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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 50497C433F5 for ; Wed, 8 Dec 2021 12:44:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=E7sEzQKeq0yOolrOZzdC7KBAXy4QX1LrwjM8Mw5lsV8=; b=Vx52D+D9UmS4MP dJ5OTjr92N7FmMB26LjRQ7PWgQx5pYU7IdT2wsuXohjp0na4Aj23uYFw/aK2RkL5ayC4AZm8ifQfQ QATpewmj0pcO3ZEmtTcsv6FWZVc9vnP4QVVmPvYPsTI51VsxyS3MGsLeibmS3XjjuOpyPLK8gEgA7 9YcePxws4PkkZIcpKYToGiTStuV28/gf/biKJLDJQizINJ2jBX+8oGRHedzJakxaERp6byazlWUWY Z0D5H68UO29/Q1IS15H8HHxuALiDhyC8xvvaAM1xjREXRr/vAql4zpyfwcFnOr/zD6Ysw/SN+ij/C BUv1+bd7k0IJRJKhP/xA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1muwI6-00CXsd-Kc; Wed, 08 Dec 2021 12:43:23 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1muwI2-00CXqw-BK for linux-arm-kernel@lists.infradead.org; Wed, 08 Dec 2021 12:43:20 +0000 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 81ED81042; Wed, 8 Dec 2021 04:43:16 -0800 (PST) Received: from monolith.localdoman (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C8DF23F73B; Wed, 8 Dec 2021 04:43:14 -0800 (PST) Date: Wed, 8 Dec 2021 12:43:13 +0000 From: Alexandru Elisei To: Reiji Watanabe Cc: maz@kernel.org, mingo@redhat.com, tglx@linutronix.de, will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 3/4] KVM: arm64: Add KVM_ARM_VCPU_PMU_V3_SET_PMU attribute Message-ID: References: <20211206170223.309789-1-alexandru.elisei@arm.com> <20211206170223.309789-4-alexandru.elisei@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211208_044318_525337_B2A7A837 X-CRM114-Status: GOOD ( 55.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On Wed, Dec 08, 2021 at 12:23:44PM +0000, Alexandru Elisei wrote: > Hi Reiji, > > On Tue, Dec 07, 2021 at 07:13:17PM -0800, Reiji Watanabe wrote: > > Hi Alex, > > > > On Mon, Dec 6, 2021 at 9:02 AM 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 | 37 +++++++++++++++++++++++-- > > > include/kvm/arm_pmu.h | 1 + > > > tools/arch/arm64/include/uapi/asm/kvm.h | 1 + > > > 5 files changed, 63 insertions(+), 2 deletions(-) > > > > > > diff --git a/Documentation/virt/kvm/devices/vcpu.rst b/Documentation/virt/kvm/devices/vcpu.rst > > > index 60a29972d3f1..c82be5cbc268 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 > > > + -ENXIO PMU not found > > > + -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 CPU PMUs on the system. > > > + > > > +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 eaaad4c06561..618138c5f792 100644 > > > --- a/arch/arm64/kvm/pmu-emul.c > > > +++ b/arch/arm64/kvm/pmu-emul.c > > > @@ -603,6 +603,7 @@ 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; > > > @@ -638,8 +639,7 @@ 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 +941,29 @@ 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; > > > + int ret = -ENXIO; > > > + > > > + mutex_lock(&arm_pmus_lock); > > > + > > > + 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; > > > > Shouldn't kvm->arch.pmuver be updated based on the pmu that > > is used for the guest ? > > As far as I can tell, kvm->arch.pmuver is used in kvm_pmu_event_mask() to > get the number of available perf events, which is then used for configuring > events (via the PMEVTYPER_EL0) register or for masking out events when the > guest reads PMCEID{0,1}_EL0; the events that are masked out are the events > that are unsupported by the PMU that perf will choose for creating events. > > This series doesn't forbid userspace from setting the PMU for only a subset > of VCPUs, leaving the other VCPUs with the default PMU, so setting > kvm->arch.pmuver to a particular VCPU's PMU is not correct. > > I think the correct fix here would be to have kvm_pmu_event_mask() use the > VCPU's PMU PMUVer, and fallback to kvm->arch.pmuver if that isn't set. > > This makes me wonder. Should KVM enforce having userspace either not > setting the PMU for any VCPU, either setting it for all VCPUs? I think this > would be a good idea and will reduce complexity in the long run. I also > don't see a use case for userspace choosing to set the PMU for a subset of > VCPUs, leaving the other VCPUs with the default behaviour. I had a look and I don't think there's a way to enforce this, as there are no restrictions on when a VCPU can be created. KVM must support only a subset of VCPUs having a PMU set. Thanks, Alex > > Thanks, > Alex > > > > > Thanks, > > Reiji > > > > > > > + ret = 0; > > > + goto out_unlock; > > > + } > > > + } > > > + > > > +out_unlock: > > > + mutex_unlock(&arm_pmus_lock); > > > + return ret; > > > +} > > > + > > > int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) > > > { > > > if (!kvm_vcpu_has_pmu(vcpu)) > > > @@ -1027,6 +1050,15 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) > > > > > > return 0; > > > } > > > + case KVM_ARM_VCPU_PMU_V3_SET_PMU: { > > > + int __user *uaddr = (int __user *)(long)attr->addr; > > > + int pmu_id; > > > + > > > + if (get_user(pmu_id, uaddr)) > > > + return -EFAULT; > > > + > > > + return kvm_arm_pmu_v3_set_pmu(vcpu, pmu_id); > > > + } > > > case KVM_ARM_VCPU_PMU_V3_INIT: > > > return kvm_arm_pmu_v3_init(vcpu); > > > } > > > @@ -1064,6 +1096,7 @@ int kvm_arm_pmu_v3_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr) > > > case KVM_ARM_VCPU_PMU_V3_IRQ: > > > case KVM_ARM_VCPU_PMU_V3_INIT: > > > case KVM_ARM_VCPU_PMU_V3_FILTER: > > > + case KVM_ARM_VCPU_PMU_V3_SET_PMU: > > > if (kvm_vcpu_has_pmu(vcpu)) > > > return 0; > > > } > > > diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h > > > index e249c5f172aa..ab3046a8f9bb 100644 > > > --- a/include/kvm/arm_pmu.h > > > +++ b/include/kvm/arm_pmu.h > > > @@ -34,6 +34,7 @@ struct kvm_pmu { > > > bool created; > > > bool irq_level; > > > struct irq_work overflow_work; > > > + struct arm_pmu *arm_pmu; > > > }; > > > > > > struct arm_pmu_entry { > > > diff --git a/tools/arch/arm64/include/uapi/asm/kvm.h b/tools/arch/arm64/include/uapi/asm/kvm.h > > > index b3edde68bc3e..1d0a0a2a9711 100644 > > > --- a/tools/arch/arm64/include/uapi/asm/kvm.h > > > +++ b/tools/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 > > > -- > > > 2.34.1 > > > > > > _______________________________________________ > > > kvmarm mailing list > > > kvmarm@lists.cs.columbia.edu > > > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm > _______________________________________________ > kvmarm mailing list > kvmarm@lists.cs.columbia.edu > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel