> On Jun 17, 2020, at 3:52 PM, Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
>
>> On Jun 17, 2020, at 3:46 PM, John Andersen <john.s.andersen@xxxxxxxxx> wrote:
>>
>> Paravirutalized control register pinning adds MSRs guests can use to
>> discover which bits in CR0/4 they may pin, and MSRs for activating
>> pinning for any of those bits.
>
> [ sni[
>
>> +static void vmx_cr_pin_test_guest(void)
>> +{
>> + unsigned long i, cr0, cr4;
>> +
>> + /* Step 1. Skip feature detection to skip handling VMX_CPUID */
>> + /* nop */
>
> I do not quite get this comment. Why do you skip checking whether the
> feature is enabled? What happens if KVM/bare-metal/other-hypervisor that
> runs this test does not support this feature?
My bad, I was confused between the nested checks and the non-nested ones.
Nevertheless, can we avoid situations in which
rdmsr(MSR_KVM_CR0_PIN_ALLOWED) causes #GP when the feature is not
implemented? Is there some protocol for detection that this feature is
supported by the hypervisor, or do we need something like rdmsr_safe()?
