On 11/21/2024 6:06 PM, Mi, Dapeng wrote: > On 11/8/2024 7:44 AM, dongli.zhang@xxxxxxxxxx wrote: >> Hi Zhao, >> >> >> On 11/6/24 11:52 PM, Zhao Liu wrote: >>> (+Dapang & Zide) >>> >>> Hi Dongli, >>> >>> On Mon, Nov 04, 2024 at 01:40:17AM -0800, Dongli Zhang wrote: >>>> Date: Mon, 4 Nov 2024 01:40:17 -0800 >>>> From: Dongli Zhang <dongli.zhang@xxxxxxxxxx> >>>> Subject: [PATCH 2/7] target/i386/kvm: introduce 'pmu-cap-disabled' to set >>>> KVM_PMU_CAP_DISABLE >>>> X-Mailer: git-send-email 2.43.5 >>>> >>>> The AMD PMU virtualization is not disabled when configuring >>>> "-cpu host,-pmu" in the QEMU command line on an AMD server. Neither >>>> "-cpu host,-pmu" nor "-cpu EPYC" effectively disables AMD PMU >>>> virtualization in such an environment. >>>> >>>> As a result, VM logs typically show: >>>> >>>> [ 0.510611] Performance Events: Fam17h+ core perfctr, AMD PMU driver. >>>> >>>> whereas the expected logs should be: >>>> >>>> [ 0.596381] Performance Events: PMU not available due to virtualization, using software events only. >>>> [ 0.600972] NMI watchdog: Perf NMI watchdog permanently disabled >>>> >>>> This discrepancy occurs because AMD PMU does not use CPUID to determine >>>> whether PMU virtualization is supported. >>> Intel platform doesn't have this issue since Linux kernel fails to check >>> the CPU family & model when "-cpu *,-pmu" option clears PMU version. >>> >>> The difference between Intel and AMD platforms, however, is that it seems >>> Intel hardly ever reaches the “...due virtualization” message, but >>> instead reports an error because it recognizes a mismatched family/model. >>> >>> This may be a drawback of the PMU driver's print message, but the result >>> is the same, it prevents the PMU driver from enabling. >>> >>> So, please mention that KVM_PMU_CAP_DISABLE doesn't change the PMU >>> behavior on Intel platform because current "pmu" property works as >>> expected. >> Sure. I will mention this in v2. >> >>>> To address this, we introduce a new property, 'pmu-cap-disabled', for KVM >>>> acceleration. This property sets KVM_PMU_CAP_DISABLE if >>>> KVM_CAP_PMU_CAPABILITY is supported. Note that this feature currently >>>> supports only x86 hosts, as KVM_CAP_PMU_CAPABILITY is used exclusively for >>>> x86 systems. >>>> >>>> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx> >>>> --- >>>> Another previous solution to re-use '-cpu host,-pmu': >>>> https://urldefense.com/v3/__https://lore.kernel.org/all/20221119122901.2469-1-dongli.zhang@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!Nm8Db-mwBoMIwKkRqzC9kgNi5uZ7SCIf43zUBn92Ar_NEbLXq-ZkrDDvpvDQ4cnS2i4VyKAp6CRVE12bRkMF$ >>> IMO, I prefer the previous version. This VM-level KVM property is >>> difficult to integrate with the existing CPU properties. Pls refer later >>> comments for reasons. >>> >>>> accel/kvm/kvm-all.c | 1 + >>>> include/sysemu/kvm_int.h | 1 + >>>> qemu-options.hx | 9 ++++++- >>>> target/i386/cpu.c | 2 +- >>>> target/i386/kvm/kvm.c | 52 ++++++++++++++++++++++++++++++++++++++ >>>> target/i386/kvm/kvm_i386.h | 2 ++ >>>> 6 files changed, 65 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c >>>> index 801cff16a5..8b5ba45cf7 100644 >>>> --- a/accel/kvm/kvm-all.c >>>> +++ b/accel/kvm/kvm-all.c >>>> @@ -3933,6 +3933,7 @@ static void kvm_accel_instance_init(Object *obj) >>>> s->xen_evtchn_max_pirq = 256; >>>> s->device = NULL; >>>> s->msr_energy.enable = false; >>>> + s->pmu_cap_disabled = false; >>>> } >>> The CPU property "pmu" also defaults to "false"...but: >>> >>> * max CPU would override this and try to enable PMU by default in >>> max_x86_cpu_initfn(). >>> >>> * Other named CPU models keep the default setting to avoid affecting >>> the migration. >>> >>> The pmu_cap_disabled and “pmu” property look unbound and unassociated, >>> so this can cause the conflict when they are not synchronized. For >>> example, >>> >>> -cpu host -accel kvm,pmu-cap-disabled=on >>> >>> The above options will fail to launch a VM (on Intel platform). >>> >>> Ideally, the “pmu” property and pmu-cap-disabled should be bound to each >>> other and be consistent. But it's not easy because: >>> - There is no proper way to have pmu_cap_disabled set