Re: [PATCH v2 0/2] target/i386/kvm: fix two svm pmu virtualization bugs

[Like Xu <like.xu.linux@gmail.com>]

I think we've been stuck here too long. Sorry Dongli.

+zhenyu, could you get someone to follow up on this, or I will start working on 
that.

On 9/1/2023 9:19 am, Dongli Zhang wrote:
> Ping?
> 
> About [PATCH v2 2/2], the bad thing is that the customer will not be able to
> notice the issue, that is, the "Broken BIOS detected" in dmesg, immediately.
> 
> As a result, the customer VM many panic randomly anytime in the future (once
> issue is encountered) if "/proc/sys/kernel/unknown_nmi_panic" is enabled.
> 
> Thank you very much!
> 
> Dongli Zhang
> 
> On 12/19/22 06:45, Dongli Zhang wrote:
>> Can I get feedback for this patchset, especially the [PATCH v2 2/2]?
>>
>> About the [PATCH v2 2/2], currently the issue impacts the usage of PMUs on AMD
>> VM, especially the below case:
>>
>> 1. Enable panic on nmi.
>> 2. Use perf to monitor the performance of VM. Although without a test, I think
>> the nmi watchdog has the same effect.
>> 3. A sudden system reset, or a kernel panic (kdump/kexec).
>> 4. After reboot, there will be random unknown NMI.
>> 5. Unfortunately, the "panic on nmi" may panic the VM randomly at any time.
>>
>> Thank you very much!
>>
>> Dongli Zhang
>>
>> On 12/1/22 16:22, Dongli Zhang wrote:
>>> This patchset is to fix two svm pmu virtualization bugs, x86 only.
>>>
>>> version 1:
>>> https://lore.kernel.org/all/20221119122901.2469-1-dongli.zhang@oracle.com/
>>>
>>> 1. The 1st bug is that "-cpu,-pmu" cannot disable svm pmu virtualization.
>>>
>>> To use "-cpu EPYC" or "-cpu host,-pmu" cannot disable the pmu
>>> virtualization. There is still below at the VM linux side ...
>>>
>>> [    0.510611] Performance Events: Fam17h+ core perfctr, AMD PMU driver.
>>>
>>> ... although we expect something like below.
>>>
>>> [    0.596381] Performance Events: PMU not available due to virtualization, using software events only.
>>> [    0.600972] NMI watchdog: Perf NMI watchdog permanently disabled
>>>
>>> The 1st patch has introduced a new x86 only accel/kvm property
>>> "pmu-cap-disabled=true" to disable the pmu virtualization via
>>> KVM_PMU_CAP_DISABLE.
>>>
>>> I considered 'KVM_X86_SET_MSR_FILTER' initially before patchset v1.
>>> Since both KVM_X86_SET_MSR_FILTER and KVM_PMU_CAP_DISABLE are VM ioctl. I
>>> finally used the latter because it is easier to use.
>>>
>>>
>>> 2. The 2nd bug is that un-reclaimed perf events (after QEMU system_reset)
>>> at the KVM side may inject random unwanted/unknown NMIs to the VM.
>>>
>>> The svm pmu registers are not reset during QEMU system_reset.
>>>
>>> (1). The VM resets (e.g., via QEMU system_reset or VM kdump/kexec) while it
>>> is running "perf top". The pmu registers are not disabled gracefully.
>>>
>>> (2). Although the x86_cpu_reset() resets many registers to zero, the
>>> kvm_put_msrs() does not puts AMD pmu registers to KVM side. As a result,
>>> some pmu events are still enabled at the KVM side.
>>>
>>> (3). The KVM pmc_speculative_in_use() always returns true so that the events
>>> will not be reclaimed. The kvm_pmc->perf_event is still active.
>>>
>>> (4). After the reboot, the VM kernel reports below error:
>>>
>>> [    0.092011] Performance Events: Fam17h+ core perfctr, Broken BIOS detected, complain to your hardware vendor.
>>> [    0.092023] [Firmware Bug]: the BIOS has corrupted hw-PMU resources (MSR c0010200 is 530076)
>>>
>>> (5). In a worse case, the active kvm_pmc->perf_event is still able to
>>> inject unknown NMIs randomly to the VM kernel.
>>>
>>> [...] Uhhuh. NMI received for unknown reason 30 on CPU 0.
>>>
>>> The 2nd patch is to fix the issue by resetting AMD pmu registers as well as
>>> Intel registers.
>>>
>>>
>>> This patchset does not cover PerfMonV2, until the below patchset is merged
>>> into the KVM side.
>>>
>>> [PATCH v3 0/8] KVM: x86: Add AMD Guest PerfMonV2 PMU support
>>> https://lore.kernel.org/all/20221111102645.82001-1-likexu@tencent.com/
>>>
>>>
>>> Dongli Zhang (2):
>>>        target/i386/kvm: introduce 'pmu-cap-disabled' to set KVM_PMU_CAP_DISABLE
>>>        target/i386/kvm: get and put AMD pmu registers
>>>
>>>   accel/kvm/kvm-all.c      |   1 +
>>>   include/sysemu/kvm_int.h |   1 +
>>>   qemu-options.hx          |   7 +++
>>>   target/i386/cpu.h        |   5 ++
>>>   target/i386/kvm/kvm.c    | 129 +++++++++++++++++++++++++++++++++++++++++-
>>>   5 files changed, 141 insertions(+), 2 deletions(-)
>>>
>>> Thank you very much!
>>>
>>> Dongli Zhang
>>>
>>>
> 
>