On 2/10/2025 4:12 AM, dongli.zhang@xxxxxxxxxx wrote: > Hi Dapeng, > > On 2/7/25 1:52 AM, Mi, Dapeng wrote: >> 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://urldefense.com/v3/__https://lore.kernel.org/all/Zz4uhmuPcZl9vJVr@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!JQx8CdjEI-J6WbzbvB7vHcZ0nJPkzUhvl6TvWvDorAal1XAC17dwpRa6b6Xlva--pK-4ej3Ota0k9SJl3BUWXKTew70$ ). 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://urldefense.com/v3/__https://lore.kernel.org/all/20221119122901.2469-2-dongli.zhang@xxxxxxxxxx/__;!!ACWV5N9M2RV99hQ!JQx8CdjEI-J6WbzbvB7vHcZ0nJPkzUhvl6TvWvDorAal1XAC17dwpRa6b6Xlva--pK-4ej3Ota0k9SJl3BUWzQmZ_yA$ ) >> and post with other our mediated vPMU related patches to enable mediated vPMU? >> >> Thanks! >> >> Dapeng Mi > > Sorry for the delay — it took some effort to learn about mediated vPMU (as > you suggested) to adapt this patch accordingly. > > Yes, feel free to pick up this patch for mediated vPMU, as I don’t want to > block your work, although, I do plan to continue updating it. > > I am continuing working on it, but my primary objective is to reset the AMD > PMU during QEMU reset, which depends on KVM_PMU_CAP_DISABLE. > > [PATCH 5/7] target/i386/kvm: Reset AMD PMU registers during VM reset > [PATCH 6/7] target/i386/kvm: Support perfmon-v2 for reset > > Would you mind keeping me updated on any changes/discussions you make to > QEMU on KVM_PMU_CAP_DISABLE for mediated vPMU? That way, I can adjust my > code accordingly once your QEMU patch for KVM_PMU_CAP_DISABLE is finalized. > > In the meantime, I am continuing working on the entire patchset and I can > change the code when you post the relevant QEMU changes on > KVM_PMU_CAP_DISABLE soon. > > Would that work for you? Dongli, Thanks for your feedback. Sure, I would add you into the mail loop when sending the qemu mediated vPMU patches. BTW, I found Xiaoyao ever sent a quite familiar patch (https://lore.kernel.org/qemu-devel/20220317135913.2166202-10-xiaoyao.li@xxxxxxxxx/) and he has updated the patch to latest qemu code base, I would pick up his patch directly. Thanks, Dapeng Mi > > Thank you very much! > > Dongli Zhang