different default >>> values (e.g., "false" for max CPU and "true" for named CPU models) >>> based on different CPU models. >>> - And, no proper place to check the consistency of pmu_cap_disabled and >>> enable_pmu. >>> >>> Therefore, I prefer your previous approach, to reuse current CPU "pmu" >>> property. >> Thank you very much for the suggestion and reasons. >> >> I am going to follow your suggestion to switch back to the previous solution in v2. > +1. > > I also prefer to leverage current exist "+/-pmu" option instead of adding > a new option. More options, more complexity. When they are not > inconsistent, which has higher priority? all these are issues. > > Although KVM_CAP_PMU_CAPABILITY is a VM-level PMU capability, but all CPUs > in a same VM should always share same PMU configuration (Don't consider > hybrid platforms which have many issues need to be handled specifically). > > >>> Further, considering that this is currently the only case that needs to >>> to set the VM level's capability in the CPU context, there is no need to >>> introduce a new kvm interface (in your previous patch), which can instead >>> be set in kvm_cpu_realizefn(), like: >>> >>> >>> diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c >>> index 99d1941cf51c..05e9c9a1a0cf 100644 >>> --- a/target/i386/kvm/kvm-cpu.c >>> +++ b/target/i386/kvm/kvm-cpu.c >>> @@ -42,6 +42,8 @@ static bool kvm_cpu_realizefn(CPUState *cs, Error **errp) >>> { >>> X86CPU *cpu = X86_CPU(cs); >>> CPUX86State *env = &cpu->env; >>> + KVMState *s = kvm_state; >>> + static bool first = true; >>> bool ret; >>> >>> /* >>> @@ -63,6 +65,29 @@ static bool kvm_cpu_realizefn(CPUState *cs, Error **errp) >>> * check/update ucode_rev, phys_bits, guest_phys_bits, mwait >>> * cpu_common_realizefn() (via xcc->parent_realize) >>> */ >>> + >>> + if (first) { >>> + first = false; >>> + >>> + /* >>> + * Since Linux v5.18, KVM provides a VM-level capability to easily >>> + * disable PMUs; however, QEMU has been providing PMU property per >>> + * CPU since v1.6. In order to accommodate both, have to configure >>> + * the VM-level capability here. >>> + */ >>> + if (!cpu->enable_pmu && >>> + kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY)) { >>> + int r = kvm_vm_enable_cap(s, KVM_CAP_PMU_CAPABILITY, 0, >>> + KVM_PMU_CAP_DISABLE); >>> + >>> + if (r < 0) { >>> + error_setg(errp, "kvm: Failed to disable pmu cap: %s", >>> + strerror(-r)); >>> + return false; >>> + } >>> + } > It seems KVM_CAP_PMU_CAPABILITY is called to only disable PMU here. From > point view of logic completeness, KVM_CAP_PMU_CAPABILITY should be called > to enabled PMU as well when user wants to enable PMU. > > I know currently we only need to disable PMU, but we may need to enable PMU > via KVM_CAP_PMU_CAPABILITY soon. > > We are working on the new KVM mediated vPMU framework, Sean suggest to > leverage KVM_CAP_PMU_CAPABILITY to enable mediated vPMU dynamically > (https://lore.kernel.org/all/Zz4uhmuPcZl9vJVr@xxxxxxxxxx/). So It would be > better if the enable logic can be added here as well. > > Thanks. Hi Dongli, May I know if you have plan to continue to update this patch recently? As previous comment said, our KVM mediated vPMU solution needs qemu to explicitly call KVM_CAP_PMU_CAPABILITY to enable mediated vPMU as well. If you have no plan to update this patch recently, would you mind me to pick up this patch (https://lore.kernel.org/all/20221119122901.2469-2-dongli.zhang@xxxxxxxxxx/) and post with other our mediated vPMU related patches to enable mediated vPMU? Thanks! Dapeng Mi > > >>> + } >>> + >>> if (cpu->max_features) { >>> if (enable_cpu_pm) { >>> if (kvm_has_waitpkg()) { >>> --- >> Sure. I will limit the change within only x86 + KVM. >> >>> In addition, if PMU is disabled, why not mask the perf related bits in >>> 8000_0001_ECX? :) >>> >> My fault. I have masked only 0x80000022, and I forgot 0x80000001 for AMD. >> >> Thank you very much for the reminder. >> >> >> I will wait for a day or maybe the weekend. I am going to switch to the previous >> solution in v2 if there isn't any further objection with a more valid reason. >> >> Thank you very much for the feedback! >> >> Dongli Zhang >> >>
