > > > > > suddenly start reporting 0s. This is due to the fact we are > > > > > > not > > > > > > re-creating the relevant perf events inside the kernel. > > > > > > > > > > > > Usually on live-migration guest state is restored using > > > > > > KVM_SET_ONE_REG > > > > > > ioctl interface, which simply restores the value of PMU > > > > > > registers > > > > > > values but does not re-program the perf events so that the > > > > > > guest > > > > > > can seamlessly > > > > > > use these counters even after live-migration like it was > > > > > > doing > > > > > > before > > > > > > live-migration. > > > > > > > > > > > > Instead there are two completely different code path > > > > > > between > > > > > > guest > > > > > > accessing PMU registers and VMM restoring counters on > > > > > > live-migration. > > > > > > > > > > > > In case of KVM_SET_ONE_REG: > > > > > > > > > > > > kvm_arm_set_reg() > > > > > > ...... kvm_arm_sys_reg_set_reg() > > > > > > ........... reg_from_user() > > > > > > > > > > > > but in case when guest tries to access these counters: > > > > > > > > > > > > handle_exit() > > > > > > ..... kvm_handle_sys_reg() > > > > > > ..........perform_access() > > > > > > ...............access_pmu_evcntr() > > > > > > ...................kvm_pmu_set_counter_value() > > > > > > .......................kvm_pmu_create_perf_event() > > > > > > > > > > > > The drawback of using the KVM_SET_ONE_REG interface is that > > > > > > the > > > > > > host pmu > > > > > > events which were registered for the source instance and > > > > > > not > > > > > > present for > > > > > > the destination instance. > > > > > > > > > > I can't parse this sentence. Do you mean "are not present"? > > > > > > > > > > > Thus passively restoring PMCR_EL0 using > > > > > > KVM_SET_ONE_REG interface would not create the necessary > > > > > > host > > > > > > pmu > > > > > > events > > > > > > which are crucial for seamless guest experience across live > > > > > > migration. > > > > > > > > > > > > In ordet to fix the situation, on first vcpu load we should > > > > > > restore > > > > > > PMCR_EL0 in the same exact way like the guest was trying to > > > > > > access > > > > > > these counters. And then we will also recreate the relevant > > > > > > host > > > > > > pmu > > > > > > events. > > > > > > > > > > > > Signed-off-by: Jinank Jain > > > > > > Cc: Alexander Graf (AWS) > > > > > > Cc: Marc Zyngier > > > > > > Cc: James Morse > > > > > > Cc: Alexandru Elisei > > > > > > Cc: Suzuki K Poulose > > > > > > Cc: Catalin Marinas > > > > > > Cc: Will Deacon > > > > > > --- > > > > > > arch/arm64/include/asm/kvm_host.h | 1 + > > > > > > arch/arm64/kvm/arm.c | 1 + > > > > > > arch/arm64/kvm/pmu-emul.c | 10 ++++++++-- > > > > > > arch/arm64/kvm/pmu.c | 15 +++++++++++++++ > > > > > > include/kvm/arm_pmu.h | 3 +++ > > > > > > 5 files changed, 28 insertions(+), 2 deletions(-) > > > > > > > > > > > > diff --git a/arch/arm64/include/asm/kvm_host.h > > > > > > b/arch/arm64/include/asm/kvm_host.h > > > > > > index 7cd7d5c8c4bc..2376ad3c2fc2 100644 > > > > > > --- a/arch/arm64/include/asm/kvm_host.h > > > > > > +++ b/arch/arm64/include/asm/kvm_host.h > > > > > > @@ -745,6 +745,7 @@ static inline int > > > > > > kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu) > > > > > > void kvm_set_pmu_events(u32 set, struct perf_event_attr > > > > > > *attr); > > > > > > void kvm_clr_pmu_events(u32 clr); > > > > > > > > > > > > +void kvm_vcpu_pmu_restore(struct kvm_vcpu *vcpu); > > > > > > void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu); > > > > > > void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu); > > > > > > #else > > > > > > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > > > > > > index e720148232a0..c66f6d16ec06 100644 > > > > > > --- a/arch/arm64/kvm/arm.c > > > > > > +++ b/arch/arm64/kvm/arm.c > > > > > > @@ -408,6 +408,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu > > > > > > *vcpu, > > > > > > int cpu) > > > > > > if (has_vhe()) > > > > > > kvm_vcpu_load_sysregs_vhe(vcpu); > > > > > > kvm_arch_vcpu_load_fp(vcpu); > > > > > > + kvm_vcpu_pmu_restore(vcpu); > > > > > > > > > > If this only needs to be run once per vcpu, why not trigger > > > > > it > > > > > from > > > > > kvm_arm_pmu_v3_enable(), which is also called once per vcpu? > > > > > > > > > > This can done on the back of a request, saving most of the > > > > > overhead > > > > > and not requiring any extra field. Essentially, something > > > > > like > > > > > the > > > > > (untested) patch below. > > > > > > > > > > > kvm_vcpu_pmu_restore_guest(vcpu); > > > > > > if (kvm_arm_is_pvtime_enabled(&vcpu->arch)) > > > > > > kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu); > > > > > > diff --git a/arch/arm64/kvm/pmu-emul.c > > > > > > b/arch/arm64/kvm/pmu- > > > > > > emul.c > > > > > > index fd167d4f4215..12a40f4b5f0d 100644 > > > > > > --- a/arch/arm64/kvm/pmu-emul.c > > > > > > +++ b/arch/arm64/kvm/pmu-emul.c > > > > > > @@ -574,10 +574,16 @@ void kvm_pmu_handle_pmcr(struct > > > > > > kvm_vcpu > > > > > > *vcpu, u64 val) > > > > > > kvm_pmu_disable_counter_mask(vcpu, mask); > > > > > > } > > > > > > > > > > > > - if (val & ARMV8_PMU_PMCR_C) > > > > > > + /* > > > > > > + * Cycle counter needs to reset in case of first vcpu > > > > > > load. > > > > > > + */ > > > > > > + if (val & ARMV8_PMU_PMCR_C || > > > > > > !kvm_arm_pmu_v3_restored(vcpu)) > > > > > > > > > > Why? There is no architectural guarantee that a counter > > > > > resets to > > > > > 0 > > > > > without writing PMCR_EL0.C. And if you want the guest to > > > > > continue > > > > > counting where it left off, resetting the counter is at best > > > > > counter-productive. > > > > > > > > Without this we would not be resetting PMU which is required > > > > for > > > > creating host perf events. With the patch that you suggested we > > > > are > > > > restoring PMCR_EL0 properly but still missing recreation of > > > > host > > > > perf > > > > events. > > > > > > How? The request that gets set on the first vcpu run will call > > > kvm_pmu_handle_pmcr() -> kvm_pmu_enable_counter_mask() -> > > > kvm_pmu_create_perf_event(). What are we missing? > > > > > > > I found out what I was missing. I was working with an older kernel > > which was missing this upstream patch: > > > > https://lore.kernel.org/lkml/20200124142535.29386-3-eric.auger@redhat.com/ > > :-( > > Please test whatever you send with an upstream kernel. Actually, > please *develop* on an upstream kernel. This will avoid this kind of > discussion where we talk past each other, and make it plain that your > production kernel is lacking all sorts of fixes. > > Now, can you please state whether or not this patch fixes it for you > *on an upstream kernel*? I have no interest in results from a > production kernel. > > M. > Really sorry for the noise and I can confirm that your suggested patch fixes the problem for the upstream kernel i.e., if I live migrate a guest which is actively using perf events then the guest can continue using them even after live migration without interruption. > -- > Without deviation from the norm, progress is not possible. Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm