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bh=2yRXFDjVp2sxkRLfOrlEnm2BJRPCNwZtlETB+IAjsRY=; b=bYEWeGtnAZzcEd7UZkX81SfeK6hp3cDdyLYvbtNx496uJ8B0srSH5Genfx0BQ83b5ABfUe 0JRso3cnfnP/pEAAH6cG1rgJMPP+cm+NLzhGpKhvqOrw3G8cjbw1QEgSngWpM0X1lPqS8l 64PQ68nEmSIoAyeH9xZaTdJlMyUvoJg= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-323-2Q_4xEL7OYaQjBHyJp2TTA-1; Fri, 19 Mar 2021 12:57:54 -0400 X-MC-Unique: 2Q_4xEL7OYaQjBHyJp2TTA-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5C41587A83B; Fri, 19 Mar 2021 16:57:53 +0000 (UTC) Received: from fuller.cnet (ovpn-112-4.gru2.redhat.com [10.97.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CE9F25C1D1; Fri, 19 Mar 2021 16:57:52 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 2B47A40E4C2A; Fri, 19 Mar 2021 09:37:07 -0300 (-03) Date: Fri, 19 Mar 2021 09:37:07 -0300 From: Marcelo Tosatti To: Chenyi Qiang Subject: Re: [RFC PATCH] i386: Add ratelimit for bus locks acquired in guest Message-ID: <20210319123707.GA72513@fuller.cnet> References: <20210317084709.15605-1-chenyi.qiang@intel.com> <20210318173200.GA35410@fuller.cnet> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mtosatti@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mtosatti@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -14 X-Spam_score: -1.5 X-Spam_bar: - X-Spam_report: (-1.5 / 5.0 requ) BAYES_00=-1.9, DATE_IN_PAST_03_06=1.592, DKIMWL_WL_HIGH=-0.251, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Paolo Bonzini , Richard Henderson , Eduardo Habkost , Xiaoyao Li Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Mar 19, 2021 at 10:59:20AM +0800, Chenyi Qiang wrote: > Hi Marcelo, > > Thank you for your comment. > > On 3/19/2021 1:32 AM, Marcelo Tosatti wrote: > > On Wed, Mar 17, 2021 at 04:47:09PM +0800, Chenyi Qiang wrote: > > > Virtual Machines can exploit bus locks to degrade the performance of > > > system. To address this kind of performance DOS attack, bus lock VM exit > > > is introduced in KVM and it will report the bus locks detected in guest, > > > which can help userspace to enforce throttling policies. > > > > > > > > The availability of bus lock VM exit can be detected through the > > > KVM_CAP_X86_BUS_LOCK_EXIT. The returned bitmap contains the potential > > > policies supported by KVM. The field KVM_BUS_LOCK_DETECTION_EXIT in > > > bitmap is the only supported strategy at present. It indicates that KVM > > > will exit to userspace to handle the bus locks. > > > > > > This patch adds a ratelimit on the bus locks acquired in guest as a > > > mitigation policy. > > > > > > Introduce a new field "bld" to record the limited speed of bus locks in > > > target VM. The user can specify it through the "bus-lock-detection" > > > as a machine property. In current implementation, the default value of > > > the speed is 0 per second, which means no restriction on the bus locks. > > > > > > Ratelimit enforced in data transmission uses a time slice of 100ms to > > > get smooth output during regular operations in block jobs. As for > > > ratelimit on bus lock detection, simply set the ratelimit interval to 1s > > > and restrict the quota of bus lock occurrence to the value of "bld". A > > > potential alternative is to introduce the time slice as a property > > > which can help the user achieve more precise control. > > > > > > The detail of Bus lock VM exit can be found in spec: > > > https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html > > > > > > Signed-off-by: Chenyi Qiang > > > --- > > > hw/i386/x86.c | 6 ++++++ > > > include/hw/i386/x86.h | 7 +++++++ > > > target/i386/kvm/kvm.c | 44 +++++++++++++++++++++++++++++++++++++++++++ > > > 3 files changed, 57 insertions(+) > > > > > > diff --git a/hw/i386/x86.c b/hw/i386/x86.c > > > index 7865660e2c..a70a259e97 100644 > > > --- a/hw/i386/x86.c > > > +++ b/hw/i386/x86.c > > > @@ -1209,6 +1209,12 @@ static void x86_machine_initfn(Object *obj) > > > x86ms->acpi = ON_OFF_AUTO_AUTO; > > > x86ms->smp_dies = 1; > > > x86ms->pci_irq_mask = ACPI_BUILD_PCI_IRQS; > > > + x86ms->bld = 0; > > > + > > > + object_property_add_uint64_ptr(obj, "bus-lock-detection", > > > + &x86ms->bld, OBJ_PROP_FLAG_READWRITE); > > > + object_property_set_description(obj, "bus-lock-detection", > > > + "Bus lock detection ratelimit"); > > > } > > > static void x86_machine_class_init(ObjectClass *oc, void *data) > > > diff --git a/include/hw/i386/x86.h b/include/hw/i386/x86.h > > > index 56080bd1fb..1f0ffbcfb9 100644 > > > --- a/include/hw/i386/x86.h > > > +++ b/include/hw/i386/x86.h > > > @@ -72,6 +72,13 @@ struct X86MachineState { > > > * will be translated to MSI messages in the address space. > > > */ > > > AddressSpace *ioapic_as; > > > + > > > + /* > > > + * ratelimit enforced on detected bus locks, the default value > > > + * is 0 per second > > > + */ > > > + uint64_t bld; > > > + RateLimit bld_limit; > > > }; > > > #define X86_MACHINE_SMM "smm" > > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > > > index c8d61daf68..724862137d 100644 > > > --- a/target/i386/kvm/kvm.c > > > +++ b/target/i386/kvm/kvm.c > > > @@ -130,6 +130,8 @@ static bool has_msr_mcg_ext_ctl; > > > static struct kvm_cpuid2 *cpuid_cache; > > > static struct kvm_msr_list *kvm_feature_msrs; > > > +#define SLICE_TIME 1000000000ULL /* ns */ > > > + > > > int kvm_has_pit_state2(void) > > > { > > > return has_pit_state2; > > > @@ -2267,6 +2269,27 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > > > } > > > } > > > + if (object_dynamic_cast(OBJECT(ms), TYPE_X86_MACHINE)) { > > > + X86MachineState *x86ms = X86_MACHINE(ms); > > > + > > > + if (x86ms->bld > 0) { > > > + ret = kvm_check_extension(s, KVM_CAP_X86_BUS_LOCK_EXIT); > > > + if (!(ret & KVM_BUS_LOCK_DETECTION_EXIT)) { > > > + error_report("kvm: bus lock detection unsupported"); > > > + return -ENOTSUP; > > > + } > > > + ret = kvm_vm_enable_cap(s, KVM_CAP_X86_BUS_LOCK_EXIT, 0, > > > + KVM_BUS_LOCK_DETECTION_EXIT); > > > + if (ret < 0) { > > > + error_report("kvm: Failed to enable bus lock detection cap: %s", > > > + strerror(-ret)); > > > + return ret; > > > + } > > > + > > > + ratelimit_set_speed(&x86ms->bld_limit, x86ms->bld, SLICE_TIME); > > > + } > > > + } > > > + > > > return 0; > > > } > > > @@ -4221,6 +4244,18 @@ void kvm_arch_pre_run(CPUState *cpu, struct kvm_run *run) > > > } > > > } > > > +static void kvm_rate_limit_on_bus_lock(void) > > > +{ > > > + MachineState *ms = MACHINE(qdev_get_machine()); > > > + X86MachineState *x86ms = X86_MACHINE(ms); > > > + > > > + uint64_t delay_ns = ratelimit_calculate_delay(&x86ms->bld_limit, 1); > > > + > > > + if (delay_ns) { > > > + g_usleep(delay_ns / SCALE_US); > > > + } > > > +} > > > > Hi, > > > > Can't see a use-case where the throttling is very useful: this will > > slowdown the application to a halt (if its bus-lock instruction is > > being called frequently). > > > > The throttling is aimed to only slowdown the target application and avoid > slowdown the whole system (if bus-lock is frequent). Right. > As you known, bus locks > takes more cycles and disrupt performance on other cores. Right, testcase shows its pretty bad (cyclictest latency goes from 5us to > 200us). > > > However its very nice to know that it (bus lock) has happened. > > > > So on KVM bus exit do you emulate the instruction or just execute it > > in the guest (without a VM-exit for the second time) ? > > > Bus lock VM exit is a trap-like VM exit and delivered following the > execution of the instruction acquiring the bus lock. Thus, it can just > detect the occurrence of bus locks and can't intercept it. In KVM, we don't > emulate the instruction. Bus lock already happens and guest will proceed to > execute. I see. Question: its possible to #AC trap the split-lock in a KVM guest, right? https://lwn.net/Articles/810317/