Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace)

Peter Zijlstra
2020-06-23T12:47:53Z

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.