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

[Joerg Roedel]

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.

> 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.

Regards,

	Joerg