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

Joerg Roedel
2020-06-23T11:43:30Z

On Tue, Jun 23, 2020 at 01:14:43PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 23, 2020 at 01:11:07PM +0200, Joerg Roedel wrote:

> > The v3 patchset implements an unconditional shift of the #VC IST entry
> > in the NMI handler, before it can trigger a #VC exception.
>
> Going by that other thread -- where you said that any memory access can
> trigger a #VC, there just isn't such a guarantee.

As I wrote in the other mail, this can only happen when SNP gets enabled
(which is follow-on work to this) and is handled by a stack recursion
check in the #VC handler.

The reason I mentioned the #VC-anywhere case is to make it more clear
why #VC needs an IST handler.

Regards,

Joerg