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

[Dongli Zhang]

This is to rebase the patchset on top of the most recet QEMU.

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. It has been queued to kvm-x86 next by Sean.

[PATCH v7 00/12] KVM: x86: Add AMD Guest PerfMonV2 PMU support
https://lore.kernel.org/all/168609790857.1417369.13152633386083458084.b4-ty@google.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