From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CD41C433F5 for ; Mon, 22 Nov 2021 11:27:51 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 78A7E4B1AD; Mon, 22 Nov 2021 06:27:51 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id uyM+U5KYZ625; Mon, 22 Nov 2021 06:27:50 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 0508C4B175; Mon, 22 Nov 2021 06:27:50 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 44FCB4B16C for ; Mon, 22 Nov 2021 06:27:49 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id d85cEn7WL-zY for ; Mon, 22 Nov 2021 06:27:47 -0500 (EST) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 0FD8F4B13A for ; Mon, 22 Nov 2021 06:27:47 -0500 (EST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 751391042; Mon, 22 Nov 2021 03:27:46 -0800 (PST) Received: from monolith.localdoman (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9BCC03F73B; Mon, 22 Nov 2021 03:27:44 -0800 (PST) Date: Mon, 22 Nov 2021 11:29:36 +0000 From: Alexandru Elisei To: Marc Zyngier Subject: Re: [PATCH 3/4] KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute Message-ID: References: <20211115165041.194884-1-alexandru.elisei@arm.com> <20211115165041.194884-4-alexandru.elisei@arm.com> <87czmts4rh.wl-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <87czmts4rh.wl-maz@kernel.org> Cc: will@kernel.org, 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 Hi Marc, Thanks for having a look! On Sun, Nov 21, 2021 at 07:11:30PM +0000, Marc Zyngier wrote: > On Mon, 15 Nov 2021 16:50:40 +0000, > Alexandru Elisei wrote: > > > > When KVM creates an event and there are more than one PMUs present on the > > system, perf_init_event() will go through the list of available PMUs and > > will choose the first one that can create the event. The order of the PMUs > > in the PMU list depends on the probe order, which can change under various > > circumstances, for example if the order of the PMU nodes change in the DTB > > or if asynchronous driver probing is enabled on the kernel command line > > (with the driver_async_probe=armv8-pmu option). > > > > Another consequence of this approach is that, on heteregeneous systems, > > all virtual machines that KVM creates will use the same PMU. This might > > cause unexpected behaviour for userspace: when a VCPU is executing on > > the physical CPU that uses this PMU, PMU events in the guest work > > correctly; but when the same VCPU executes on another CPU, PMU events in > > the guest will suddenly stop counting. > > > > Fortunately, perf core allows user to specify on which PMU to create an > > event by using the perf_event_attr->type field, which is used by > > perf_init_event() as an index in the radix tree of available PMUs. > > > > Add the KVM_ARM_VCPU_PMU_V3_CTRL(KVM_ARM_VCPU_PMU_V3_SET_PMU) VCPU > > attribute to allow userspace to specify the arm_pmu that KVM will use when > > creating events for that VCPU. KVM will make no attempt to run the VCPU on > > the physical CPUs that share this PMU, leaving it up to userspace to > > manage the VCPU threads' affinity accordingly. > > > > Signed-off-by: Alexandru Elisei > > --- > > Documentation/virt/kvm/devices/vcpu.rst | 25 ++++++++++++++++++++ > > arch/arm64/include/uapi/asm/kvm.h | 1 + > > arch/arm64/kvm/pmu-emul.c | 31 +++++++++++++++++++++++-- > > include/kvm/arm_pmu.h | 1 + > > tools/arch/arm64/include/uapi/asm/kvm.h | 1 + > > 5 files changed, 57 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst > > index 60a29972d3f1..59ac382af59a 100644 > > --- a/Documentation/virt/kvm/devices/vcpu.rst > > +++ b/Documentation/virt/kvm/devices/vcpu.rst > > @@ -104,6 +104,31 @@ hardware event. Filtering event 0x1E (CHAIN) has no effect either, as it > > isn't strictly speaking an event. Filtering the cycle counter is possible > > using event 0x11 (CPU_CYCLES). > > > > +1.4 ATTRIBUTE: