On 01.09.2010, at 09:34, Avi Kivity wrote:
> The returned value is completely bogus, and sets reserved bits.
> Return zero instead.
>
> Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 5 +----
> 1 files changed, 1 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1cbf168..a2c03f1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1641,10 +1641,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata)
> data = vcpu->arch.ia32_misc_enable_msr;
> break;
> case MSR_IA32_PERF_STATUS:
> - /* TSC increment by tick */
> - data = 1000ULL;
> - /* CPU multiplier */
> - data |= (((uint64_t)4ULL) << 40);
> + data = 0;
> break;
> case MSR_EFER:
> data = vcpu->arch.efer;
This is the respective code snippet from xnu:
/*
* Get the TSC increment. The TSC is incremented by this
* on every bus tick. Calculate the TSC conversion factors
* to and from nano-seconds.
*/
if (cpuid_info()->cpuid_family == CPU_FAMILY_PENTIUM_M) {
uint64_t prfsts;
prfsts = rdmsr64(IA32_PERF_STS);
tscGranularity = (uint32_t)bitfield(prfsts, 44, 40);
N_by_2_bus_ratio = prfsts & bit(46);
} else {
panic("rtclock_init: unknown CPU family: 0x%X\n",
cpuid_info()->cpuid_family);
}
if (N_by_2_bus_ratio)
tscFCvtt2n = busFCvtt2n * 2 / (uint64_t)tscGranularity;
else
tscFCvtt2n = busFCvtt2n / (uint64_t)tscGranularity;
tscFreq = ((1 * Giga) << 32) / tscFCvtt2n;
tscFCvtn2t = 0xFFFFFFFFFFFFFFFFULL / tscFCvtt2n;
So by passing in 0 here, you effectively make that code divide something by 0 which results in a panic.
Alex
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