Using _safe has it's own issues if noone checks the errors. On March 22, 2014 5:27:59 AM PDT, Gleb Natapov <gleb@xxxxxxxxxx> wrote: >On Sat, Mar 22, 2014 at 11:05:03AM +0100, Peter Wu wrote: >> On Saturday 22 March 2014 10:50:45 Gleb Natapov wrote: >> > On Fri, Mar 21, 2014 at 12:04:32PM -0700, Venkatesh Srinivas wrote: >> > > On Fri, Mar 21, 2014 at 10:46 AM, Peter Wu <peter@xxxxxxxxxxxxx> >wrote: >> > [skip] >> > >> > > When -cpu host is used, qemu/kvm passed the host CPUID F/M/S to >the >> > > guest. intel_pmu_cpu_*() -> intel_pmu_lbr_reset() uses rdmsr() / >> > > wrmsr(), rather than the safe variants; if KVM does not support >the >> > > particular MSRs in question, you will see a #GP(0) there. See >> > > https://lkml.org/lkml/2014/3/13/453 for a similar bug other PMU >code. >> > > >> > When kernel is compiled with guest support all rdmsr()/wrmsr() >become _safe(), >> > so the question for Peter is if his guest kernel has guest support >enabled? >> >> Linux guest support (CONFIG_HYPERVISOR_GUEST) was not enabled, see >> .config in the first mail[1]. Enabling that option does not change >the >> situation. >> >> With CONFIG_PARAVIRT and CONFIG_KVM_GUEST enabled, the PMU GPF is >gone, >Yeah, it should be PARAVIRT indeed since rdmsr()/wrmsr() is substituted >by _safe() >using paravirt calls. > >> but now I have a NULL dereference (in rapl_pmu_init). Previously, >when >> `-cpu SandyBridge` was passed to qemu, it would show this: >> >> [ 0.016995] Performance Events: unsupported p6 CPU model 42 no >PMU driver, software events only. >> >> The same NULL pointer deref would be visible (slightly different >> addresses, but the Code lines are equal). With `-host`, the NULL >deref >> with `-cpu host` contains: >> >> [ 0.016445] Performance Events: 16-deep LBR, IvyBridge events, >Intel PMU driver. >> >> Full dmesg below. >> >I am confused. Do you see crash now with -cpu SandyBridge and -cpu >host, or -cpu host only? > >-- > Gleb. -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
