On Tue, Jun 23, 2020 at 12:51:03PM +0100, Andrew Cooper wrote:

There are cases which are definitely non-recoverable.

For both ES and SNP, a malicious hypervisor can mess with the guest
physmap to make the the NMI, #VC and #DF stacks all alias.

For ES, this had better result in the #DF handler deciding that crashing
is the way out, whereas for SNP, this had better escalate to Shutdown.

Crashing out hard if the hypervisor is misbehaving is acceptable.

Then I'm thinking the only sensible option is to crash hard for any SNP
#VC from kernel mode.

Sadly that doesn't help with #VC needing to be IST :-( IST is such a
frigging nightmare.