On 2020/6/19 17:40, Vitaly Kuznetsov wrote:
> Guest crashes are observed on a Cascade Lake system when 'perf top' is
> launched on the host, e.g.
Interesting, is it specific to Cascade Lake?
Would you mind sharing the output of
"cpuid -r -l 1 -1" and "cat /proc/cpuinfo| grep microcode | uniq" with us ?
Thanks,
Like Xu
>
> BUG: unable to handle kernel paging request at fffffe0000073038
> PGD 7ffa7067 P4D 7ffa7067 PUD 7ffa6067 PMD 7ffa5067 PTE ffffffffff120
> Oops: 0000 [#1] SMP PTI
> CPU: 1 PID: 1 Comm: systemd Not tainted 4.18.0+ #380
> ...
> Call Trace:
> serial8250_console_write+0xfe/0x1f0
> call_console_drivers.constprop.0+0x9d/0x120
> console_unlock+0x1ea/0x460
>
> Call traces are different but the crash is imminent. The problem was
> blindly bisected to the commit 041bc42ce2d0 ("KVM: VMX: Micro-optimize
> vmexit time when not exposing PMU"). It was also confirmed that the
> issue goes away if PMU is exposed to the guest.
>
> With some instrumentation of the guest we can see what is being switched
> (when we do atomic_switch_perf_msrs()):
>
> vmx_vcpu_run: switching 2 msrs
> vmx_vcpu_run: switching MSR38f guest: 70000000d host: 70000000f
> vmx_vcpu_run: switching MSR3f1 guest: 0 host: 2
>
> The current guess is that PEBS (MSR_IA32_PEBS_ENABLE, 0x3f1) is to blame.
> Regardless of whether PMU is exposed to the guest or not, PEBS needs to
> be disabled upon switch.
>
> This reverts commit 041bc42ce2d0efac3b85bbb81dea8c74b81f4ef9.
>
> Reported-by: Maxime Coquelin <[email protected]>
> Signed-off-by: Vitaly Kuznetsov <[email protected]>
> ---
> - Perf/KVM interractions are a mystery to me, thus RFC.
> ---
> arch/x86/kvm/vmx/vmx.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 36c771728c8c..b1a23ad986ff 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6728,8 +6728,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
>
> pt_guest_enter(vmx);
>
> - if (vcpu_to_pmu(vcpu)->version)
> - atomic_switch_perf_msrs(vmx);
> + atomic_switch_perf_msrs(vmx);
> atomic_switch_umwait_control_msr(vmx);
>
> if (enable_preemption_timer)
"Xu, Like" <[email protected]> writes:
> On 2020/6/19 17:40, Vitaly Kuznetsov wrote:
>> Guest crashes are observed on a Cascade Lake system when 'perf top' is
>> launched on the host, e.g.
> Interesting, is it specific to Cascade Lake?
>
Actually no, just reproduced this on a Haswell system. If you run the
guest with "-cpu host,-pmu" and do 'perf top' (on the host) the guest
crashes immediately.
> Would you mind sharing the output of
> "cpuid -r -l 1 -1" and "cat /proc/cpuinfo| grep microcode | uniq" with us ?
Sure (this is probably unrelated because the issue also reproduces on
Haswell but still):
# cpuid -r -l 1 -1
CPU:
0x00000001 0x00: eax=0x00050657 ebx=0x03200800 ecx=0x7ffefbff edx=0xbfebfbff
# cat /proc/cpuinfo| grep microcode | uniq
microcode : 0x500002c
This is "Intel(R) Xeon(R) Gold 5218 CPU @ 2.30GHz"
--
Vitaly