Re: [PATCH for-4.14] x86/msr: Disallow access to Processor Trace MSRs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.06.2020 14:10, Michał Leszczyński wrote:
> ----- 19 cze 2020 o 13:58, Andrew Cooper andrew.cooper3@xxxxxxxxxx napisał(a):
> 
>> We do not expose the feature to guests, so should disallow access to the
>> respective MSRs.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Wei Liu <wl@xxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> CC: Paul Durrant <paul@xxxxxxx>
>> CC: Michał Leszczyński <michal.leszczynski@xxxxxxx>
>>
>> Paul: For 4.14.  This needs backporting to older trees as well.
>>
>> Michał: CC'ing, just to keep you in the loop.  Xen has some dubious default
>> MSR semantics which we're still in the middle of untangling in a backwards
>> compatible way.  Patches like this will eventually not be necessary, but they
>> are for now.
> 
> 
> As for external IPT monitoring, it would be best if the VM would think
> that IPT is simply not supported at all by the underlying hypervisor.

This is already the case, isn't it? Yet not reporting a feature may
not keep a guest from trying to access the respective MSRs.

Jan