Re: Should hvm_hw_cpu's sysenter_eip always be zero after xc_domain_hvm_getcontext_partial()?

[Razvan Cojocaru <rcojocaru@bitdefender.com>]

Thanks for the quick reply!

On 07/31/2015 06:13 PM, Andrew Cooper wrote:
>> Looking in the code, the only two __vmwrite(GUEST_SYSENTER_EIP, ...)
>> calls occur in xen/arch/x86/hvm/vmx/vmx.c. One is in
>> vmx_msr_write_intercept(), but adding a printk() just after produces no
>> output after starting and stopping a guest.
> 
> Write interception for that MSR is disabled (if the hardware supports
> disabling interception) because it is not interesting.
> 
> You can re-enable interception by commenting out the appropriate
> vmx_disable_intercept_for_msr() line in construct_vmcs()

It shouldn't be disabled, it's in the
vmx_introspection_force_enabled_msrs[] list and I'm testing it with
memory introspection.

>> The other is in vmx_vmcs_restore(), which seems to dutifully restore the
>> never-set value of zero after a save.
>>
>> So this doesn't seem to be actually initialized anywhere. Could somebody
>> please recommend the best place to initialize it, and the best value to
>> initialize it with? Or maybe you could point out what I'm missing, if
>> that's the case?
> 
> Are you certain that the guest is actually setting it?  If the guest
> never sets it in the first place, 0 will be the expected value.

That might be it, I'll need to look closer.


Thanks,
Razvan