Re: [PATCH v6 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active

[Sean Christopherson]

On Mon, 2018-09-10 at 17:53 +0200, Borislav Petkov wrote:
> On Mon, Sep 10, 2018 at 08:15:38AM -0500, Brijesh Singh wrote:
> > 
> > > 
> > > Now, the real question from all this SNAFU is, why can't all those point
> > > to a single struct pvclock_vsyscall_time_info and all CPUs read a single
> > > thing? Why do they have to be per-CPU and thus waste so much memory?
> You forgot to answer to the real question - why do we need those things
> to be perCPU and why can't we use a single instance to share with *all*
> CPUs?

I can't speak to the actual TSC stuff, but...

The pvclock ABI includes a per-vCPU bit, PVCLOCK_GUEST_STOPPED, to indicate
that the VM has been paused by the host. ÂThe guest uses this information to
update its watchdogs to avoid false positives. ÂI have no idea if there are
use cases for setting STOPPED on a subset of vCPUs, but the ABI allows it so
here we are...