Re: [PATCH v4 00/75] x86: SEV-ES Guest Support

[Peter Zijlstra]

On Wed, Jul 15, 2020 at 11:34:26AM +0200, Joerg Roedel wrote:
> On Wed, Jul 15, 2020 at 11:24:56AM +0200, Peter Zijlstra wrote:
> > Can we get some more words -- preferably in actual code comments, on
> > when exactly #VC happens?
> 
> Sure, will add this as a comment before the actual runtime VC handler.

Thanks!

> > Because the only thing I remember is that #VC could happen on any memop,
> > but I also have vague memories of that being a later extention.
> 
> Currently it is only raised when something happens that the hypervisor
> intercepts, for example on a couple of instructions like CPUID,
> RD/WRMSR, ..., or on MMIO/IOIO accesses.
> 
> With Secure Nested Paging (SNP), which needs additional enablement, a #VC can
> happen on any memory access. I wrote the IST handling entry code for #VC
> with that in mind, but do not actually enable it. This is the reason why
> the #VC handler just panics the system when it ends up on the fall-back
> (VC2) stack, with SNP enabled it needs to handle the SNP exit-codes in
> that path.

And recursive #VC was instant death, right? Because there's no way to
avoid IST stack corruption in that case.