KVM_ARM_VCPU_PMU_V3_SET_PMU > > +------------------------------------------ > > + > > +:Parameters: in kvm_device_attr.addr the address to an int representing the PMU > > + identifier. > > + > > +:Returns: > > + > > + ======= =============================================== > > + -EBUSY PMUv3 already initialized > > + -EFAULT Error accessing the PMU identifier > > + -EINVAL PMU not found or PMU name longer than PAGE_SIZE > > + -ENODEV PMUv3 not supported or GIC not initialized > > + -ENOMEM Could not allocate memory > > + ======= =============================================== > > + > > +Request that the VCPU uses the specified hardware PMU when creating guest events > > +for the purpose of PMU emulation. The PMU identifier can be read from the "type" > > +file for the desired PMU instance under /sys/devices (or, equivalent, > > +/sys/bus/even_source). This attribute is particularly useful on heterogeneous > > +systems where there are at least two PMUs on the system. > > nit: CPU PMUs. A number of systems have 'uncore' PMUs which KVM > totally ignores. Sure, will change. > > > + > > +Note that KVM will not make any attempts to run the VCPU on the physical CPUs > > +associated with the PMU specified by this attribute. This is entirely left to > > +userspace. > > > > 2. GROUP: KVM_ARM_VCPU_TIMER_CTRL > > ================================= > > diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h > > index b3edde68bc3e..1d0a0a2a9711 100644 > > --- a/arch/arm64/include/uapi/asm/kvm.h > > +++ b/arch/arm64/include/uapi/asm/kvm.h > > @@ -362,6 +362,7 @@ struct kvm_arm_copy_mte_tags { > > #define KVM_ARM_VCPU_PMU_V3_IRQ 0 > > #define KVM_ARM_VCPU_PMU_V3_INIT 1 > > #define KVM_ARM_VCPU_PMU_V3_FILTER 2 > > +#define KVM_ARM_VCPU_PMU_V3_SET_PMU 3 > > #define KVM_ARM_VCPU_TIMER_CTRL 1 > > #define KVM_ARM_VCPU_TIMER_IRQ_VTIMER 0 > > #define KVM_ARM_VCPU_TIMER_IRQ_PTIMER 1 > > diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c > > index dab335d17409..53cedeb5dbf6 100644 > > --- a/arch/arm64/kvm/pmu-emul.c > > +++ b/arch/arm64/kvm/pmu-emul.c > > @@ -602,6 +602,7 @@ static bool kvm_pmu_counter_is_enabled(struct kvm_vcpu *vcpu, u64 select_idx) > > static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx) > > { > > struct kvm_pmu *pmu = &vcpu->arch.pmu; > > + struct arm_pmu *arm_pmu = pmu->arm_pmu; > > struct kvm_pmc *pmc; > > struct perf_event *event; > > struct perf_event_attr attr; > > @@ -637,8 +638,7 @@ static void kvm_pmu_create_perf_event(struct kvm_vcpu *vcpu, u64 select_idx) > > return; > > > > memset(&attr, 0, sizeof(struct perf_event_attr)); > > - attr.type = PERF_TYPE_RAW; > > - attr.size = sizeof(attr); > > + attr.type = arm_pmu ? arm_pmu->pmu.type : PERF_TYPE_RAW; > > attr.pinned = 1; > > attr.disabled = !kvm_pmu_counter_is_enabled(vcpu, pmc->idx); > > attr.exclude_user = data & ARMV8_PMU_EXCLUDE_EL0 ? 1 : 0; > > @@ -941,6 +941,23 @@ static bool pmu_irq_is_valid(struct kvm *kvm, int irq) > > return true; > > } > > > > +static int kvm_arm_pmu_v3_set_pmu(struct kvm_vcpu *vcpu, int pmu_id) > > +{ > > + struct kvm_pmu *kvm_pmu = &vcpu->arch.pmu; > > + struct arm_pmu_entry *entry; > > + struct arm_pmu *arm_pmu; > > + > > + list_for_each_entry(entry, &arm_pmus, entry) { > > + arm_pmu = entry->arm_pmu; > > + if (arm_pmu->pmu.type == pmu_id) { > > + kvm_pmu->arm_pmu = arm_pmu; > > + return 0; > > + } > > + } > > How does this work when a new CPU gets hotplugged on, bringing a new > PMU type along? It doesn't seem safe to parse this list without any > locking. It wouldn't work at all. I missed the fact that hotplogging a CPU means writing to the list of PMUs after the initial driver probing which happens at boot. This needs to be protected against concurrent writes, I will fix it. > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible. _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm