On Tue, Jun 23, 2020 at 01:43:24PM +0200, Joerg Roedel wrote:

On Tue, Jun 23, 2020 at 01:14:43PM +0200, Peter Zijlstra wrote:

quoted

On Tue, Jun 23, 2020 at 01:11:07PM +0200, Joerg Roedel wrote:

quoted

quoted

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.

If SNP is the sole reason #VC needs to be IST, then I'd strongly urge
you to only make it IST if/when you try and make SNP happen, not before.