Re: [PATCH] KVM: x86: Add three MSRs to the list of ignored MSRs

["Radim Krčmář" <rkrcmar@redhat.com>]

2016-04-14 16:42+0200, Paolo Bonzini:
> On 14/04/2016 15:33, Radim Krčmář wrote:
>> The main bug in KVM is that it allows the guest to think that it runs on
>> CPU that isn't emulated:  any CPU that has MSR_PLATFORM_INFO shouldn't
>> be exposed in KVM.
> 
> That's all of them.  f/m/s values and the model name are a useful
> debugging tool.  Considering that MSR_PLATFORM_INFO is hardly ever used,
> it doesn't seem to be a great compromise.

I don't see that as a compromise.  igd would fail even if we fixed the
host side, so we'll have problems regardless of what we do.

We have a bug, because certain v/f/m/s implies some features (MSRs,
constant_tsc, ...) and those aren't emulated.

I do agree that we don't want to fix the bug, either by whitelisting and
emulating features that makes little sense in virt or by forcing guests
to adopt new v/f/m/s (the latter option is more reasonable), because
rare occurences of the bug take *much* less work to fix on the guest
side.  (The only part I'm concerned about is that we don't have a good
excuse for some guest errors ...)