From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP
 from userspace)
Date: Tue, 23 Jun 2020 14:47:12 +0200
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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.