On Sat, May 23, 2020 at 09:59:24AM +0200, Borislav Petkov wrote: > On Tue, Apr 28, 2020 at 05:16:57PM +0200, Joerg Roedel wrote: > > + /* > > + * Mark the per-cpu GHCBs as in-use to detect nested #VC exceptions. > > + * There is no need for it to be atomic, because nothing is written to > > + * the GHCB between the read and the write of ghcb_active. So it is safe > > + * to use it when a nested #VC exception happens before the write. > > + */ > > Looks liks that is that text... support for nested #VC exceptions. > I'm sure this has come up already but why do we even want to support > nested #VCs? IOW, can we do without them first or are they absolutely > necessary? > > I'm guessing VC exceptions inside the VC handler but what are the > sensible use cases? The most important use-case is #VC->NMI->#VC. When an NMI hits while the #VC handler uses the GHCB and the NMI handler causes another #VC, then the contents of the GHCB needs to be backed up, so that it doesn't destroy the GHCB contents of the first #VC handling path. Regards, Joerg
